[173] In early 1958, when the Soviet Union and the United States had each launched two satellites, it was obvious, from comparing their weights, that the Soviets were using a much more powerful launch vehicle. This led to great concern in the United States about the apparent lag in vehicle capability-a concern welcomed by space enthusiasts for it meant more support. This concern, however, was not entirely justified when all the technological gains associated with the development of intercontinental and intermediate range ballistic missiles are considered. Indeed, modifications of these vehicles provided the base for the U.S. "stable" of launch vehicles in the early years of the space program. One ICBM, the Atlas, established the feasibility of lightweight, pressure-stabilized tanks, a technology important for favorable consideration of lowdensity liquid hydrogen. For all these reasons, a review of the development of Vanguard, the first U.S. vehicle developed solely as a launch vehicle, and military ballistic missiles during the 1950s is helpful in understanding launch vehicle planning during 1958 and 1959.