Regulus: The US Navy's First Operational Nuclear Missile

Regulus missile on an aircraft carrier deck.

Following the defeat of Germany in May 1945, the US Navy began experimentation with the German V-1 "buzz bomb" as a submarine-launched weapon called the JB-2 Loon. Both the Navy as well as the Army drew up plans to use the JB-2 during the planned invasion of the Japanese Home Islands, but the war in the Pacific ended in August of that year before the plans could be put into place for use of the Loon. This didn't put a stop to development work, though- in March 1946, Secretary of the Navy James Forrestal approved plans to convert two submarines to operate the Loon on an experimental basis. While the Loon was never planned in the postwar period to be an operational missile, it was planned to give the submarine force experience in operating cruise missiles. In 1947 the Navy began development of several supersonic land-attack cruise missiles- one was the Mach 2 Rigel and the other was the Mach 3.5 Triton, both powered by ramjets. At the time, ballistic missile technology was at a point where they weren't practical nor compact enough to be fired from submarines, so the Navy was hitching its submarine nuclear deterrent on the cruise missile. The level of technology required for the Rigel and Triton were far above what was state of the art for the late 1940s, so while development work continued and technology matured, an interim cruise missile for the sub force was needed and this task was given to Vought Aircraft who then developed the Regulus missile- originally planned to carry a 4,000 lb conventional warhead, in 1949 Vought was directed to use a nuclear warhead on the Regulus, making the first US Navy missile to carry a nuclear warhead. 

The Regulus featured folding wings and a tail fin to allow it to be carried aboard a submarine. Powered by an Allison J33 engine (also used on the Lockheed F-80 and T-33 Shooting Star), Regulus was a subsonic missile with an approximately 500 nautical mile range. It was boosted from the missile by two solid rocket boosters that fell away once the J33 engine took over propelling the missile. The missile guidance was by radio command- the system was called "Trounce" and it directed the missiles nearly all the way to the target. Not only were submarines and ships capable of guiding Regulus using Trounce, but the Navy also had specialized Regulus guidance squadrons equipped with the North American FJ Fury that could be embarked aboard fleet carriers as needed. The first Regulus flight took place on 29 March 1951- this early Regulus missile had its own landing gear to take off and land under its own power and was controlled from another aircraft. Test launches were made from surface ships the following year. 

Firing a Regulus from the USS Tunny.

Two diesel-electric submarines were the first to be converted to carry and fire the Regulus. The USS Tunny (SSG 282, the "G" for missile) and the USS Barbero (SSG 317) were fitted with a rather cumbersome hangar aft of the conning tower which itself was modified to carry the Trounce guidance equipment. Converted at the Mare Island shipyards near San Francisco, the Tunny was recommissioned in March 1953 and the Barbero returned to the fleet in October 1955. The first submarine launch of the Regulus took place on the USS Tunny on 15 July 1953. On both ships, the Regulus missile hangar would hold two missiles- to fire the Regulus, the submarine had to surface and the missile had to be manually rolled out of the hangar and manually unfolded to prepare it for launch. 

While the submarine force got ready for the Regulus, the Navy went ahead and deployed it from surface ships (several cruisers and aircraft carriers deployed with the Regulus) with the 50 kiloton Mk 5 warhead starting on May 1954. The first overseas deployment of the Regulus actually took place with surface ships- in 1955 the cruiser USS Los Angeles (three missiles) and the aircraft carrier USS Hancock (four missiles) deployed to the Western Pacific to cover Soviet targets in the Far East. It wasn't until 1958 that the Regulus went to sea aboard a submarine. Joining the USS Tunny and USS Barbero were two purpose-built diesel electric subs that were modifications of an existing design- the USS Grayback (SSG 574) and the USS Growler (SSG 577) were completed in 1958- the Grayback was built at Mare Island and the Growler was built at the Portsmouth shipyards in New Hampshire. There were plans initially to have Regulus capability on the first nuclear submarine, the USS Nautilus, but it was felt to minimize risk, the Nautilus was completed as a non-cruise missile submarine. However, funds were made available for a nuclear-powered Regulus submarine, and in 1960 the USS Halibut (SSGN 587) was commissioned, giving the US Navy five Regulus-armed boats. 

The first submarine nuclear deterrent patrol took place during the 1958 Lebanon crisis when the USS Tunny was ordered to patrol in the North Pacific to make up for the usual aircraft carrier that would have been present to hold Soviet targets in the Far East "at risk". This was more than two years before the first ballistic missile submarine, the USS George Washington, went to see with the Polaris SLBM. The USS Barbero was assigned to the Atlantic fleet and carried out deterrent patrols there from April 1956 to late 1958 before the Navy consolidated its Regulus subs with the Pacific Fleet. From September 1959 to July 1964, the Navy had at least one submarine on deterrent patrol in the North Pacific- the diesel electric boats would refuel at either Adak, Alaska, or Midway Island, before going out on the patrol. The sole nuclear-powered Regulus boat, the USS Halibut, didn't need the refueling stops. During that period, forty-one Regulus patrols were conducted, sometimes two of the subs were on patrol at once. The Regulus missiles during this period were armed with two megaton W27 warhead which replaced the earlier Mk 5 warhead.

Regulus launch from the USS Halibut.

The successor to the Regulus was to have been the supersonic Regulus II with twice the range and a heavier warhead. The development got as far as having a Regulus II fired from the USS Grayback in September 1958, but three months after the sub launch the Regulus II program was canceled as the decision had been made to accelerate and enlarge the Polaris missile program which was shaping up to be a much more practical system than cruise missiles. The Regulus missiles were retired as the Polaris come on line, the last Regulus deterrent patrol taking place in July 1964 which was five months before the Polaris missile patrols commenced in the North Pacific. Both the Barbero and Tunny were scrapped, but the Growler would become a museum boat in New York City at the Intrepid Sea-Air-Space Museum (it has a Regulus missile displayed in launch configuration). The USS Grayback become a special forces transport and served in this role until 1984. The USS Halibut had an impressive second career as an intelligence platform to carry out clandestine ocean operations. It served in this role until 1976. 

The Regulus ended up being an interim placeholder for the US Navy until the arrival of the ground-breaking Polaris missile. For almost five years, the Regulus subs patrolling the North Pacific were the only submarine nuclear deterrent. In fact, the USS Halibut was the second nuclear sub to be built to operate missile armament- the honor of the first actually goes to the USS George Washington with its Polaris missiles. It was launched five days before the USS Halibut in 1960, but it wasn't until late 1964 that it went on an operational deterrent patrol with Polaris.

Source: Cold War Submarines- The Design and Construction of US and Soviet Submarines by Norman Polmar and KJ Moore. Potomac Books, 2004, p86-93. Photos: US Navy Historical Center, Wikipedia.