Page:A Concise History of the U.S. Air Force.djvu/59

 off at a moment's notice; another was dispersed to satellite bases around the world, complicating Soviet targeting; while a smaller was actually airborne. The DOD's ultimate solution was the Triad, maintaining three primary nuclear forces, each with special advantages. The first element of the Triad was the manned bomber, important for its load-carrying and ability to be recalled once launched. ICBMs formed the second component. They were important for their speed, size, and, eventually, accuracy. Early ICBMs, the Atlas and Titan I, burned cryogenic liquid propellant and required extended launch preparations which rendered them vulnerable to a first strike. In the 1960s later model Titans IIs employed storable propellants and, joined by the solid-propellant Minuteman, were placed in protective silos and capable of near-instantaneous launch. Submarine-launched ballistic missiles (SLBMs), including the Polaris, Poseidon, and Trident, comprised the third component of the Triad. Able to roam the world's oceans, missile submarines represented the most survivable of the three legs. Although the sub-launched solid-propellant ballistic missiles at first lacked range and accuracy, technology soon removed these drawbacks. The second problem created by a countervalue strategy and massive retaliation had to do with the control and integration of diverse weapon systems into a single American war plan. In 1959 President Eisenhower ordered that a single integrated operational plan (SIOP) be adopted, which required coordination by the Army, Navy, and Air Force. The need for SIOP became apparent when in the late 1950s an investigation revealed that the military services had targeted Moscow with fewer than 170 nuclear bombs and warheads in case of all-out war. The third problem had to do with intelligence. America's first steps into space, the "ultimate high ground," were associated with intelligence, surprise attack prevention, and nuclear war planning. The Air Force also sought to exploit space for communications, navigation, and weather forecasting. Chuck Yeager and the XS-1 rocket aircraft, the first to break the sound barrier, began pushing back the aerospace frontier in 1947, as did other experimental aircraft that flew over 301,000 acres of desert testing ground in California at Edwards Air Force Base's Air Force Flight Test Center. The X-15 rocket airplane flew nearly seven times the speed of sound and seventy miles high in the mid-1960s―records that still stand for winged aircraft. In 1957 the Air Force began the Dyna-Soar program, later designated the X-20, to build a manned space boost glider/aerospace plane. Dyna-Soar was cancelled in 1963 in favor of a Manned Orbital Laboratory, itself scrapped in 1969 because automated satellites could