It required only two guidance stations while Matador required three.

Regulus had some advantages over Matador. The Navy concluded that the Navy's Regulus could perform the Navy mission better. Under pressure to reduce defense spending, the United States Department of Defense ordered the Navy to determine if Matador could be adapted for their use. They had nearly identical performances, schedules, and costs. The missiles looked alike and used the same engine. Army-Navy competition complicated both the Matador's and the Regulus' developments. (Later, with the 'Trounce' system (Tactical Radar Omnidirectional Underwater Navigational Control Equipment), one submarine could guide it). It could also be flown remotely by chase aircraft. After launch, Regulus would be guided toward its target by control stations, typically by submarines or surface ships equipped with guidance equipment. The missile resembled an F-84 fighter aircraft, but without a cockpit, and test versions were equipped with landing gear so that they could be recovered and re-used. Regulus was designed to be 30 feet (9.1 m) long, 10 feet (3.0 m) in wingspan, 4 feet (1.2 m) in diameter, and would weigh between 10,000 and 12,000 pounds (4,500 and 5,400 kg). Submarine testing was performed from 1947 to 1953 at the Navy's facility at Naval Air Station Point Mugu, with USS Cusk and USS Carbonero converted as test platforms, initially carrying the missile unprotected, thus unable to submerge until after launch. Regulus development was preceded by Navy experiments with the JB-2 Loon missile, a close derivative of the German V-1 flying bomb, beginning in the last year of World War II.

At its extreme range the missile had to hit within 2.5 nautical miles (4.6 km) of its target 50% of the time. In August 1947, the specifications for the project, now named 'Regulus,' were issued: Carry a 3,000-pound (1,400 kg) warhead, to a range of 500 nautical miles (930 km), at Mach 0.85, with a circular error probable (CEP) of 0.5% of the range. The Navy saw Matador as a threat to its role in guided missiles and, within days, started a Navy development program for a missile that could be launched from a submarine and use the same J33 engine as the Matador. The project stalled for four years, however, until May 1947, when the United States Army Air Forces awarded Martin Aircraft Company a contract for a turbojet powered subsonic missile, the Matador.

In October 1943, Chance Vought Aircraft Company signed a study contract for a 300-mile (480 km) range missile to carry a 4,000-pound (1,800 kg) warhead.

Grayback submarine