In February 1953, the US Navy began a program to replace the Regulus-I missile. This one had just been put into production, but the missile did not have the proper perfomances. Although the program was called Regulus-II, the new missile was a completely new design with more range, supersonic speed and inertial guidance system. The missile could be launched within minutes of the submarine surfacing. The test missiles were equipped with a landing gear and parachute, and in December 1959, the first Mach 2 flight was achieved. The deployment of Regulus-II was projected on several cruisers, 2 conventional submarines and 4 nuclear submarines, but in 1958 due to cuts in the defense budget, the program was canceled in favor of Polaris SLBM missile. The manufactured training missiles were used by the US Navy and the USAF as supersonic target drones for the Bomarc air defense missile program, totaling about 50 flights as air targets.
REGULUS II gallery and more info