In August 1947, specifications for the Regulus project were issued:[1] The Navy had been experimenting with guided missiles since 1945, using the JB-2 Loon, an American copy of the German V-1.

[3] The first Regulus launch took place in March 1951, using a specially converted test missile fitted with an undercarriage to allow for easy recovery.

[7] At the time, Tunny had not had the missile guidance system installed, which meant she had to operate in conjunction with a ship or submarine capable of controlling the missile once it had been launched; the installation of the guidance equipment was undertaken in early 1954, following which Tunny was capable of independent operations with the Regulus.

Barbero was chosen as she had already undergone a conversion to a cargo-carrying vessel, and thus did not require major modifications to install the missile hangar or equipment.

[8] Barbero was commissioned following her conversion in October 1955 and, following sea trials, entered operational testing alongside Tunny, conducting her first Regulus launch in March 1956.

[14] In 1956, while the test program was still under way, the US Navy instituted a policy of keeping one of its then existing cruise missile submarines in each ocean.

Subsequently, with the ramping up of the nuclear arms race between the United States and the Soviet Union that came following both superpowers successfully launching SLBMs, in 1958 Barbero was moved back to the Pacific to join Tunny, and the newly commissioned Grayback and Growler, to form Submarine Squadron One.

[16][17] This formed a major part of the US Navy's contribution to the nation's overall strategic deterrent, with the policy to continually have a minimum of four Regulus missiles at sea in the Western Pacific at all times.

[4] Nevertheless, between October 1959 and July 1964, when Halibut returned to Hawaii following its final patrol, the Regulus force had maintained at least one submarine constantly on station in the Western Pacific in the strategic deterrent role.

The new boat, renamed as USS George Washington, entered service in December 1959 as part of the Atlantic Fleet, and departed on her first deterrent patrol in November 1960.

In April 1964, having completed a submerged transit from California, USS Daniel Boone arrived at Pearl Harbor for commissioning.

[25] Prior to the cancellation of Regulus II, plans had been in place to build a significant force of cruise missile submarines - fiscal planning estimates intended for three nuclear-powered boats to be funded in 1958, one in 1959, and seven subsequent to this for a total of 12 SSGNs (including Halibut) in addition to the intended 40-45 SSBNs.

[28] However, three months after the successful first launch of a Regulus II missile from the deck of Grayback, it was decided to cancel nuclear cruise missile development to focus solely on Polaris, which was seen as a superior strategic weapon system, while the potential use of Regulus II as a tactical nuclear or conventional weapon was discounted thanks to the US Navy's large fleet of aircraft carriers.

Tunny was originally commissioned in September 1942 as a fleet submarine, and undertook a total of nine wartime patrols in the Pacific during the Second World War, for which she was awarded two Distinguished Unit Citations, before being decommissioned in December 1945.

From 1953 to 1957, the boat was stationed at Port Hueneme as part of the Regulus test program, before transferring to Pearl Harbor to bring the missile into operational service.

The boat's cargo conversion made her a suitable candidate when the Navy elected to commission a second Regulus missile submarine to complement Tunny in February 1955.

Following recommissioning in October, Barbero was employed alongside Tunny in the Regulus test program, being deployed to the Atlantic Fleet in April 1956.

[32] Following the end of her service as part of the nuclear deterrent force, Barbero was decommissioned in June 1964, and sunk as a target off Hawaii in October 1964.

In February 1959 she was deployed to Pearl Harbor to form part of Squadron 1 and undertake strategic deterrent patrols, which continued until 1964, following which Grayback was decommissioned.

Undertaking extensive sea trials throughout 1959, she arrived at Pearl Harbor in September before beginning her first strategic deterrent patrol.

[35] The boat was scheduled to be expended as a target, but in 1988 she was donated to the Intrepid Sea, Air & Space Museum in New York City.

[39] Halibut was decommissioned in June 1976 and struck from the Naval Vessel Register in April 1986, before finally being disposed of through the Ship-Submarine Recycling Program in 1994.

However, starting from USS Providence, the Los Angeles-class submarines were fitted with 12 vertical launch tubes (VLS) for Tomahawk missiles.

[43] The conversion program was integrated with refuelling, and took just over five years to complete all four boats, with work beginning on Ohio in November 2002, and Georgia being released from the shipyard in December 2007.

The insignia was awarded retroactively to the first patrol of the George Washington that was completed in January 1961, but the deterrent missions of the five Regulus boats were not included.

However, in 1997 a change in policy was made that declared the Regulus missions as being equivalent to SSBN patrols, with the insignia ordered to be awarded to all eligible personnel.