30 August 2015

The Boeing YB-40 Bomber Escort and Its Tall Tales

Boeing YB-40 in flight. Note the second dorsal turret.
It quickly became apparent with the start of daylight strategic bomber missions over Europe that fighter escort was desperately needed to get the heavy bombers to their targets and back. During the design phase of the Boeing B-17 Flying Fortress, air doctrine of the day called for the mutually supporting defensive fire from the bomber formation to be sufficient defense against enemy fighters. Early B-17 missions were against targets in northern France which were well within the range of Royal Air Force Spitfires which could provide escort cover- but as the Eighth Air Force began to dispatch its growing B-17 force against further targets, the Spitfires lacked the range. The Republic P-47 Thunderbolt and North American P-51 Mustang had yet to reach sufficient numbers in Europe to provide long-range escort and the only fighter in theater with the range, the P-38 Lightning, was desperately needed in the North Africa campaign. In those early days of unescorted daylight missions, only a quarter of combat losses were coming from anti-aircraft flak- the majority of bomber losses came from Luftwaffe fighters. The only aircraft with the range to escort the B-17s was quite obviously (at least to planners then) another B-17, so why not swap out a bomb-load for increased defensive armament as a large bomber escort? The passage of time has us not knowing who came up with the idea of a heavily armed B-17 as an escort, but in November 1942 the first XB-40 was ordered- taking a stock B-17F Flying Fortress from the license production line at Lockheed Vega (both Lockheed and Douglas were building Flying Fortresses to augment Boeing's own production), the XB-40 was modified with a chin turret with twin fifty-caliber guns to defeat head-on attacks by Luftwaffe fighters. In addition, the waist positions were staggered so the waist gunners had more freedom of movement and each gunner got a twin fifty-caliber on a flexible mount instead of a single fifty-caliber gun which was standard. Finally, a second dorsal turret was added where the radio room was located, this turret also had twin fifty-caliber machine guns. Space in the bomb bay was devoted to additional ammunition storage and fuel. Compared to a standard B-17F, the XB-40 had three times the ammunition for its beefed up gun armament. 

Interior layout of the YB-40 showing the increased guns.
A further twenty-four B-17Fs were taken from Lockheed Vega's production and delivered to the Douglas B-17 plant in Tulsa for modification to YB-40 standard (the "Y" prefix indicating a service test aircraft as opposed to an experimental prototype which would use the "X" prefix). There were only minor differences between the first XB-40 and the YB-40 series of aircraft. Some sources suggest different armament combinations were trailed including cannons, but the aircraft were sent to Europe standardized on the Browning fifty-caliber machine gun for all the defensive positions. The 92nd Bomb Group at RAF Alconbury would be the first unit to take the YB-40 into combat to prove the concept. Of that group of twenty five aircraft (including the XB-40), thirteen would be sent to Europe- one was lost on the ferry flight, making a forced landing in a Scottish bog, leaving twelve to continue on to Alconbury. The first mission was flown on 29 May 1943 with seven YB-40s accompanying a B-17 force to hit the Kriegsmarine U-boat pens at Saint-Nazaire, France. The YB-40s, loaded with extra guns and ammunition, were slower than regular B-17Fs and handling at altitude was sluggish. The entire formation had to slow down to allow the YB-40s to keep up. On the return leg, the now empty B-17Fs could fly higher and faster no longer burdened with their bomb-loads, but the YB-40s still had their guns as they didn't exactly lighten over the course of the mission as they didn't have a heavy bomb-load to drop. Marauding German fighters focused on stragglers in the bomber formations and while the YB-40s had the defensive fire to fend off the attacks,  no one was thrilled about the prospect of being the formation straggler on every mission. The Eighth Air Force command was less than impressed- the last mission was flown on 29 July 1943 with only two months of operating experience- nine missions were flown with the loss of one aircraft. Five German fighters were confirmed as shot down by the YB-40s with two probable kills. It was hardly a resounding performance and the YB-40 program quietly wound down. Through 1943 until early 1944, the YB-40s returned to the United States. Twelve aircraft of the original twenty four never left the United States and were ultimately scrapped. 

Layout of the YB-40's additional gun armament.
The experience of the YB-40, though, did leave a legacy with the B-17 force. The next variant of the B-17 to follow the B-17F, the B-17G, featured the chin turret and the staggered waist gun positions that were used on the YB-40s. Some sources indicate that the improved "Cheyenne tail turret" (so named from the United Air Lines modification center in Cheyenne, Wyoming) was also an outgrowth of the YB-40 program. 

Two tall tales have sprung up from the YB-40 story that are often repeated on websites, publications and even books. Both of them are just that- fanciful stories and we'll discuss both of them for the record and why they're tall tales and not true historical events. 

The first story concerns a B-17 pilot with the Twelfth Air Force in the Mediterranean named Harold Fischer (in some stories spelled Fisher). Returning to their base in North Africa after a mission against the Italian island of Pantellaria, Fischer's B-17 lagged behind the formation as it had two of its engines shot out. A lone P-38 Lightning formed up on his bomber and offered to escort them. It soon took up position behind the crippled B-17 and shot it down over the sea with Fischer as the only survivor. His story was met with disbelief until USAAF intelligence officers corroborated his story that a P-38 that had gotten lost had fallen into the hands of the Italians and it was being flown by a Regia Aeronautica ace, Guido Rossi, to shoot down B-17 stragglers. Fischer was the first B-17 crewman to have survived Rossi's ruse as he had already downed nine bombers with the captured P-38. Fischer came up with a plan to exact revenge on Guido Rossi and a YB-40 was requested from the Eighth Air Force in August 1943 which Fischer would fly, playing the part of a B-17 straggler to trap Rossi. After two weeks of flying, they hadn't gotten Rossi but the Italian added more kills to his P-38. Determined to get him, Fischer worked with Allied intelligence to find out as much as he could about Guido Rossi and learned his wife and child were living in an Italian city that was in Allied hands. Fischer went to the home of Gina Rossi to meet her and had an artist paint a portrait of her on the side of the YB-40 which he aptly named "Gina". 

On the next mission to Pisa, Italy, Fischer's YB-40 took heavy damage and ended up getting met by Rossi's P-38. Noting the nose art, Rossi asked Fischer if the woman on the nose of the plane was from his own town. Realizing they had Rossi, Fischer confirmed Rossi's suspicions and began to sing the praises of Gina's lovemaking abilities. Filled with rage, Rossi attacked the YB-40 and a running gun duel ensued with Rossi at one point trying to ram the bomber. Rossi was eventually shot down over the sea and survived. As the story goes, Fischer got the Distinguished Flying Cross for it and the two flyers eventually met after the war, but Fischer was killed in a crash during the Berlin Airlift.

Sounds like a great story, but there was no Italian ace named Guido Rossi. A P-38 did fall into Italian hands during the war and its pilot was known and the aircraft as only flown in an evaluation role. There is no record of the YB-40 operating in the Mediterranean theater of operations- while there were two bomb groups with B-17s assigned to the Twelfth Air Force, neither of them operated the YB-40 either. And most damning to the veracity of this story, there is a pilot named Harold Fischer who got the DFC- but he was USAF F-86 Sabre pilot in the Korean War- he was the 25th ace of the war and was imprisoned by the Chinese after getting shot down and wasn't released until 1955. 

The second tale relates to one 1st Lt. Harry Reid with the 95th Bomb Group of the Eighth Air Force who with one of his lead pilots, had noted a lone B-17 that would tail their bomber formations on their missions over Europe. In June 1944 as the story goes, Reid and his lead pilot, Captain Glenn Infield, hatched a plan on their own initiative to use a parked YB-40 at their base to get this lone B-17 which they suspected was a captured Flying Fortress being flown by the Luftwaffe to tail formations and give position, altitude and heading information on the formations to defending Luftwaffe fighters. On a mission against a target in Brussels, Reid and Infield set their plan in motion. Sighting the lone B-17, they closed on it. The aircraft then veered away from them, confirming their suspicions as a one B-17 would have formed up with any other B-17 right away for mutual defensive fire from the gunners. Pursuing the German-flown Flying Fortress, the YB-40 was bounced by six Focke Wulf Fw 190 fighters. Reid and Infield astutely realized if they stayed close to the captured B-17, it made the Fw 190's task harder out of fear of hitting the wrong B-17. Their radio operator happened to speak fluent German and he got on the Luftwaffe's fighter frequency and directed the Fw 190 pilots to attack the captured B-17 while they made a sharp break to the right. Thinking they had gotten direction from their own B-17, the Fw 190 pilots made their attack before their own B-17 could protest! With the captured B-17 damaged, the YB-40 completed a full turn to the right and came up and behind the other Flying Fortress, finishing it off just as escort fighters arrived on the scene. Because their plan was hatched of their own initiative without the approval of their superiors, Reid and Infield were never formally decorated for their actions. 

Again, sounds like a great story, but the last YB-40s were documented to have returned to the United States by March 1944. Most of the original twelve that flew missions had returned through 1943 but three were left in Great Britain at the start of 1944. One returned to the United States in January 1944 and the last two returned in March 1944, making the timeline of this second tale impossible. In addition, while the 95th Bomb Group was co-located with the 92nd Bomb Group at RAF Alconbury, there is no documentation of the 95th BG having flown the YB-40. Only the 91st, 92nd, and 303d BGs ever flew the YB-40. 

Sources: Aerial Gunners: The Unknown Aces of World War II by Charles Watry and Duane Hall. California Aero Press, 1986, p167-174. "Brilliant Mistakes: The YB-40" by Robert Dorr. Defense Media Network at http://www.defensemedianetwork.com/stories/my-brilliant-mistake-the-yb-40/. Photos: USAF Museum, 92nd Air Refueling Wing Historians, Squadron Publications via War Thunder Forums.

25 August 2015

The Jendrassik CS-1: The World's First Turboprop Engine

Schematic of the CS-1 engine
"Cs-1 engraving" by User:Kaboldy - Hungarian wikipedia. 
In 1937 Hungarian engineer Gyrogy Jendrassik had done a test run of a 100-horsepower gas turbine and the knowledge he gained from developing that small turbine he used to develop a larger turbine that would become the CS-1, the world's first working turboprop engine. Conducting his research at the Ganz Wagon and Engine Works in Budapest, Jendrassik's turboprop prototype was completely indigenous in design with many features seen in turbine engines today like an annular flow reverse combustor, extended-root turbine blades to reduce heat flow to the turbine discs, turbines mounted on bearings and air-cooling of the turbine discs. Making its first test run on the bench in August 1940, the CS-1 had an annular intake that surrounded a front-mounted reduction gearbox, a 15-stage axial compressor, and 11-stage axial turbine behind the combustion chamber and an annular exhaust duct.  Keep in mind at this time that most jet engines under development were centrifugal in layout, axial designs being more advanced that the state of the art of the day with only the Junkers Jumo 004 engine (the power plant of the Messerschmitt Me 262) being the only axial flow engine to reach production during the war. The layout of the CS-1 was remarkably advanced for its time and Jendrassik anticipated that the CS-1 would produce 1,000 horsepower for a lower engine weight than a 1,000 horsepower piston engine. Having done preliminary bench testing for the engine, Jendrassik sought an airframe application for his turboprop engine to expand the testing envelope. 

Hungarian engineer Laszlo Varga of the Technical Institute of Aviation set out to create a fighter-bomber at Jendrassik's request that would use two CS-1 turboprop engines. The design had been alternately designated RMI-1 (for the name of Varga's institute in Hungarian) or X/H. The aircraft was a low wing design with underslung nacelles for the turboprop engines and had two to three crew members depending on the mission to be undertaken. With two CS-1 engines, it was anticipated that the X/H would have a maximum level speed of 335 mph.

Profile art of the Varga X/H fighter-bomber
Model box art via the International Resin Modelers Association
Construction problems beset the X/H prototype leaving it unable to handle the stresses and anticipated power output of the twin turboprops. Also affecting the program were issues with the test runs of the CS-1 engines that could only achieve 400 horsepower. With the signing of a mutual defense pact between Hungary and Germany in June 1941 it was decided to license produce the Daimler-Benz DB 605 piston engine and purchase the Messerschmitt Me 210 to meet the specifications planned for the Varga X/H. Work continued on the X/H, though, and the prototype was completed in 1942 and it was modified to take DB 605 engines to allow a limited flight test program to take place. Taxiing trials and high speed runs were undertaken, but the X/H prototype was destroyed in a USAAF bomber attack in June 1944 before it could make its first flight.

For his work on the CS-1 turboprop engine, Gyorgy Jendrassik was elected to the Hungarian Academy of Sciences in 1943, however, his anti-Communist sentiments rendered him untrustworthy by the postwar Soviet-dominated regime. He left for Argentina and worked for General Juan Peron for a time before returning to Europe and settling in Great Britain, working as an engineering consultant for Power Jets, the company set up by British jet engine pioneer Frank Whittle. Laszlo Varga's fate is unknown following the fall of Hungary to the Communist regime. 

Source: Air Enthusiast, Volume One, William Green, managing editor, Gordon Swanborough, editor. Pilot Press Ltd, 1971, p53. Photos: Wikipedia, International Resin Modelers Association.

20 August 2015

Birth of the Airbus Family: The A310

The Airbus A310 prototype takes flight on 3 April 1982.
In the days following the start of the 1973 Yom Kippur War in Middle East in October that year, the oil producing nations of the Middle East responded to American materiel support of Israel with an oil embargo that sparked a worldwide economic crisis as the price of oil abruptly shot upwards from $3/barrel to over $12/barrel in a short period of time. As a result, the airline industry worldwide embraced fuel efficiency as the new driver for future aircraft designs. While there were high-bypass ratio turbofans that powered the new widebody designs that were entering service (Boeing 747, Douglas DC-10, and Lockheed L-1011 Tristar), turbojets and low-bypass ratio turbofans were still commonplace in the short to medium-haul fleets worldwide. Many airlines indicated to the major manufacturers that there was a market need for a fuel-efficient aircraft in the 150-200 seat range over short to medium haul ranges. Of the big three manufacturers in the United States who dominated the world commercial airliner market, Boeing's plans were the most ambitious with the launch of not just one aircraft, but two aircraft with a common cockpit with the Boeing 757 and 767. It was in many ways the biggest gamble Boeing had ever undertaken, bigger than building the Dash 80 demonstrator that led to the 707 and even bigger than the launch of the 747 ten years earlier. News of Boeing's plans put pressure on Airbus Industrie to respond as all it had produced by that point was the A300. While there were a range of A300 variants with varying engines, payload and fuel capacities, they were all still essentially the same aircraft and hardly a family of aircraft. Two of the primary founders of Airbus and their heads, Roger Béteille (technical director) and Henri Ziegler (general manager), strongly believed that Airbus needed to emulate Boeing's strategy of building a whole family of different aircraft for different markets if the whole enterprise was to have a future beyond the A300. Boeing's idea for commonality with the 757 and 767 designs resonated with the Airbus team who was commonality among varied designs as a way of proving value to the airline customers, not to mention it would be a strong incentive for an Airbus customer to stay loyal to Airbus in the future.

Part of the problem Béteille and Ziegler faced was that most of the Airbus consortium partners saw the A300 as the end result of cooperation instead of the starting point for future cooperation. A lot of that was driven by the atmosphere of fiscal austerity of the 1970s in the wake of the 1973 oil crisis- Airbus' partner nations were hesitant of putting up more money into the venture, particularly when Airbus was still a bit player on the world market despite the success of the A300. In 1978, for example, Airbus delivered 15 aircraft, all of them A300s. That same year Boeing delivered 203 aircraft across three product lines- the 727, 737, and 747. In fact, it wouldn't be until 2003 that Airbus would deliver more aircraft in a single year than Boeing. When Boeing launched the 757 and 767 programs, they were also capitalizing on market vulnerabilities experienced by McDonnell Douglas and Lockheed in the wake of their trijet programs- Airbus wasn't really on Boeing's radar screen at the time. Despite the market effects on McDonnell Douglas and Lockheed, they were still delivering aircraft as well which were entering service on top of Boeing's numbers. You can imagine what a tall order it was for Béteille and Ziegler to convince the Airbus consortium partners that there was value and potential for the long haul beyond the A300 at a time when they were only building less than 5% of the world's commercial jetliners. It wasn't until mid-1975 that the board of Airbus Industrie endorsed the plan for a family of aircraft- and that endorsement is a testament to the persuasive powers of Roger Béteille and Henri Ziegler. In his book Close to the Sun: How Airbus Challenged America's Dominance of the Skies, author Stephen Aris calls that 1975 decision as the most critical decision in Airbus' history. If Airbus failed, then it was only one aircraft, the A300, that failed. But if they became successful, then that one aircraft wouldn't be enough. The leadership of Airbus Industrie by that point had proven themselves remarkably adept in getting the A300 into production and to market while balancing the interests of the partner nations in the consortium. 

Winning a Swissair order was a strategic priority for Airbus
With the backing of the consortium to expand the Airbus product line beyond the A300, the next task at hand was to determine the configuration of the new addition. The first iteration dated back to the oil crisis of 1973 when A300 sales were near dormant (only four A300s were delivered in 1974). In response to what was seen as an evolving market for something smaller than the A300, what was designated the B10 was a minimum-change variant of the A300 that had a shorter fuselage but the same wing and empennage as the larger aircraft. However, the B10 proposal created a significant amount of discord at all levels of Airbus as the consortium partners argued whether it was needed or not. Lufthansa in particular was keen for a smaller A300 derivative and this had gotten the support of Swissair. In those days, Swissair was one of those flagship customers every commercial airframe builder wanted as a customer. They were a tough customer known to be one of the most difficult airlines to negotiate with- but a Swissair order was badge of prestige for any commercial aircraft design and with Swissair now allying with Lufthansa on interest for a smaller A300 derivative, winning Swissair as a launch customer soon became one of Airbus' primary strategic goals. 

By the time the two airlines were briefed on the B10 proposal, Boeing was well on its way to launching the 757/767 program and compared to those aircraft, the B10 had no fans with either Lufthansa or Swissair. Their objections of the proposal stemmed from two points- the first one was that by the time of proposed service entry, the B10 design would be based on technology and a design that was at least a decade old and more importantly, it had a worse payload fraction than the A300. The payload fraction is one way of measuring an aircraft's efficiency- how much payload can it carry compared to its weight. Since the B10 design had a shorter fuselage married to the A300's wings, it had less passengers (therefore less revenue) to offset the costs of carrying a heavier wing structure. This is one of the reasons why shrinks of commercial airframes tend to not do well in the market- like the A318, 737-500, or 747SP, for example. If the B10 proposal was ever going to get off the drawing board, it needed a lighter wing and whole host of improvements over the A300 to win over the airlines who were being offered the latest in technology with the 757/767. In an unusual twist of history, the prospect of trans-Atlantic cooperation offered an potential answer to Airbus' dilemma. Why not combine Airbus' growing widebody fuselage expertise with the technology and industrial muscle of the United States? The first feelers on such an idea came from McDonnell Douglas in the spring of 1975 for a joint venture for a 200-seat design called the DC-X-200. McDonnell Douglas had long been considering a twin-engine version of the DC-10 and the DC-X-200 was the latest iteration along those lines. However, once discussions moved beyond engineering to management, the talks quickly collapsed. That summer another offer came from Boeing who thought there would be some synergies with the B10 proposal and the 767 program. Whether Boeing was serious or just trying to distract Airbus is still a source of debate to this day, but the proposal would have consisted of the A300-based fuselage and 767 wings and empennage. At the end of the day, however, Airbus lost interest as it became apparent that they would end up a Boeing subcontractor in the joint venture. 

Lufthansa was an early A300 customer who drove the design of the A310.
Still keen to win over Lufthansa and Swissair, Airbus decided to follow as Boeing had done with the 757/767 and go with a two-crew flight deck and CRT displays. That would prove to be a relatively easy step to take but it still provoked the ire of the pilots' unions of several European carriers. The need for a new wing, however proved to continue to be problematic. I had posted previously that it had taken the personal intervention of a German politician, Franz Josef Strauss, to fund the A300's wing development and construction by Hawker Siddeley as a result of the British government's withdrawal from the Airbus consortium. Hawker was still the center of the most advanced wing design work in Europe and was in the process of merging with several other entities to form British Aerospace (BAe). With British Aerospace being majority owned by the government, there was considerable anguish at Airbus as to whether or not BAe would participate in the B10 project given the British pull out of the Airbus consortium in 1969.  When Hawker elected to remain an Airbus participant despite the pullout, they had absorbed a portion of the costs of wing development. Now that Hawker was part of BAe, no one was sure that the new entity was willing to front such costs again for the B10 project. Airbus decided at that point to turn to its partners for a wing design- Aerospatiale and VFW-Fokker each submitted wing designs and Roger Béteille was sure that whoever was chosen, it would be the end of Airbus as the other partner would feel jilted. As it turned out, neither was chosen- the German design was aerodynamically superior but the French design was structurally superior. A joint-wing design center was established to combine their efforts and word of this got back to BAe quite quickly that their replacement was in the works. 

The exact political machinations in the UK that resulted will be the subject of a future blog article, but they were contentious with pro-Airbus factions in the British government and those who favored a joint-venture with Boeing on the 757. At the end of the day, however, BAe did end up designing and fabricating the wing which was not only lighter, but was of supercritical section which made it not only more aerodynamically efficient but also offset the smaller size with a deeper airfoil section which offered more fuel capacity. Getting the wing also meant that the British eventually rejoined the Airbus consortium with a 20% share. On 9 June 1978, Lufthansa and Swissair issued a joint specification for the new aircraft and within a month announced intentions of placing orders for what was launched as the Airbus A310. On 15 March 1979, Swissair announced its launch order for 10 aircraft and 10 options with plans to use the A310 as a replacement for its legacy DC-9 fleet on its major intra-European routes. Lufthansa quickly followed with an order for 10 aircraft and soon after Air France and Iberia also placed orders, assuring the production and success of the A310. When the A310 prototype flew, it would later wear Swissair's colors on the right side and Lufthansa's colors on the left side. Many of the advances of the A310 were later incorporated into an upgrade of the A300, the A300-600. 

Source: Close to the Sun: How Airbus Challenged America's Domination of the Skies by Stephen Aris. Agate Books, 2002, pp 90-95. Photos: Wikipedia

15 August 2015

The Atomic Neptunes: The Navy's Interim Nuclear Bombers

P2V-3C JATO takeoff from the USS Midway
Not often realized in aviation history is the key role naval personnel played in the development and the deployment of the first atomic bombs that closed out the Second World War. In March 1943, Navy captain William Parsons was assigned to the Manhattan Project's Ordnance Division as he had had prior experience in the development of the proximity fuse for anti-aircraft shells. While he also contributed to the design of the atomic bomb's proximity fuse, he ultimately became responsible for the planning and execution of the US Army Air Force's use of the bombs against Japan. At Titian Island in the Marianas, it was Captain Parsons who was in charge of the bomb assembly and check out. The early bombs of those days had a core that was separate from the main core, this way the two parts were each of subcritical mass and unlikely to detonate as a safety measure. Once airborne, the "weaponeer" was responsible for inserting the core into the atomic bomb to arm it. The weaponeer also acted as the mission's tactical commander as they had the final authority on the bomb's use. On the Enola Gay's mission against Hiroshima, Captain Parsons was aboard as the weaponeer and armed "Little Boy" prior to its use. Parson's director of operations in the Manhattan Project was another naval officer, Commander Frederick Ashworth, a former Grumman TBF pilot. On the second mission against Nagasaki, Commander Ashworth was the weaponeer aboard Bock's Car. Though delivered to their targets by USAAF Boeing B-29 Superfortresses, both atomic bombs were armed by naval officers in flight and in essence, naval officers acted as the mission commanders. Despite the primacy of the Navy's carrier battle groups in the Pacific War, the Navy was well aware of the potential power of nuclear weapons in the postwar period. In September 1945 right after the Japanese surrender, the Chief of Naval Operations (CNO) established the Navy's "Special Weapons Division" which was headed by a vice-admiral. Planning immediately began for a new, much larger aircraft carrier that would carry the Navy's planned nuclear strike force. Until this supercarrier was launched, the three biggest aircraft carriers of the US Navy would be responsible for deploying nuclear weapons- these three ships were the Midway-class carriers- the USS Midway, USS Franklin D. Roosevelt, and the USS Coral Sea. In December 1945, the Navy laid out a three-phase carrier-based strategic bomber plan- Phase 1 called for modest capability bomber to speed its introduction and deployment to the fleet. That aircraft became the North American AJ Savage. Phase 2 was eventually dropped as it was decided to adopt the Allison T40 turboprop engine for an improved version of the AJ Savage- that aircraft was the failed XA2J Super Savage. Phase 3 was for the definitive jet-powered nuclear strike bomber that the Navy really wanted, and that aircraft would eventually become the Douglas A3D Skywarrior. 

North American Aviation received the contract to start work on the AJ Savage in June 1946. With the creation of an independent United States Air Force with the passage of the National Security Act of 1947, the assertive leadership of the USAF moved to become to sole user of nuclear delivery in the US military and pushed to relieve the Navy of its strategic ambitions. A rancorous conference chaired by Secretary of Defense James Forrestal in March 1948 in Key West, Florida, resulted in an agreement that the Navy could not only keep its land-based patrol bomber force but could continue development of its strategic air arm as it was consistent with the aims "to conduct air operations as necessary for the accomplishment of objectives in a naval campaign". Since the Navy's planned nuclear targets were all Soviet naval bases, it was given that the USAF's Strategic Air Command would be responsible for the targeting of Soviet urban and industrial centers while the Navy targeted naval bases and other military installations that threatened operations at sea. This didn't sit well with the USAF, but Forrestal's decision was further cemented at a second meeting held at the Naval War College in Newport, Rhode Island, in August 1948. As an interesting historical note to those meetings, the Navy had its own nuclear war plan independent of the USAF's plans until 1960, when both services' plans were integrated into what was called the Single Integrated Operations Plan, or SIOP. 

North American AJ-1 Savage, the Neptune's replacement.
With the prototype North American XAJ Savage making its first flight in May 1949, it was imperative during the development of the Savage that the Navy establish some sort of nuclear delivery capability from its aircraft carriers as soon as possible. The most ideal candidate aircraft to get some sort of interim capability fielded was the Lockheed P2V Neptune. In 1946, a modified Neptune named "Truculent Turtle" made a record-breaking long distance flight from Australia to Ohio, over 11,000 nautical miles without refueling. With the plans for the Midway-class carriers to operate in the Mediterranean with the nuclear-armed Neptunes, a flight from the eastern Med to Moscow was significantly less than that of the Truculent Turtle's flight and if the targets were coastal naval bases, the range required was even less. With a gross weight well in excess of the catapults of the Midway-class ships, the modified Neptunes would use eight 1,000 lb-thrust JATO rockets with a near-full length deck run of 900 feet and the starboard wingtip clearing the island by only 10 feet. The modified Neptunes were designated P2V-3C and only twelve such aircraft were ordered- since there were only three Midway-class ships and a small number of the Mk 1 bomb (based on the Little Boy design) available, the interim strike force would be very small until the AJ Savage became operational. The more advanced Mk 4 bomb which was based on the Fat Man design used on Nagasaki was too large for the Neptune's bomb bay- but the AJ Savage was designed from the outset to be able to carry the larger Mk 4 bomb. 

At first it was planned to give the P2V-3Cs the ability to return to the carrier after their missions. One of the twelve aircraft modified got a tail hook and around 128 field arrested landings were practiced both at Lockheed's facility at Burbank Airport and at the Navy's flight test center at NAS Patuxent River in Maryland. These flights were flown by another naval aviator who was a veteran of the Manhattan Project, Commander John Hayward. During the war he was assigned to China Lake where he worked on the implosion device used on Fat Man to start the nuclear chain reaction that resulted in detonation. Commander Hayward even flew the P2V-3C on touch and goes off the USS Franklin D. Roosevelt, but no arrested landings at sea were made. It was found that the Neptune's structure wasn't strong enough for carrier landings and the aircraft that Hayward flew on land-based arrested landings had numerous structural deformities as a result. Since there wasn't time to beef up the structure of the Neptune, the P2V-3Cs would have be craned aboard the Midway-class ships dockside and then, after completion of the mission, either ditch alongside the carrier or land at a friendly airfield. This made the P2V-3C aircraft pretty much a single-use weapon. 

Internal layout of the P2V-3C. Note the fuel tanks in the nose and aft fuselage.
Additional fuel tanks were added in the wings and fuselage of the Neptune to create the P2V-3C. Total internal fuel over a standard P2V patrol bomber was increased by an astounding 75%! The P2V-3C carried 4,120 gallons of fuel over the standard P2V's 2,350 gallons. Anything unnecessary to the nuclear delivery mission was deleted, especially if it caused drag- so the dorsal gun turret, nose turret, rocket launcher provisions on the wings and multiple antennas were removed. An AN/APS-31 search and navigation radar replaced the nose turret and it worked with a radar bomb sight. Even the astrodome was removed to reduce drag, sextant shots for navigation would be done via a periscope. Since the mission endurance of the P2V-3C would outlast the oil capacity of the Wright R-3350 radial engines, a 38-gallon oil tank was installed (in fact, the navigator sat on it) with plumbing to keep the engines replenished with oil during the mission. To further save on weight, even the emergency hydraulic system was removed from the P2V-3C. A pair of 20mm tail guns were kept for self defense along with radar detection equipment (but no countermeasures or jamming capability was installed) and the crew was reduced to just four: pilot, copilot/weaponeer, bombardier/navigator, and radioman/tail gunner. 

The first P2V-3C takeoff from a carrier took place in April 1948 fro the USS Coral Sea and a rapid series of demonstrations were made at increasing weights to show that a fully-fueled and loaded Neptune could make it off the carrier with a JATO-assist deck run. On one demonstration flight, Captain Hayward had the second Secretary of Defense, Louis Johnson, in the right seat. It was Johnson who succeeded Forrestal as SecDef and interestingly, just months before his flight on a P2V-3C demonstration takeoff, he had canceled the Navy's first supercarrier, the USS United States. Through 1948, the Navy conducted a series of long range missions from a Midway-class carrier to demonstrate the concept, a simulated weapon delivery and recovery to a friendly air base. Should the Neptune crew elect to ditch along side the carrier, a special flap was added to the underside of the P2V-3C called a "hydroflap" that helped keep the nose of the aircraft from boring into the water during ditching. 

With the deployment of the P2V-3C nearing, the Navy formed three Special Weapons Units- one each for each of the Midway-class aircraft carriers. Based and trained at Kirkland AFB in Albuquerque, New Mexico, where the Department of Energy in cooperation with the USAF had a nuclear technical facility, each unit would be responsible for the assembly, maintenance, and check out of each weapon. The technology of the day meant it took about 50 men and 80 hours to carry out a bomb aseembly and disassembly for maintenance checks. Modifications to each Midway-class carrier provided for facilities for bomb handling, storage, and maintenance with a special Marine Corps detachment for security. The first Navy heavy attack squadron was Composite Squadron 5 (VC-5), established at Moffett Field, California on 9 September 1948. VC-5's commanding officer was Commander Frederick Ashworth, the weaponeer on Bock's Car. In the following January, Captain John Hayward assumed command with Ashworth as his XO. The first P2V-3Cs were delivered to the squadron in November 1948. JATO training at NAS Patuxent River began in February 1949 and by March, three aircraft were craned aboard the USS Coral Sea for its first exercises. By April 1949, all three Midway-class carriers were ready for deployment- all three would be homeported at Norfolk, Virginia, on the East Coast since their deterrent patrols would be in either the Mediterranean or North Seas. 

JATO launch from the USS Franklin D. Roosevelt
It was by this time that the wisdom of using the Neptune as an interim aircraft proved wise- North American was running into development issues with the AJ Savage. Even though the deployment of the P2V-3C coincided with the arrival of the first AJ Savage aircraft, the early AJs were so unreliable and trouble-prone, most training had to be done with the Neptunes. By April 1950, VC-5 was sending detachments to the carriers that had both the AJ Savage and the P2V-3C Neptune. The AJs were used for carrier landing qualifications since the Neptunes lacked return provisions. The first operational deployment took place in January 1951 when VC-5 went aboard the USS Franklin D. Roosevelt. The aircraft weren't on the ship, though- the FDR left Norfolk for the Mediterranean with its complement of bombs and its attendant Special Weapons Unit. Six AJ Savages and three P2V-3C Neptunes departed Norfolk later for Port Lyautey, Morocco, to catch up with the carrier. Continued problems with the AJ kept them shore based. Since the Neptunes couldn't return to the ship, they were also shore-based in Morocco as well and would be craned aboard the carrier had tensions increased. It wasn't a practical arrangement but it was the only arrangement. So as to not alert the Soviets, Neptunes were craned aboard which ever Midway-class carrier was in the Mediterranean and practice launches carried out on a routine basis. Depending on the planned mission range, no more than three to four P2V-3C Neptunes could operate from the carrier- few of the carrier's air wing could be on deck as the Neptunes lacked wing folding and took up a lot of space. When not spotted for takeoff at the rear of the deck (the angled deck had yet to be retrofitted to the Midway-class), the Neptunes were parked on the forward deck but their size meant that only the port catapult could be used the carrier air wing. Needless to say, many carrier captains and CAGs despised the Neptunes! 

By 1952, the problems with the AJ Savage had been ironed out enough that they could assume the nuclear delivery role from the Neptunes. While the Savage was smaller with wing folding and could return to the ship, their large size still had them universally disliked as they got in the way of flight deck operations. The Savages, though, could operated off the smaller Essex class ships, which expanded the number of available carriers for nuclear deterrent patrol. One of the reasons the Midway-class ships didn't participate in the Korean War was that they were needed in the Mediterranean for deterrent patrols. The P2V-3Cs were reconfigured to P2V-3Bs and sent ashore to act as training aircraft for the crews bound for the AJ Savage. The Neptune's role as an interim nuclear bomber was brief, less than two years, but it gave the Navy valuable experience in not just operating large aircraft from carriers but also with nuclear weapons handling. 

Source: Strike From the Sea: US Navy Attack Aircraft From Skyraider to Super Hornet 1948-Present by Tommy H. Thompson. Specialty Press, 2009, pp42-56. "Naval Aviation Centennial: Neptune's Atomic Trident (1950)" US Naval Institute Blog, 6 February 2011. Photos: 

10 August 2015

Canada's Nuclear Strike Force: 1st Air Division 1964-1972

Canada's CF-104s wore bare metal with white wings in the nuclear strike role.
For eight years, Canada maintained a small, but potent, nuclear strike force in Europe equipped with license-built Lockheed F-104 Starfighters under the auspices of the 1st Air Division. The 1st Air Division was established in 1952 in France as part of Canada's NATO air defense commitment. Four wings made up the 1st Air Division and each wing had three squadrons. For most of the 1950s, the Air Division was flew F-86 Sabres which were then replaced by CF-100 Canucks to provide all-weather/night air defense capability. In the late 1950s, Canada embarked on a search for a supersonic replacement for the CF-100 fleet. At the time, air defense was on Canada's mind but the political winds of the Cold War were such that as one of the charter members of NATO, considerable pressure was brought on Canada to contribute to the nuclear deterrent forces in Europe. With a generous industrial offset, the Lockheed F-104 Starfighter was chosen as the replacement aircraft for the 1st Air Division with the aircraft being license built by Canadair in Montreal as the CF-104. Originally the designation was to be the CF-111, but it was quickly decided to adopt the CF-104 designation to simplify administrative matters as some of Canadair's production would also be for NATO partners to augment European license production of the Starfighter. Coinciding with the selection of the Starfighter, on 2 July 1959, Canadian Defence Minister George Pearkes announced that the 1st Air Division (which became 1 Canadian Air Division in due time) would transition from the air defense role to the strike/reconnaissance role but little mention was made about the adaptation of nuclear strike as one of the Division's primary tasks. 

Reorganization of the Division's assets as part of NATO's 4th Allied Tactical Air Force would put two squadrons assigned to each of 1 Canadian Air Division's four wings- 1 Wing based at Marville AB in France would have 439 and 441 Squadrons, 2 Wing based at Groestenquin AB in France would have 421 and 430 Squadrons, 3 Wing based at Zweibrucken in West Germany would have 427 and 434 Squadron and 4 Wing based at Baden-Soellingen also in West Germany would have 422 and 444 Squadron. Following France's withdrawal from NATO military command in 1967, 1 Canadian Air Division was reorganized again with just three wings all based in West Germany- 1 Wing at Lahr, 3 Wing at Zweibrucken, and 4 Wing at Baden-Soellingen. 

The acquisition of nuclear weapons by the 1 Canadian Air Division was part of a broader umbrella agreement signed with the United States by the government of Prime Minister Lester Pearson. Interestingly the acquisition of nuclear-capable platforms like the Starfighter was made by the previous administration, that of Prime Minster John Diefenbaker. Pearson and the Liberal Party had scored political points attacking Diefenbaker for shifting Canada towards a nuclear-capable defense policy, but after defeating the Conservative Party in the 1963 elections, one of Pearson's first acts was to reverse the Liberal Party's course and actually acquire nuclear weapons. His change of heart occurred during the run up to the national elections and as an interesting historical side note, future Canadian prime minister Pierre Trudeau temporarily left the Liberal Party in disgust during this period of policy upheaval for the Liberal party. On 16 August 1963, an agreement was finalized and signed with the United States that provided for nuclear weapons for four weapons systems- the CF-104 Starfighters in Europe along with Honest John short range ballistic missiles for the Canadian Army in Europe as well as BOMARC missiles and Genie nuclear-tipped rockets for the CF-101 Voodoo force for the air defense of Canada. While a full analysis of the change in position by Prime Minister Pearson and the Cabinet is beyond the scope of this article, it primarily hinged upon improving the bilateral relationship with the United States, raising Canada's military posture within NATO, and a desire for a more effective defense policy. Given that the agreement was signed in the wake of the Partial Test Ban Treaty, the Canadian government did much to minimize the military's new nuclear role- for the Starfighter force, it wasn't until 1990 that the true extent of the 1 Canadian Air Division's nuclear capability was known. Some military officials went as far as to publicly point out to the Canadian press that the CF-104 was "too small" to carry a "large" nuclear weapon and it was a fighter, not a strike aircraft. 

Canadian officials inspect a CF-104. Note the faired over gunport.
In fact, the CF-104s were optimized for the nuclear strike mission- unlike most other nations' Starfighters, the Canadians didn't have the M61 Vulcan cannon installed and added an additional fuel cell in its place to extend its combat radius. The skill set and tactics for nuclear strike in Europe were also applicable to low level reconnaissance, so the CF-104s also could carry a centerline VICON camera pod that had 70mm cameras that photographed targets of interest on each side of the aircraft, straight down, and ahead. In the nuclear strike role, the wingtip fuel tanks were augmented by under wing fuel drop tanks with the nuclear weapon mounted on the centerline station. Three different nuclear stores were used by the CF-104 fleet and each had its own unique Canadian designation. The most common weapon was the B28 which came in two versions- the B28EX (which the Canadians referred to as "Weapon #1) which was a free fall weapon and the B28RE ("Weapon #2) which was a parachute retarded version of the B28EX. The B28 warhead was capable of different yields ranging from 70 kilotons to 1.45 Megatons,  but in practice only the 70 kt and 350 kt yields were used by the 1 Canadian Air Division.  A four digit code was required for the permissive action link (PAL) to arm the weapon. The B28EX was delivered in an over the shoulder toss while the B28RE was delivered at low altitudes, the parachute allowed the CF-104 pilot to make his escape before detonation. 

The B43 nuclear bomb (referred to by the Canadians as "Weapon #3") was only used by 4 Wing and it had a massive 1 Mt warhead and had the option of being parachute retarded and like the B28s, also had a PAL for arming. The fourth nuclear store used by the CF-104 force was the B57 and was a low-yield weapon with an explosive force of 5-20 kilotons. The B57 ("Weapon #4) was much lighter than the other stores as it was developed for the US Navy who wanted a lightweight tactical nuclear weapon. Like the other weapons, the B57 had an option for parachute delivery and also had a four-digit PAL code to arm the warhead. 

Kit box art showing the four tank configuration of the CF-104.
The B28 weapons were delivered first, starting in May 1964. The B57 was next to arrive in 1966 and the B43 was the last to arrive at Canadian bases in 1968. Because the weapons remained in US custody even on Canadian bases, it gave the Pearson government political cover that it wasn't contributing to proliferation. At each base the weapon storage area was manned by USAF personnel and the PAL codes were kept in a safe at the quick-reaction area (QRA) which was accessible only by the USAF alert duty officer. Release of weapons was under dual-key authority in which both US and Canadian command authorities had to provide authorization. Loading of a live weapon took about 30 minutes, so each Canadian base had a QRA area where fully-armed Starfighters stood nuclear alert. Double barrier fencing surrounded each QRA area and no individual could work on the alert aircraft alone- two personnel had to be present for even the most minor of tasks to be done to the QRA Starfighters. 

CF-104 in flight showing the white wings and large roundels.
The targets of the 1 Canadian Air Division consisted primarily of the logistical depots and airfields of the Group of Soviet Forces in Germany (GSFG). Major bridges that would be used in the event of a Warsaw Pact invasion of Western Europe were also on the Canadians' target list. The exact targets to be hit were provided by Supreme Allied Command Europe (SACEUR) HQ, but it was up to each squadron and its pilots to plan the inbound and outbound routes to the targets and any particular tactics to be used during the mission. Each squadron had a target evaluation board which would review each mission plan for acceptance. Once accepted, it was forward to the headquarters of the Strategic Air Command in Omaha, Nebraska, where it was included in the Single Integrated Operations Plan (SIOP), which was the US military's nuclear war plan. This way Canadian missions (and any other mission planned by NATO allies or other US military branches) could be deconflicted. This meant a high degree of timing precision was needed, typically inside of a 30 second window to hit each navigational waypoint to avoid flying into someone else's thermonuclear detonation. In practice missions, the Canadian pilots proved to be highly skilled, usually hitting each navigational waypoint within 10 seconds of the plan. Once fully operational in the nuclear strike role, the 1 Canadian Air Division was responsible for 20% of the 4th Allied Tactical Air Force's nuclear muscle- 4ATAF covered central and southern West Germany and included two Luftwaffe divisions, the USAF's Seventeenth Air Force, and a large number of Army air defense units. The squadrons of the 1 Canadian Air Division were subject to each and everyone of the nuclear inspection and readiness drills that any nuclear-capable USAF unit had to not just endure, but pass with near perfect scores. 

Prime Minister Lester Pearson's 1968 announcement that he planned to step down (and would be succeeded by Pierre Trudeau) coincided with a drawdown of Canada's NATO nuclear commitment. The social changes going in both Canada and the United States in the late 1960s required more focus on domestic issues in Canada and nuclear alert duty in Europe was quite expensive. Despite some of 1 Canadian Air Division's squadrons being operational with nuclear weapons for a short period of time (1 Wing only started nuclear alert duties in 1969), the drawdown began in 1970 with the last nuclear alert being stood on 31 December 1971 by 4 Wing. The last of the weapons were removed from the Canadian bases in 1972 as the Starfighter force was re-tasked with tactical air support- not only did the CF-104's get the M61 Vulcan cannon installed, they also were given a two tone dark gray/dark green camouflage as part of their new conventional tasking. 

The following message was sent from Canadian Forces HQ in Canada to the head of the 1st Canadian Air Division on 17 January 1972: 

"Final phase out of special weapons on 12 January marked the end of an era which started in 1964. Thank you for the great credit which you have brought to the Canadian Armed Forces in Europe."

Sources: Canadian Nuclear Weapons: The Untold Story of Canada's Cold War Arsenal by John Clearwater. Dandurn Press, 1998, pp38-61, 130-219. Additional information from Starfighter CF-104 by Anthony L. Stachiw and Andrew Tattersall. In Canadian Service Aircraft Series #4, Vanwell Publishing, 2007. Photos: Wikipedia, Aircraft Resource Center forums, RCAF Starfighter Association.

05 August 2015

The Four-Course Radio Range: Birth of the Modern Federal Airway System

This DC-6 captain uses headphones for navigation as well as communication
In the early 1920s, flying long distances was, for the most part, a fair weather enterprise. Even though airway beacon lights were being established for night flying across the United States, you still needed good visibility to fly at night. The explosive growth of the radio industry during this time frame facilitated the development of radio navigation. The origins of the four-course radio range lay just before the First World War, when engineers at the German electronics firm Lorentz proposed using radio signals in an overlapping pattern- one station broadcast the Morse code for A which was dot-dash or beep-beeeeeee and the other station broadcast the Morse code for N (since it was the inverse of A) which was dash-dot or beeeeeeee-beep. If you were in the overlap area, the broadcast of the A and the broadcast of the N would sound like a steady tone and then, depending upon how far left or right you were of the overlap, you heard a stronger A or a stronger N. If you were completely in the broadcast area of one or the the other, then you only heard the A or the N. The overlap area defined a straight line course either away or towards the broadcast station. This way, radio beams could define navigational courses. A variation of this system was used by German zeppelins for navigation during their bombing missions against London during the First World War. With an environment of extreme fiscal austerity in Germany during the war, continued development of the Lorentz radio range system moved to the United States. 

Diagram showing a Four-Course Radio Range
On 1 July 1925, the US Post Office inaugurated the first regular night air mail service which connected Newark, New Jersey and Chicago, Illinois. Beacon lights marked out the route between the two metropolitan areas, but it was quite obvious that what was needed was a system that operated day and night regardless of visibility conditions. Considering that air mail flights and the developing airline industry rarely flew over 10,000 feet, it didn't take much cloud cover make the airway beacons as well as daytime visual navigation useless. Despite the obvious benefits to the US Post Office and the movement of air mail, it was the US Army that took the lead, partnering with the National Bureau of Standards to develop the Lorentz system further. A four-course layout was used and utilized well-known technology already used by the radio broadcast industry. There were four quadrants, each opposing quadrant broadcasting a Morse code A or N, this way the there were four overlap regions and these four overlap regions defined the four courses. As long as a pilot heard a steady tone, he was on course flying within one of the overlap areas. The only equipment aircraft needed was a receiver and the pilot would tune into each successive station and listen for the tones from the ground station. A four-course radio range (or AN range) had a third identifier which was the station's call sign which was transmitted every 24 seconds as a verification you were using the right AN range station. The station's call sign was a three-letter code that was typically that of the nearest airport- like "DEN" for the AN range station in Denver. Every 15 minutes the broadcast of the A or N was interrupted for a voice weather report for the area. Special weather bulletins would interrupt the AN broadcast as needed. Three different terms are interchangeably used to refer to this radio navigation system- four-course radio range, AN range, or LFR, for low-frequency range. I'll be using primarily AN range in this article. 

Typical layout of an AN radio range station
Ground stations would be built at certain intervals to mark out airways. The first AN range stations had four antennas linked by wires to a central antenna and "radio shack". As the technology and transmitting requirements increased, the four antennas were towers of their own with the central tower responsible for the special broadcasts. The development and testing of the AN range system was completed in February 1928 with a demonstration of radio navigation flight from Newark/New York to Cleveland, Ohio, using three AN range ground stations- one in New Brunswick, New Jersey, one in Bellefonte, Pennsylvania, and the third one in Cleveland, Ohio. The Bellefonte AN range station was transferred from the National Bureau of Standards to the Aeronautics Branch of the Department of Commerce (this branch ultimately years later would be come the FAA) with the other two stations soon to follow. Revenue flights on the Newark/New York to Cleveland airway by AN radio range commenced in November 1928. Because of the budget constraints of the day, airway beacon lights were still being installed as they were considerably cheaper than AN range ground stations. It wasn't until 1933 that the construction and activation of AN range ground stations took precedence over the airway beacon lights. Despite the Depression-era fiscal austerity, enough AN range stations were built to permit radio navigation flight as far west as Omaha, Nebraska, just in the first year of the AN range system operation. Chicago and Boston were added by 1930 and that same year, an AN range station was built in Key West, Florida, to allow radio navigation to Havana, Cuba. By 1931, the pace of AN range station construction reached a point where it was possible to fly from New York to San Francisco by radio navigation only. At the outbreak of the Second World War, there were 90 AN range stations in the United States that marked out over 18,000 miles of airways. 

Marker beacons were also added to increase navigational accuracy along any of the four courses of a given AN range station. In order to have some semblance of order and a reasonably navigable airway, some AN range stations had their four courses deviate from exactly 90 degrees to each other. Looking at the map above, you might even make out the roots of the current airways on modern aeronautical charts. Each station operated in the low to medium frequency range from 200 kHz to 410 kHz, but the US military operated some of its own AN range stations that went up as high as 536 kHz. Since the technology used in the aircraft receiver and in the broadcast equipment in the AN range stations was based on that used in consumer radio sets and the radio broadcast industry, it was relatively inexpensive and adaptation by the aviation interests in the United States was rapid.
The AN range stations of the United States in 1950- you can see the origins of the current federal airway system
(click for larger image)
Despite the relative low costs and simplicity of the AN range system for airways navigation, there were several issues that were constant challenges to air crews. The first one was the layout of the AN range broadcast area- there were only four possible courses since there were only four overlap areas where a pilot could hear a steady tone instead of the A or the N. As can be seen from the map of the United States AN stations in 1950 above, there was some deviation from 90 degrees, but the practical limit was that the courses had to be separated by more than 20 degrees or the overlap area was simply too big to be of any navigational use. The second draw back was that there was no way of determining position location with the AN range system except if you were directly above the AN station in its "cone of silence". There were a series of complex procedures that had to be learned to intercept an on-course beam and to identify that beam- it involved a series of maneuvers while listening to the relative strengths of both the A and N signals. Changes in the signal strength while performing a series of maneuvers determined which quadrant you were in as well as which on-course beam you intercepted. Now imagine having to do this in a very noisy prop liner flight deck in inclement weather!

Typical AN range on a chart, this is in the Mojave Desert SW of Las Vegas
The primary drawback of the AN range system was a matter of physics. The longer radio wavelengths used were prone to static interference from thunderstorms and heavy precipitation and at night, (what's called "night effect") propagation of the radio signals went farther due to the ionosphere which meant it was possible for two AN stations normal out of range of each other to interfere with each other's signal at night. This distance deviation can range anywhere from 30 to 60 miles and was more pronounced on AN range frequencies above 350 kHz. The ground conductivity around the AN station could also affect the signals and any location where there was an abrupt transition from land to water could experience what's called "shore effect" where the radio waves get bent off course. This was most pronounced on on-course beams that ran parallel to a nearby shoreline. Terrain also had a deleterious effect on AN signals, particularly in mountainous areas. The difference in ground conductivity of valleys versus mountains on each side of a valley could create false beams.

Technical improvements to the transmitting antennas made during the late 1930s and into the Second World War improved signal integrity to some degree, but the signals were still a longer wavelength prone to interference by natural sources- but more importantly, a better AN signal still left users with the limitations of a four-course layout. The AN range system was trickier for landing and was nowhere near the level of precision needed for a true low-visibility approach into an airport. The four-course layout meant that not every airport let alone their runways were aligned along one of the on-course beams and at a distance of 30 miles from the AN range station, the on-course beam was 2 miles wide. "Instrument landings" to use the term loosely were still possible at select airports, but not widespread enough to be of significant utility to the growing number of users in the federal airway system of the day. A variety of programs started in the late 1930s focused on using shorter radio wavelengths as they were much less prone to natural interference and were not limited to just a four course layout. That radio wavelength today we know as VHF- RCA, the Radio Corporation of America, led the development of VHF transmitting equipment for navigational use. Because a VHF station wasn't limited to just four courses like the AN range, it was called VHF Omnirange, or VOR. The first test VOR installation went live in 1940 at Weir-Cook Airport in Indianapolis, Indiana (today's Indianapolis International Airport). The other VHF navigational initiative that grew out the work to find something better than the AN range system was the ILS, instrument landing system- the development of VOR navigation and ILS will be the subject of a future blog article and is beyond the scope of this feature.

Following the Second World War, more VOR stations were established, displacing many of the AN range stations. Quite a few AN range stations were converted to NDB stations- the central tower was all that was needed, so the four outer AN towers were removed. But the simplicity and low cost of AN range stations meant that they persisted well into the 1970s and early 1980s. The last American AN range station was in Alaska and one source on a radio hobbyists' forum indicated that this occurred around 1971 with the the last AN range station in Canada located in British Columbia decommissioning in the early 1980s. One example of an AN range station converted to an NDB was the Spokane, Washington, AN range station. In 1936 it operated at Felts Field at 365 kHz which was Spokane's original commercial airport until replaced by the former Geiger AFB in 1946. In the early 1950s the AN range station was moved to the town of Marshall, southwest of Spokane, to better serve the new airport at Geiger Field (now Spokane International Airport) but it kept the same frequency at 365 kHz. It was one of the AN range stations that was converted to an NDB station when the AN ranges were replaced by VOR stations. In the late 1980s the Marshall NDB, still at 365 kHz, was moved back to Felts Field which had become a general aviation airport. In 2008, the NDB there was moved to Deer Park Airport north of the city, still operating at 365 kHz to this day. That would mean that next year, there has been a radio navigation aid in the Spokane area of one form or another operating at 365 kHz for ninety years!

Sources: Electronics in the Evolution of Flight by Albert Helfrick. Texas A&M University Press, 2004, pp 36-42, 54-57. "Flying the Beam: LF/MF Four-Course Radio Ranges" by Richard Harris, 2013, 2014 at http://home.iwichita.com/rh1/hold/av/stories/avionics/radiorange.htm. "Aviation Low-Frequency Radio Ranges" at ed-thelen.org. Photos: Wikipedia, FAA, Houston Municipal Airport Museum at 1940airterminal.org.