1. The Boeing C-17A Globemaster III set new standards for military airlift in the time following its maiden flight in 1991. It did this by combining strategic and tactical capabilities in a heavy-weight, wide-body aircraft with short takeoff and landing (STOL) performance. However, the U.S. Air Force's C-17 had a torturous decade-long struggle from concept to first flight. This was largely because ofpolitical and monetary decisions, in addition to the technological problems. This gestation, and that of other aircraft that followed, might have been more difficult had it been necessary to demonstrate the technologies and methods for achieving STOL capability in a large transport aircraft before embarking on development ofa productionrepresentative aircraft. This demonstration and validation step was eliminated on the basis ofthe AirForce's earlierAdvanced Medium STOLTransport (AMST) program that yielded the Boeing YC-14 and McDonnell Douglas YC-JS test aircraft. In a remarkably short time and with an extraordinarily small budget, the AMST effort produced engineering test data and operational insight into the advantages and disadvantages of two very different approaches to achieving STOLperformance in wide-body military transport aircraft. However, even these aircraft built upon the knowledge and experience gleaned from otherflight technology programs worldwide. This important and fascinating chapter of aviation history is related herein.
2. The Advanced Medium STOL Transport (AMST) was a concel 1ed effort by the U.S. Air Force to develop an aircraft of the type described by the name. The result grew out of a 1968 operational requirement issued by the Air Force's Tactical Air Command (TAC) for a tactical transport supporting rapid battlefield air mobility. It would do this by delivering outsized Army combat vehicles and other cargo to forward-deployed troops. Outsized essentially meant wider than the cargo compartments ofthe Lockheed C-130 Hercules and C-141 Starlifter, yet still able to fit within the C-S Galaxy. The "Herk" and Starlifter cabin widths were designed to accept a standard 9-ftwide (2.7 m) cargo pallet that spanned these compartments: 10.3 ft (3.3 m) width and 9.2 ft (2.8 111) height for the C-J30 and 10.3 ft (3.3 m) width and 9.1 ft (2.8 m) height for the C-141. The ongoing Southeast Asia experience appeared to substantiate the need to deliver greater quantities of cargo, including vehicles, to short, unpaved fields just behind the forward edge of the battle area (FEBA). The aircraft was also to possess cruise airspeed commensurate with turbine-engine propulsion for high productivity and range sufficient for self deployment across oceanic distances.
3. At the time TAC stated its requirement the looming introduction of the large-capacity Lockheed C-S strategic airlifter meant that massive quantities of weapons and supplies would be delivered to major airports from the continental United States. However. there was inadequate tactical airlift to distribute the cargo to forward-deployed combat elements in a timely manner. The standard U.S. Army vehicles had grown beyond the capabilities of the Hercules. which first entered service in 1956 and was still being procured. The ahility of a large transpOl 1 aircraft to operate from unpaved runways would greatly increase the Army's ability to rapidly supply its troops deployed in Europe in reaction to the far more numerous forces of the Warsaw Pact. It was assumed that major airfields would be bombed in the first days of a war, requiring aircraft to operate on either the shol 1 portions of runways and taxiways that remained intact or from roads and unpaved surfaces (Fig. I). One stated TAC goal was to airlift an Army brigade, with all its vehicles, to the FEBAwithin 24 hours. Just the ability to deliveratank or self-propelled howitzer to a forward airstrip would be a tremendous combat advantage for the U.S. Army, bypassing possibly days oftravel on congested roads. The Army heartily endorsed the AMST concept.
4. The AMST requirements would undoubtedly drive the design of the largest STOL aircraft attempted to that time, with the application of advanced technologies appearing essential. Plans were that a successful program would likely yield an aircraft in the mid-1980s to replace the C-130 Hercules, Fairchild C-123 Provider (Fig. 2), and de Havilland Canada C-7 Caribou (Fig. 3). The C-123 and C-7 were about as old as the C-130, with the Providerenteringservice in 1955 and the Caribou in 1962,although both designs dated farther back than their service entry dates. (The Caribou initially entered service with the U.S. Army as the CV-2 before all were turned over to the Air Force in 1967 as part of the I January 1967 agreement between the two services on the division of responsibilities for fixed-wing aircraft operations.) These two types had suffered considerable wear and approximately 50% attrition during the Vietnam War and their many years of service. The C-123s and C-7s had done yeoman duty in Southeast Asia while the C-J30 had begun tactical operations fairly late in the conflict. However, the interior dimensions and payload-weight capacity ofthese aircraft were such that most loads flown into the theater by Military Airlift Command (MAC) C-141s, C-133s, and C-124s frequently had to be extensively broken down and repackaged for loading on the tactical transports. The TAC airplanes also flew comparatively slowly and with limited range such that deployment to the theater of operations took too much time and their productivity was low-although the C-130 did much better in this