page_title: Regulus missile submarines
section_title: Missile submarines
hierarchical_section_title: Regulus missile submarines / History / Missile submarines
caption_attribution_description: USS Grayback (SSG-574), preparing to launch a SSM-N-9 Regulus II missile, circa 1960, place unknown.
context_page_description: The Regulus missile submarines were a group of submarines operated by the United States Navy capable of carrying the Regulus cruise missile. Between 1959 and 1964, a total of five boats were used to undertake the first submarine-based nuclear deterrent patrols by the United States. Regulus submarines were used for this task until 1964, when sufficient ballistic missile submarines carrying the Polaris ballistic missile became available.
context_section_description: Following her conversion, Tunny began a test program, which saw the first Regulus launch from a submarine take place on 15 July 1953. 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. At this point, the boat began being used to develop and trial the operational use of Regulus. At the same time, plans began for the conversion of a second submarine, USS Barbero, for the carriage of the missile. 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. 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.
  At the time that Regulus began development, the US Navy was looking for ways that it could deliver nuclear weapons using its own resources. In the late 1940s, the Navy had planned a class of supercarriers, with the first ordered as USS United States. These ships would be large enough to carry strategic bombers of the size required to carry the nuclear weapons of the time, the specification of which crystallised into the Douglas A-3 Skywarrior. However, the difficulty in designing carrier-based aircraft of the required size to carry nuclear weapons, but capable of operating from the deck of a carrier, which became more of an issue when United States was cancelled, led to the Navy looking at other options for nuclear weapons delivery, and focusing on the concept of submarine launched nuclear missiles, with Regulus a prime candidate. The missile was designed to be able to accommodate the W5 nuclear warhead, before it underwent a redesign to allow carriage of the W27 thermonuclear warhead. The capability of submarines to carry nuclear weapons was seen as significant, as it was possible for submarines to remain undetected on station, with the threat of nuclear retaliation potentially ever present without their presence being known. So, in 1953, the US Navy, with the success of the test programme conducted using Tunny and Barbero, ordered a pair of larger missile submarines capable of carrying twice the number of missiles each. Originally planned as sisters to the attack submarine USS Darter, the two boats, Grayback and Growler, were converted while under construction through the addition of a section containing the missile hangar onto the bow (as opposed to an external installation in the original Regulus boats).
  In addition to their being built to accommodate an increased number of missiles over Tunny and Barbero, the Grayback-class boats were also designed to be able to test what was intended as the second generation cruise missile, which was being developed under the name Regulus II. The rationale for the development of a new missile came from the limitations of the original Regulus - subsonic speed, low range, and the remote control guidance system, which meant that the missile had to stay within range either of its launch vessel, or a platform containing the remote control installation. So, the US Navy ordered the development of a new missile system that eliminated these issues. Regulus II had a range of 1,000 mi (870 nmi; 1,600 km), could fly at Mach 2, and was equipped with its own inertial navigation system that required no input either from the vessel that had launched it, or any other vessels or aircraft en route to its target. The size of the missile meant that the new submarines could only carry a pair of Regulus II missiles each, as opposed to four of the original Regulus airframes. In September 1958, six months after commissioning, Grayback conducted the first successful launch of a Regulus II from a submarine. 
  However, in spite of the success of the Regulus II tes
caption: A Regulus II missile being prepared for launch from Grayback
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