A Watershed Moment in Close Air Support: The 1927 Battle of Ocotal

Major Ross Rowell, USMC

Less than a year had elapsed in Nicaragua since the last civil war and American intervention (1912-1925) ended when liberal and conservative factions in the unity government broke into open rebellion on 2 May 1926 with conservative factions representing the Managua government. On 24 January 1927, the 400 Marines arrived in-country at the request of the government as events proved beyond Managua's ability to control. Accompanying the initial group of Marines was the Marine Observation Squadron VO-1M, led by Major Ross Rowell. In the years following World War I, Marine aviation was very much a lean force, so much so that Marine aviators like Rowell had to be temporarily assigned to the Army to get flight training. Rowell's tour of duty with the US Army began in 1923 at Kelly Field in San Antonio, Texas. There he was assigned to the 3rd Attack Group, an Army squadron that had been established in 1921 to specialize in ground attack. The unit had experimented with a variety of aircraft during this period which were to have been designed for the role of ground attack (and distinct from long-range bombing) on the battlefield, but most designs were wholly inadequate for the roles envisioned by the Army unit. The unit ended up experimenting with the De Havilland DH-4B for ground attack as the aircraft was plentiful, available, and had been used by the British in the ground attack role in the First World War. Using the DH-4B, the unit experimented with dive bombing, which to be more accurate was more glide bombing- the distinction being that glide bombing involved descents of about 45 degrees while dive bombing was quite a bit steeper, approaching 70 degree or more. British experience in the First World War had shown that steep attacks greater than 45 degrees were needed to attack ground positions and while ground attack in the First World War never proved decisive, the seeds of the idea had been planted and were being sown further by the unit that Major Ross Rowell was assigned to. Their DH-4Bs were modified with underwing racks that could hold 10 small bombs. The aircraft was less than suitable for the role and the unit's work had concluded that attacking aircraft would be exposed to hostile fire during its attack that the mission would be of little use. 

Despite the inadequacy of the DH-4 biplane, Rowell held the opposite view as a result of his time with the Army in San Antonio. Given the number of interventions the Marines were conducting in the 1920s, Rowell was convinced that an aircraft making a steep glide or dive attack would be useful for close air support in the small guerrilla wars that the Marine Corps were being committed to throughout Latin America during the interwar period. Upon his return to the Marines from his tour with the Army, Rowell was given command of Marine Observation Squadron One (VO-1M) based at North Island in San Diego. VO-1M had just returned from the Marine intervention in Santo Domingo and based on their experience there, was designated the aviation asset to accompany Marine expeditionary forces being sent overseas. As such, Rowell instructed the pilots of VO-1M in glide and dive bombing based on his experiences with the Army's 3rd Attack Group in Texas. He relentlessly trained his men against simulated ground targets as well as seaborne targets. In February 1927, VO-1M was given orders to deploy to Nicaragua to support the Marines there that landed the previous month. By the end of February, Rowell had the unit's DH-4B biplanes flying a variety of missions ranging from observation and reconnaissance, shuttling messages amongst the various Marine garrisons in the country, and supporting assaults against the rebels who called themselves Sandinistas after their leader, Augusto Cesar Sandino. Prior to the arrival of VO-1M, most air missions during the civil war were flown by the Nicaraguan Air Service which didn't amount to much- two converted civilian Laird Swallow biplanes flown by mercenary pilots that dropped dynamite on the Sandinistas. Needless to say, it wasn't terribly effective and for the most part, the Sandinistas ignored the aircraft until VO-1M arrived. 

Marine DH-4B. Note the Ace of Spades logo of VO-1M. 

On 17 July 1927, a large Sandinista force of 800 men attacked the small Marine outpost at Ocotal near the Honduran border about 125 miles from the capital, Managua. Defending the outpost were 37 Marines and less than 50 Nicaraguan National Guard. The attack opened at 3:00am and it wasn't until 10:15am in the morning that the Marine HQ in Managua became aware of the attack after a Marine patrol overflew Ocotal and saw the gunfire. Major Rowell mustered five DH-4Bs which were crewed by two and bombed up to fly to Ocotal. Since there was no other Marine force in the area that could be delivered to the area in time on account of distance and Nicaragua's primitive transportation network, it was Marine air or nothing to save the garrison at Ocotal. Arriving over the garrison, Rowell circled the area to assess the situation. At the time, radios were supplied to VO-1M, but their were so heavy given the technology of the time, it was easier to remove the radios and trade that weight for fuel and bombs. The beleaguered Marine garrison laid out colored panels to give Rowell and his pilots indications of where the Sandinistas were located. Being 125 miles from their base in Managua, the fuel situation didn't lend itself to extended loitering by the DH-4Bs and to make matters worse, thunderstorms were approaching the area. Rowell organized his pilots into a bombing column that was single file and he made the first diving attack from 1500 feet, released a some bombs and then pulled out at 600 feet with the other four aircraft in the column following suit against targets he'd marked with his own bombs. Since the Sandinistas' previous exposure to air attacks were minimal, the Marine attacks drew little if any ground fire. In fact, the Sandinistas weren't even taking cover. Rowell astutely realized this fact and had his men fly lower for greater accuracy, diving from only 1000 feet and pulling out at only 300 feet. During their dives, the pilots fired the forward gun to add to the firepower and in the pull out, the observer in the rear seat would strafe as well with their trainable gun, effectively suppressing any potential ground fire. The Sandinista attack on the garrrison was broken as they retreated in the countryside taking approximately 25% casualties from the air attacks. Major Rowell would earn the Distinguished Flying Cross for leading the attack to save the Marine garrison at Ocotal.

It was a watershed moment in the history of military air power and close air support- the 1927 Battle of Ocotal was the first time that an ground unit facing a numerically superior enemy was saved solely by aerial intervention. It was a lesson not lost by the Marines in particular. During the time period and well into the Second World War, Army doctrine manuals discouraged close air support out of a fear of friendly fire casualties while the Marine Corps were quite the opposite in seeing air support as an integral part of ground force operations. It was also the first time that steep diving attacks were used in combat effectively. During his time at North Island in San Diego, Rowell had made friends with a number of naval aviators of the Pacific Fleet would were soon to make their own mark on the history of military aviation with their use of dive bombing. But as always, that will be the subject of a future post on this blog!

Historical aside: VO-1M was formed in 1919 as First Division, Squadron 1. Following the intervention in Santo Domingo, the squadron was redesignated VO-1M. Prior to the Battle of Ocotal, the squadron was redesignated again as VO-8M. In 1934, as part of the reorganization of Marine aviation, the unit was reorganized and was routinely sent to sea aboard aircraft carriers to participate in exercises. In 1941 the unit was moved to Hawaii with their first monoplane, the Vought SB2U Vindicator, along with a redesignation to VMSB-231 (Marine Scout and Bombing Squadron 231) and was embarked on the USS Lexington when Pearl Harbor was attacked. In 1942 the squadron transitioned to the Douglas SBD Dauntless and participated in actions at Guadalcanal and later in the war got the Vought F4U Corsair for the Marshall Islands campaign. They were deactivated in 1962 after long serving as a Marine reserve unit. They were brought back in 1973 to become an AV-8A Harrier unit and fly the AV-8B Harrier II today as VMA-231 "Ace of Spades"- the Ace of Spades logo used on VO-1M's DH-4s in Nicaragua are still the unit emblem today.

Source: Strike From the Sky: The History of Battlefield Air Attack, 1911-1945 by Richard P. Hallion. Smithsonian History of Aviation Series, Smithsonian Institution, 1989, pp 71-75. Photos: USMC, Wikipedia.

The First Steps to a Turboprop Transport, Part Two

A week and a half ago I had blogged about how the USAF was getting turboprop transport experience by setting up a test squadron at Kelly AFB to operated transport aircraft that had been converted to turbine power: 

52-2693 and 52-2672 in flight together.

On 15 June 1954, the headquarters of the Military Air Transport Service (MATS) activated the 1700th Test Squadron (Turboprop) at Kelly AFB, Texas, with the task of developing maintenance procedures and techniques for the employment of turboprop transport aircraft pending the arrival of the C-130 and C-133 into the USAF service. The squadron had three flights with each flight dedicated to a single type for the testing of standard transport aircraft that had been converted to turboprop power. The first of the three flights to be activated would operate the Convair YC-131C. Two aircraft were converted from standard C-131 Samaritan transports (the USAF version of the CV-340 airliner) to use early test versions of the venerable Allison T56 turboprop.

Back in January 2010 I had written a short posting about the second of the demonstrator aircraft that were operated by the 1700th Test Squadron and operated in the second flight of the unit- the Boeing YC-97J, a Pratt & Whitney T34-powered version of the C-97 Stratofreighter. I had recently picked up Cal Taylor's voluminous tome on the Douglas C-133 Cargomaster and he devotes considerable space to the YC-97J and its operational use by the 1700th TS. The YC-97J made its first flight at Edwards AFB on 19 April 1955 and given that it used the same T34 engines as the upcoming C-133, the USAF was keenly interested in flight testing the engine in an operational environment with the YC-97J. From my previous posting about the YC-97J: 

Boeing converted two aircraft (52-2693 and 52-2672, both KC-97Gs) to turboprop power. Pratt & Whitney YT34 turoprop engines (which would later be used on the Douglas C-133 Cargomaster) delivering 5,700 horsepower were substituted for the four R-4360 radial engines. For a brief time the USAF considered redesignating these two Stratofreighters as C-137, but ended up assigning them the designation YC-97J (ironically the C-137 got used for the Boeing 707s used by the military, itself a development of the Model 367-80 prototype).

The conversion to turboprop power shaved nearly 5,0000 lbs off the aircraft's weight as the YT34s were much lighter but more powerful. The first flight was made on 19 April 1955 and the YC-97J demonstrated significant improvements in overall performance. The top speed was 417 mph compared to 375 mph for a regular Stratofreighter and the YC-97J took only 14 minutes to reach 20,000 feet whereas the regular Stratofreighter took 50 minutes!

Inflight study of the YC-97J during its Edwards flight test program.

In addition to using the same T34 engines as the C-133, the YC-97Js also used an early version of the same Curtiss turboelectric three-bladed propellers planned for the C-133. The first YC-97J completed its flight testing at Edwards and was delivered to Kelly AFB on 14 September 1955, nine months after the YC-131Cs had arrived. The second YC-97J arrived at the end of the month. After a short series of flights operating within the continental United States, the USAF authorized the aircraft to begin overwater missions with the first overwater flight being to Kindley Field in Bermuda- the aircraft covered the 1,700 mile route from San Antonio to Bermuda in 4 hours 42 minutes, the fastest time at that point by a prop-driven aircraft. On 26 January 1956, the YC-97J departed for Rhein-Main AB in West Germany staging through Dover AFB in Delaware, then Newfoundland and Scotland. Despite record breaking cold weather on the trip, the YC-97J performed flawlessly without any of the usual maintenance headaches that were commonplace for the piston-driven C-97s. On the leg between Newfoundland and Scotland, four hours were shaved off the usual flight time when using C-124s or C-118s, the run being made in only 6 hours 30 minutes. It was clear that the time savings was tremendous on long distance missions. The international aviation press covered the flight with interest. On an outbound stop in London, the YC-97J was climbing out of Heathrow at 2,500 feet per minute and London ATC asked the pilots to slow the rate of climb as the radar dish was too slow to keep up! The return flight from Frankfurt stopped in Paris, London, the Scotland (Prestwick), Newfoundland (Goose Bay) then Selfridge AFB in Michigan before returning to Kelly AFB. It was the first round-trip trans-Atlantic crossing by an American turboprop aircraft. During the mission to West Germany and back, no engine or prop maintenance was needed and the aircraft's four engines used a mere four quarts of oil for the entire trip. Needless to say, the USAF was very enthusiastic about the aircraft!

In March 1956 the two YC-97Js were put on a scheduled cargo run between Kelly AFB to Ramey AFB in Puerto Rico via Charleston AFB in South Carolina and the return routing stopped over at Brookley AFB in Alabama (now Mobile Downtown Airport). Average flying time between San Antonio and Puerto Rico was 16 hours and despite the stopovers, it was still nine hours faster than what piston-driven USAF transports took to cover the distance. But it didn't stop there- that same month the first YC-97J made the first trans-Pacific crossing by a turboprop aircraft, averaging 360 mph over the 18,000 mile round trip. The longest leg of the route to Tokyo was between Midway Island and Yokota AB outside of Tokyo- on this leg the YC-97J flew at 30,000 feet and averaged 400 mph. 

In preparation for the arrival of the Douglas C-133 Cargomaster, the first group of air crew and mechanics arrived at Kelly AFB from Dover AFB for familiarization training with the T34 engine and its Curtiss propellers. The three-week course had pilots flying an average of 38 hours on the YC-97Js to build turbine experience while the Dover mechanics worked side by side with the Kelly AFB maintenance team to keep the YC-97Js flying. The reliability of the turboprop over the piston engine was now unquestionable and in the summer of 1956, both YC-97Js would fly a total of 46 hours 35 minutes together in a single calendar day as proof of the reliability of the turboprop. The engine overhaul time (TBO) over the course of the test program with the 1700th started out at 150 hours and ended up at 1,000 hours. 

The YC-97J departs San Diego Lindbergh Field.

In addition to its scheduled cargo flights, the YC-97Js were also flown on demonstration flights for interested groups ranging form the US Navy to other defense contractors like Pratt & Whitney and North American Aviation. On a three day demonstration in Connecticut for Pratt & Whitney, the YC-97J made 78 engine starts, 19 takeoffs and landings, 7 air starts and 15 flights without any malfunctions of the engine or propellers. By October, one of the T34 engines became the first American turboprop engine to reach 1,000 flight hours since its last overhaul. It was removed from the YC-97J with 1,001 hours and 20 minutes flight time and in that time, it only needed 44 hours of unscheduled maintenance and used a miserly 392 quarts of oil in that time frame, a fraction of what the regular C-97's piston engines would have used in 1,000 flight hours. The propellers also proved to be extremely reliable and when the first C-133 Cargomasters were delivered to Dover AFB, the engines and propellers were already rated at 1,000 hours TBO, a significant feat in that day. 

The 1700th TS's flight test program with the YC-97Js concluded on 15 November 1956, six weeks ahead of schedule. However, the aircraft were kept operational until 17 January 1957 as they were used in Operation Safe Haven to fly refugees from the 1956 Hungarian Revolution from Europe to new homes in the United States. The first YC-97J, would go on to create more aviation history, though- it was modified to become a Super Guppy transport. Aero Spacelines president Jack Conroy had already flown a piston driven Super Guppy, and aware of the pending retirement of the YC-97Js, acquired one as the turboprop engines made his conversion not only faster, but more efficient. The new turbine Super Guppy used a swing nose instead of a tail break as was the case with the original design and it was put into service with NASA in 1966, its first job transporting the second stage of the Saturn IB rocket from Huntsville, Alabama, where it was built to the Kennedy Space Center in Florida. It was subsequently retired to the Pima Air and Space Museum in Tucson, Arizona. 

Stay tuned for the final installment in this series which will look at the turboprop-powered YC-121F Super Constellation!

Source: Remembering an Unsung Giant: The Douglas C-133 Cargomaster and Its People by Cal Taylor. Firstfleet Publishers, 2005, p29-43. Photos: Smithsonian Institution, SDASM.

The First Steps to a Turboprop Transport, Part One

The YC-131C in flight. Note the 3-bladed propellers.

By the time of the Korean Armistice in 1953, the US Air Force was busy absorbing the lessons of airlift accrued over a less-than-ten-year span from the logistics flights to support World War II to the Berlin Airlift to the strategic airlift partnership forged with the commercial airlines in the Korean War. In pace with advances in aerodynamics and propulsion, the USAF began a four-step process in exploring the possibilities of turboprop propulsion given that pure jet engines of the day were still incredibly fuel-thirsty. The first steps were taken in 1945 with the test program of the Convair XP-81 turboprop fighter that also had an Allison J33 jet engine for additional power. The next steps were the testing of turboprop engines on existing high-speed jet designs that would result in the XF-84H "Thunderscreech and test versions of the Boeing B-47 Stratojet and the McDonnell XF-88 that flew with turboprop engines. The third step was the installation of turboprops on existing transport designs to evaluate their performance on large transports. And the final step was the introduction of production-standard turboprop transports which would result in the Lockheed C-130 Hercules and the Douglas C-133 Cargomaster. 

On 15 June 1954, the headquarters of the Military Air Transport Service (MATS) activated the 1700th Test Squadron (Turboprop) at Kelly AFB, Texas, with the task of developing maintenance procedures and techniques for the employment of turboprop transport aircraft pending the arrival of the C-130 and C-133 into the USAF service. The squadron had three flights with each flight dedicated to a single type for the testing of standard transport aircraft that had been converted to turboprop power. The first of the three flights to be activated would operate the Convair YC-131C. Two aircraft were converted from standard C-131 Samaritan transports (the USAF version of the CV-340 airliner) to use early test versions of the venerable Allison T56 turboprop. The YT56 turboprops replaced the piston engines of the C-131 and drove three-bladed Aeroproducts propellers. As this was the combination planned for the Lockheed C-130A, Allison was, needless to say, keen on being involved in getting flight time for the new engine. Tail numbers 53-7886 and 53-7887 were pulled from USAF service and modified by Convair at their Fort Worth facility at Carswell AFB. After initial flight testing at Edwards AFB, the first YC-131C was flown to Kelly AFB on 20 January 1955 with the second aircraft arriving three days later. 

Ground run of the YT56 engines at Convair Fort Worth.

As the goal of the test program set up by the 1700th TS was to fly the turboprop aircraft assigned to it as much as possible, the YC-131Cs were assigned to a scheduled military passenger service that operated between Kelly AFB in San Antonio and Andrews AFB outside of Washington, DC. The first services began on 14 March 1955 as the first scheduled turboprop passenger services in the United States. Covering a distance of just over 1,200 miles, the YC-131Cs took 4 hours 20 minutes on the first flight, approximately 20 minutes faster than a piston C-131 on the same route. By May of that year a regular flying schedule was established that would have the 1700th TS flying the two YC-131Cs 3,000 flight hours in nine months. As maintenance at destination stations was not expected to be adequate, each scheduled route flown by the YC-131C always returned back to Kelly AFB where the squadron had proper maintenance facilities. By July the Civil Aeronautics Administration (the CAA, the predecessor agency to the FAA) assigned four pilots to the 1700th TS to gain knowledge and experience in scheduled turboprop transport operations. That particular month, the second YC-131C became the first American-built turboprop aircraft to exceed 1,000 flight hours. 

The second YC-131C being handed over the USAF.

In the first six months the YC-131Cs were flown intensively, sometimes over 30 hours per day between the two aircraft. The initial time between overhaul (TBO) on the Allison YT56 engines was set at 100 flight hours at the start of the program but the engine proved to be highly reliable and as the program progressed, the TBO was increased progressively up to 200 flight hours. Though the engines could have safely flown with a longer TBO than 200 hours, Allison engineers were anxious to teardown and study the engines to improve the planned production T56 that would be used on not just the Lockheed C-130 but also on the same company's L-188 Electra airliner. During the nine month test program, 55 engines were changed out and sent back to Allison for analysis. The three-bladed Aeroproducts propellers also had TBO limits, starting at 300 hours and then extended out to 1,000 hours by the end of the test program. With a reliability well in excess of what was possible with piston engines, the two YC-131Cs also became the first USAF turboprops to exceed 1,000 flight hours with one day a record being set with an astounding 46 hours and 20 minutes flown in a 24-hour period, evenly split between the two aircraft. 

On 15 December 1955 the test program with the YC-131C ended, 45 days early thanks to the reliability of the YT56 engine. The USAF gained important data on fuel planning for turboprops, ATC procedures, holding patterns and ground operations that was also shared with the airline industry. In addition, the first squadrons that would be receiving the first C-130A Hercules aircraft at Sewart AFB, Tennessee, Ardmore AFB in Oklahoma, and Eglin AFB in Florida, sent their initial cadre of maintenance personnel to the 1700th TS in San Antonio for familiarization with the T56 engine. Both aircraft were eventually declared surplus and passed on to civilian owners before being scrapped. 

The next blog post will look at the second of the three turboprop conversions operated by the 1700th TS. Stay tuned!

Source: Remembering an Unsung Giant: The Douglas C-133 Cargomaster and Its People by Cal Taylor. Firstfleet Publishers, 2005, p29-43. Photos: Smithsonian Institution, SDASM.