 This alert was in response to the crisis posed by the Soviet attack on Hungary which suppressed the Hungarian Revolution of 1956.Between 1957 and 1961 the United States followed an ambitious and well-funded program to develop a nuclear-powered cruise missile, Supersonic Low Altitude Missile (SLAM).It was designed to fly below the enemy's radar at speeds above Mach 3 and carry hydrogen bombs that it would drop along its path over enemy territory.