Refining Anti-Submarine Warfare: The Grumman AF Guardian

Grumman XTB3F Guardian prototype
(San Diego Air and Space Museum)

By 1944, the United States was already laying down plans for the invasion of Japan and if the stiff resistance in the island hopping campaign across the Pacific was any indication, the Japanese were far from defeated and planners expected the worst may yet to come. Navy torpedoes delivered by Grumman TBF Avengers were notoriously unreliable and required a relatively slow approach of 120 mph during their drops at low level. Navy torpedo research languished in the years before the Second World War and torpedo bomber crewman paid the price in their lives. Wartime urgencies caused a reinvestment of torpedo development by the Navy. New air-launched torpedoes in the works could be dropped at higher speeds and further stand-off distances from enemy warships, but by this point in the war, in order to take advantage of the new designs, something with twice the engine power of the venerable Avenger was needed. The first design Grumman submitted for a new carrier-borne torpedo bomber was for the large XTB2F. With two Pratt & Whitney R-2800 Double Wasp radials, the XTB2F was a big aircraft with a maximum takeoff weight of nearly 43,000 lbs which was 8,000 lbs heavier than the maximum takeoff weight of a late model B-25 Mitchell medium bomber! The XTB2F reached the mock up phase before the program was canceled in June 1944 as it was simply too large of an aircraft for the Essex-class fleet carriers. 

The XTB2F mockup before the program cancelation
(Wikipedia/Grumman Archives)

Under the G-70 in-house designation, Grumman offered several variations of a new single-engined design, some of which were mixed-propulsion designs with a big radial engine (either the Wright R-3350 or the Pratt & Whitney R-4360) and a jet engine in the rear fuselage for extra speed on the target runs. When it became clear the R-3350 and R-4360 radials wouldn't be ready for the planned production schedules for what was designated the XTB3F, the Navy asked Grumman for a redesign with the more widely available Pratt & Whitney R-2800 engine which was the same engine used on the B-26 Marauder and P-61 Black Widow. A Westinghouse J30 would be installed in the rear fuselage- the J30 was the first all-American jet engine to run and was only the second production axial-flow engine in the world after the German Junkers Jumo 004. Using the R-2800 engine only cost the reconfigured XTB3F 30 mph of speed which was acceptable to the Navy. Despite the ending of the war by this point, the Navy still wanted the XTB3F, now named Guardian, as a replacement for the Avenger and on 23 December 1946, the prototype aircraft made its first flight. 

As designed, the J30 turbojet in the rear fuselage of the aircraft had 1,330 lbs of thrust and was fed by air intakes in the leading edge wing roots that fed ducts that ran to the engine. During ground test runs, the intake ducting wasn't big enough and strong enough to handle the mass flow to the J30 and would collapse. The engine was only run on ground tests and never used during the flight test program. Ultimately the intake duct problems resulted in the engine being removed and would be absent from the production Guardians. 

With a spacious weapons bay for the Navy's latest torpedoes, the Guardian also had two 20mm cannons in each wing as well as provisions for underwing bomb racks and rocket launchers. Most remarkable about the Guardian, though, was its size. It was the largest single engined piston aircraft to be operated from an aircraft carrier and was 2/3 the size of a Douglas DC-3. In fact, its production maximum take off weight was nearly that of a DC-3! The big R-2800 radial up front was canted down slightly to improve pilot visibility in the carrier approach pattern and it was also canted 3 degrees to the right to help offset the torque of the big engine. It's large tail was to help its stability in low altitude regimes but it did make the Guardian difficult to handle in a crosswind. 

AF-2S and AF-2W hunter/killer team
(San Diego Air and Space Museum)

On the day following the Guardian's maiden flight, the Navy imposed a stop-order on the program to give funding priority to the Douglas AD Skyraider and Martin AM Mauler programs which were also capable of dropping torpedoes and as optimized attack aircraft, were more flexible than the Guardian not to mention smaller in size. It might have been end of the Guardian had it not been for the rapid postwar expansion of the Soviet Union's submarine force. Navy carrier forces needed a specialized anti-submarine aircraft and the XTB3F Guardian best fit that need. As a result, in January 1947, the Navy redesignated the Guardian as the AF (this would be a whole topic for a complete article on how the Navy consolidated the scout, bomber and torpedo roles in the new "A for Attack" designator). Given the state of the art of anti-submarine warfare of the time, though, a single AF Guardian couldn't carry both the necessary detection equipment and weapons, so the Navy brought back the hunter-killer team concept that had worked well during the Battle of the Atlantic were Avengers hunted U-boats and were assisted in their attacks by F4F/FM-2 Wildcats. One Guardian would be equipped with the AN/APS-20 radar in a large under fuselage radome and this would be the AF-2W "hunter". The other Guardian of the pair would be the AF-2S "killer". In operational service, the AF-2W was nicknamed "Guppy" while the AF-2S was nicknamed "Scrapper". 

Interestingly the AN/APS-20 radar started out as a crash program to give the Navy its first airborne early warning aircraft to warn of incoming Kamikaze attacks. Fitted to an Avenger designated the TBF-3W under Project Cadillac, the first AEW Avengers were in Hawaii conducting carrier qualifications when the war ended in 1945. The radome and radar installation on the Guardian was for all intents and purposes, pretty much just moved over from the TBF-3W to the AF-2W. With the J30 engine and its intake ducting gone, space was available for the radar and electronics on the AF-2W and more fuel on the AF-2S. 

Production was launched in October 1947 with an order for 23 early examples which would be devoted to operational testing as well as further flight testing. The first operational examples were delivered to the fleet in September 1950 with VS-24 being the first ASW squadron to get their Guardians. The first carrier qualifications took place that November and in December 1950, VS-24 embarked on the USS Palau (CVE-122) on the Guardian's first operational cruise. Now imagine an aircraft as heavy as a DC-3 that's just 2/3 the size of a DC-3 operating off the decks of escort carriers like the Palau! While a tough and reliable aircraft, a significant number of AF Guardians were involved in deck accidents. Most deck crews were used to handing aircraft half the size of the Guardian and one ASW squadron commander got so frustrated at the incidence of handling accidents just moving the Guardian on the carrier that he required a pilot to be present and in the cockpit if needed when an AF was being moved, even if it was just in the hangar deck!

Operationally, the AF hunter/killer team would form a protective ASW screen around the carrier battle group with the idea to detect and attack any submarines as far away from the carrier as possible. During the Second World War, the protective ASW screen was handled primarily by destroyers and destroyer-escorts- with the arrival of the Guardian, aircraft could now provide the ASW screen for the task force. Guardian teams would fly up to 500 miles out from the carrier with the AF-2W "Guppy" flying a search pattern using its radar to either detect a surfaced sub or a snorkel. Once detected, the "Guppy" would summon the AF-2S "Scrapper". Once in the area, the AF-2S had it's own pod-mounted radar under the right wing (and a search light under the left wing if it was needed at night) to prosecute the attack using vectors from the "Guppy". A periscope sight aft of the wings in the belly was used to release depth charges. If needed, the "Scrapper" could come back around and use rockets and bombs to finish the job. Late model Guardian "Scrappers" designated AF-3S were fitted with magnetic anomaly detection (MAD) gear to improve the chances of note just detecting a sub but sinking it. 

A total of 386 Guardians were built and from 1945 to 1954, it was the US Navy's premier front-line carrier-based ASW aircraft. Of that nine year span, only three of those years was the Guardian truly operational as part of anti-submarine squadrons at sea. Its replacement, also from Grumman, the S2F Tracker, would combine the hunter and killer roles in the same aircraft and the design of the Tracker was heavily influenced by the canceled XTB2F, the design that was replaced by the AF Guardian. Of all the Guardians built, five survived and were used by Aero Union as 800-gallon capacity water/retardant bombers against forest fires from 1957 to 1974. That final year the US Forestry Service instructed its water bomber operators that single engined aircraft could no longer be used. Most were scrapped but a single Guardian was saved and restored to its original configuration and is now on display at the Naval Aviation Museum in Pensacola, the last of its breed in existence. 

Sources: Ironworks: The Story of Grumman and Its Aircraft by Terry Treadwell. Tempos Publishing, 2000, p150-154. "Grumman's Guardian" by Budd Davison. Flight Journal, September 2011.

When America Needed a Hero, Butch O'Hare Stepped Up

Following the attack on Pearl Harbor, the first six months of 1942 were dark days for the American public. The Japanese war machine seemed unstoppable with the fall of the Philippines, Burma and Singapore. The Dutch East Indies and the Solomons would also fall. Japanese air attacks had already taken place on Darwin, Australia. A Japanese sub even managed to surface off the coast of California and shell targets on the coastline. Rommel's Afrika Corps were pushing steadily eastward towards the Suez Canal. The German U-boat offensive in the Atlantic was taking a tremendous toll on shipping.

The Japanese had landed on New Guinea and with the establishment of a major base in Rabaul in the Solomon Islands, Australia's populous east coast could fall under striking range. Already the carriers Enterprise and Yorktown had conducted a diversionary raid in the Marshall Islands and it was left to the carrier Lexington to make a diversionary raid several weeks later against Rabaul. On 20 February 1942 the Lexington was steaming 400 miles northeast of Rabaul when the Grumman F4F Wildcat fighter squadron VF-3 led by Lt. Commander John Thach was scrambled to intercept a Kawanshi H6K "Mavis" flying boat that had spotted the carrier strike force. Despite shooting down the flying boat, the position of the Lexington had been given away and later that afternoon, a formation of nine Mitsubishi G4M "Betty" bombers approached the carrier at 11,000 feet. Despite the shootdown of four of the bombers by the Lexington's combat air patrols, five of the bombers made a level bombing run against the carrier. Waiting until the bombs had been released before making sharp turns, the Lexington escaped damage. Unfortunately, a second flight of nine G4M bombers approached and this time only two of the Lexington's F4F Wildcat fighters were in a position to intercept the incoming Bettys. One of those Wildcats was flown by Lt. Edward H. "Butch" O'Hare. 

O'Hare firewalled his Wildcat and made directly for the bomber formation that was only minutes away from their bomb run on the Lexington. The Betty had a 20mm cannon tail gun and four machine gun defensive positions. Well-known for his marksmanship, on O'Hare's first pass of the V-shaped formation, two bombers fell to his guns. He then pulled the Wildcat into a tight turn for another pass at the formation and downed three more bombers, all of this action taking place in sight of the sailors onboard the Lexington. O'Hare's commanding officer, John Thach, joined the fight and downed several more bombers before scattering the formation as it beat a hasty retreat from the vicinity of the Lexington. In the space of only four minutes, Butch O'Hare become the first US Navy ace, saving the Lexington in the process. According to Thach, O'Hare had expended only sixty rounds of 0.50-caliber ammunition in the process! The captain of the Lexington, Frederick Sherman, recommended O'Hare for the Congressional Medal of Honor for his actions that day- O'Hare had refused, insisting to his captain that any one of his squadron mates would have done the same thing. But with the raid on Rabaul called off due to the loss of the element of surprise and the constant stream of bad news arriving from the Pacific and Europe, O'Hare became an instant hero- he was young, dashing, and was the recruiting poster boy for naval aviation. He was summoned to the White House in April 1942 by President Franklin D. Roosevelt to receive the Medal of Honor. 

In June 1942 O'Hare relieved Thach as the skipper of VF-3 and the following spring the squadron swapped designations with VF-6 as O'Hare converted to the more powerful Grumman F6F Hellcat. Embarked on the USS Independence with future ace Alexander Vraicu as his wingman, O'Hare would add to his score with several more victories during operations against Wake Island. Following action over Wake Island, O'Hare was promoted to be the new CAG (commander air group) for Air Group 6 aboard the USS Enterprise. At the time the Navy was concerned about single or dual aircraft attacks at night when the carrier battle group's defenses were at their most vulnerable. O'Hare had come up with an innovative idea to use a radar-equipped Grumman TBF Avenger orbiting over the carrier at night. On each wing of the Avenger would be Grumman F6F Hellcats who would be cued into the night intruders by the crew of the Avenger. 

On 26 November 1943 O'Hare took up one of the Hellcats along with the radar-equipped Avenger and a second Hellcat to patrol the dark skies over the Enterprise. With some initial difficulties getting the formation coordinated with incoming bombers detected on radar, Butch O'Hare's Hellcat would slide out of the formation that night and disappear. It had been thought for years that he had gotten caught in the crossfire between the Avenger's gunner and Betty bomber and was hit inadvertently by the Avenger's gunner. However, later research that involved interviews with the surviving crew members of that formation indicate that O'Hare most likely had been downed by a lucky shot from a Betty gunner. Though declared missing in action, he was declared dead a year later. In his honor in 1947, Orchard Depot Airport in Chicago was renamed O'Hare Airport and its prior name is the reason why O'Hare's three letter code is ORD. In Terminal 2 of Chicago O'Hare is a restored Grumman F4F Wildcat painted in the colors of Butch O'Hare's aircraft during his Medal of Honor mission. 

As an interesting historical side note, O'Hare's father "Easy Eddie" O'Hare was known as Al Capone's lawyer in the 1920s. Urban legend has it that a crisis of conscience in teaching his son Butch about right and wrong led the elder O'Hare to turn informant on Capone that led to the gangster's imprisonment on tax evasion charges. However, it may have been more a matter of survival for the elder O'Hare as he had offered to meet with the IRS after the 1929 St. Valentine's Day massacre in which rival gang members were brutally executed. O'Hare turned over extensive records that helped convict Al Capone in 1933. In November 1939, Eddie O'Hare was on his way home from the dog track when he was gunned down and killed in his car in a murder that to this day remains unsolved. 

The following is from Butch O'Hare's Medal of Honor citation: 

"For conspicuous gallantry and intrepidity in aerial combat, at grave risk of his life above and beyond the call of duty, as section leader and pilot of Fighting Squadron 3 on February 20, 1942. Having lost the assistance of his teammates, Lieutenant O'Hare interposed his fighter between his ship and an advancing enemy formation of 9 attacking twin-engine heavy bombers. Without hesitation, alone and unaided, he repeatedly attacked this enemy formation, at close range in the face of intense combined machine gun and cannon fire. Despite this concentrated opposition, Lieutenant O'Hare, by his gallant and courageous action, his extremely skillful marksmanship in making the most of every shot of his limited amount of ammunition, shot down 5 enemy bombers and severely damaged a sixth before they reached the bomb release point. As a result of his gallant action—one of the most daring, if not the most daring, single action in the history of combat aviation—he undoubtedly saved his carrier from serious damage."

Source: United States Naval Fighters of World War II in Action by Michael O'Leary. Blandford Press, 1980, p58-62.

Two Paperclips and an Eraser Contribute to Victory in WW2

The first variants of the Navy's premier carrier-borne fighter of the first half of the Second World War, the Grumman F4F Wildcat, were hampered by one weakness even before they took off from their aircraft carriers- lacking a folding wing, the first versions of the Wildcat took up quite a bit of space on the carrier and, by extension, that limited the number of Wildcats that could carried aboard. Given combat losses that would inevitably occur, having as many aircraft on the carrier as possible conferred tactical advantages in battle. The current production version of the Wildcat at the time was the F4F-3. 

The most obvious answer would be hinge the wings' outer sections and folding them upward as was done on most carrier aircraft (even to this day). However, to Leroy Grumman and his engineering team, that wasn't an optimal answer as that increased the height of the stowed aircraft- if the wing could be folded in a way that didn't increase the height of the aircraft, then extra aircraft could be winched up and stowed up near the ceiling of the hangar deck. Grumman reasoned that the optimum geometry would be to somehow fold the wing back not unlike the way a bird folded its wings back along its body. Grumman drew upon his engineering intuition and reasoned that the wing had to rotate about a pivot point. He took a draftsman's eraser and two paperclips; he bent one end of the paperclips and began to stick them into the eraser. The eraser was the body of the Wildcat and the paperclips were the wings. By trying different angles, Grumman managed to figure out the angle needed to that when the clip was rotated, it folded back flat against the eraser. This was known in engineering parlance as a skewed axis. 

In the Wildcat, this axis was a pivot set into the wing root that pointed outward and backward at angle into the moving portion of the wing. As the wing rotated about this pivot, it folded back against fuselage, making the F4F a compact package- so compact, that six F4Fs with what Grumman called the "Sto-Wing" could fit into a deck or hangar space normally occupied by two F4Fs that had nonfolding wings. At first it was planned to use hydraulics to fold the wings, but it was found this added excessive weight, so the wings would have to be folded manually by the deck crew. A large master pin would lock the wing in position either extended or folded.

The Sto-Wing was immediately placed into the production line- with the current Wildcat model being the F4F-3, those with the Sto-Wing became the F4F-4. From a tactical standpoint, an aircraft carrier could now carry twice as many F4Fs as before with the wingspan of the Wildcat going from 39 feet to just over 14 feet folded. Deck handling improved as it was easier to move an F4F with the wings folded on a crowded flight deck or in a packed hangar deck. The Sto-Wing concept was applied as well to the TBF Avenger and the F4F Wildcat's successor, the F6F Hellcat. And it's seen today on carrier decks with the Northrop Grumman E-2 Hawkeye- since the E-2 had the dish-like radome above the fusleage, the wings couldn't be folded up and over each other as was done on other long-span carrier aircraft like the Lockheed S-2 Viking. So E-2 Hawkeye's wings use the Grumman Sto-Wing principle to fold back towards the tail.

Source: The Grumman Story by Richard Thruelsen. Praeger Publishers, 1976, p124-125.

The Groundbreaking Gun Turret of the TBF Avenger

On 8 April 1940 the US Navy ordered two prototypes from Grumman for a multirole torpedo bomber to replace the antiquated Douglas TBD Devastator. With Grumman having well-established credentials in designing tough carrier-based fighters, what would be come the TBF Avenger had a remarkably smooth development period due to the experience built up in designing and producing the same company's F4F Wildcat fighter. Their biggest single-engine carrier-based aircraft to date, a fully-loaded Avenger was twice as heavy as two Wildcats. But one of the Avenger's most significant technical innovations also happens to be one of the least-known features of the aircraft. 

At the time the Avenger was ordered by the US Navy, few aircraft in any nation's service worldwide used gun turrets as most defensive guns were trained manually on gimbaled mounts through open hatches and windows. The gun turrets that were in existence used either mechanical or hydraulic systems to rotate the turret in azimuth and to raise or lower the gun in elevation. Mechanical systems used wheels and brakes operated by the gunner and hydraulic turrets used the same systems as mechanical systems but with the addition of hydraulic power to lessen the physical effort needed by the gunner to track and engage targets. Neither system was satisfactory for Grumman's engineers and combat use showed that the systems were either too slow or too heavy for use on a single-engined carrier-based torpedo bomber. The Navy asked Grumman for a more responsive system that was also lightweight. 

Leroy Grumman turned over the challenge to the first electrical engineer hired by the company, a young ex-General Electric engineer named Oscar Olsen. Grumman assigned him the challenge of developing an electrically-driven system for the Avenger's gun turret. The challenge was bigger than it seemed- depending upon the flight attitude of the aircraft, different sides of the circumference of the turret would present different loads to any drive system resulting in differing speeds which would adversely affect target tracking. For instance, if the Avenger were in a dive, and the turret was rotating to engage an enemy aircraft, one side of the turret is rotating downward and has less of a load on the motor than the opposite side that is rotating upward against gravity and thereby presenting more of a load on the motor. 

Olsen fell back on his experience with GE and looked at what were called amplidyne motors. These were electrical motors in which both the speed and torque of the motor can be controlled. Olsen knew that GE had made them for the construction industry where two motors were used to lift up a bridge span. Being on opposite ends of the span, it was important to have absolute control over both the speed and torque of the motors winching up the span. GE also made amplidyne motors for the steel industry to wind up the steel sheet used to make tin cans. As the flattened sheet comes out of the furnace, the tension has to kept within a narrow range or the sheet sags, or worse, breaks. Amplidyne motors were used to spool up the steel sheet- as the roll got bigger and heavier, the torque could be increased but the speed controlled to maintain the same amount of tension on the steel sheet. Olsen figured out that a set of amplidyne motors synchronized with an electric circuit would allow the Avenger's gunner to smoothly and quickly move the turret with just fingertip controls. 

Olsen paid a visit to his old engineering colleagues at GE's research facility and explained what he needed and why he needed it. In a short period of time, GE produced by hand several prototypes of a small but powerful amplidyne motor that were installed and successfully tested on the TBF Avenger prototypes, proving the electrically-powered amplidyne motor-driven turret to be superior in all respects to both mechanical and hydraulically-driven gun turrets. The gun turrets on many different combat aircraft subsequently were patterned on the amplidyne motor-driven system devised by Oscar Olseon and pioneered in operational use by the TBF Avenger. 

Source: The Grumman Story by Richard Thruelsen. Praeger Publishers, 1976, p116-124.