With the demise of Rigel, the Regulus successor became another Chance Vought product designated Regulus II. In March 1954, the Navy planned to have Regulus II operational by 1957 and Triton operational in 1965. Vought began design of the supersonic winged missile in April 1952, receiving a development contract in June 1953. Thirty-six months later, the first Regulus II flew when a 115,000-pound- thrust booster launched the canard-configured missile. Regulus II could carry its 2,920-pound warhead 570 nm at Mach 2, and over 1,150 nm at reduced speeds. One suggestion in 1957 was to fit wing tanks on the missile to extend its range.
The Navy successfully tested a recoverable Regulus II test vehicle in 30 of 48 tests, achieved partial success in 14, and failed in only 4. The government signed a production contract in January 1958. That September the Navy fired a Regulus II from the submarine Grayback, the only such launching. The Navy scheduled one other snorkel submarine to be equipped with Regulus II, along with four cruisers, and planned in 1956 to eventually put Regulus on 23 submarines.
Despite early promise, the Regulus submarines were severely disadvantaged by the requirement to prepare and fire their missiles on the surface and then to stay at periscope depth to exercise command guidance. These shortcomings were overcome when more compact nuclear warheads and larger solid-fuel rocket motors became available, and with submarine nuclear propulsion, motivated the concept of submarine-launched ballistic missiles (SLBMs) as a nuclear deterrent.
The missile's cost (one million dollars each), budget pressures, and the greater attractiveness of alternative nuclear delivery systems doomed Regulus. The Regulus missile program was terminated to free funds for the Polaris project. On 19 November 1958, the Office of the Secretary of Defense withdrew its support from the program; and on 18 December 1958, Secretary of the Navy Gates canceled the project. At that point, Chance Vought had completed 20 of the missiles with 27 others still on the production line. SSGNs on order were recast as SSN-593 class attack submarines, though existing Regulus submarines continued operations.
USS Halibut (SSGN-587) was the first nuclear powered submarine specifically designed to carry and launch missiles. Commissioned in January 1960, she could carry four Regulus II missiles in a hangar integral with the hull. She is also the first submarine to carry the Ships Inertial Navigation System (SINS). In 1964 USS Halibut made the last Regulus patrol. With Polaris on line, Regulus submarines were phased out.