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with the current shortage of pilots and maintenance personnel. It took a major effort of his entire battalion to maintain an availability rate of 58 percent.

The story of airmobility is essentially one of men and machines. If the Huey helicopter became the cornerstone of airmobility, then the Chinook must be considered one of the principal building blocks.

Late in 1956 the Department of the Army announced plans to replace the H-37 helicopter, which was powered by piston-driven engines, with a new, turbine-powered aircraft. A design competition was held and, in September 1958, a joint Army-Air Force source selection board recommended that the Army procure the Boeing Vertol medium transport helicopter. However, the necessary funds to proceed with full-scale development were not available and the Army vacillated in its design requirements. There were those in the Army who felt that this new helicopter should be a light tactical transport aimed at the mission of the old H-21's and H-34's and, consequently, sized for approximately fifteen troops. Another faction believed that the new transport should be much larger to serve an artillery prime mover and have minimum interior dimensions compatible with the Pershing Missile system. This "sizing" problem was a critical decision.

The first Vertol prototype, called the YHC-1A, was tested by the Army to derive engineering and operational data. Three aircraft were built with a maximum troop capacity of twenty. This model eventually became Vertol's commercial 107 and the Marine Sea Knight. However, the YHC-1A was considered by most of the Army users to be too heavy for the assault role and too light for the transport role. The decision was made to procure a heavier transport helicopter and at the same time upgrade the Huey to a tactical troop transport. This decision was to determine the pattern of airmobile operations for the next decade. As a consequence, the Army concept of air assault operations differed from the Marines because, among many reasons, the very nature of the equipment demanded different methods of employment.

The "sizing" of the Chinook was directly related to the growth of the Huey and the Army's tacticians' insistence that initial air assaults be built around the squad. There was a critical stage in the Huey program when the technicians insisted that we should not go beyond the UH-1B model with Bell; that there should be