page_title: SSM-N-9 Regulus II
section_title: Design and development
hierarchical_section_title: SSM-N-9 Regulus II / Design and development
caption_attribution_description: Launch of U.S. Navy Vought SSM-N-9 Regulus II cruise missile.
context_page_description: The SSM-N-9 Regulus II cruise missile is a supersonic guided missile armed with a nuclear warhead, intended for launching from surface ships and submarines of the U.S. Navy.
context_section_description: The major drawback of the original Regulus was the use of radio-command guidance, which required a constant radio link with the launch ship / submarine that was relatively easy to interfere with. The earlier missile also suffered from restricted range which required the launch ship to launch the missile close to the target and remain exposed until the missile hit the target. To alleviate these drawbacks, the Regulus II was designed with an inertial navigation system, which required no further input from the launch ship / boat after launch, and a greater range through improved aerodynamics, larger fuel capacity, and a lower specific fuel consumption from its jet engine.
  Prototype missiles were built, designated  XRSSM-N-9 Regulus II, with retractable landing gear, to allow multiple launches, and Wright J65-W-6 engines and Aerojet General booster, which restricted them to subsonic flight. The first flight of the XRSSM-N-9 took place in May 1956. Beginning in 1958, testing was carried out with the  XRSSM-N-9a, equipped with the General Electric J79-GE-3 turbojet and a Rocketdyne solid-fueled rocket booster to allow the entire flight envelope to be explored. Evaluation and training missiles with retractable undercarriage were produced as the YTSSM-N-9a and TSSM-N-9a respectively.
  After land-based testing, trials including test missile firings were carried out on board the USS King County (LST-857), which had been modified with the replica of a submarine missile hangar and launching system.
  The SSM-N-9 Regulus II missile was intended to be launched from the deck of an SSG (guided missile submarine), and the missile most likely would have been deployed on the two Grayback-class submarines and the USS Halibut (SSGN-587), which were designed for the missile, and possibly eventually on four heavy cruisers that had deployed with Regulus I and 23 other submarines potentially available for conversion. Carrying two Regulus II missiles in a hangar integral with the hull (more on surface ships), submarines and ships equipped with the Regulus II would have been equipped with the SINS (Ship's Inertial Navigation System), allowing the control systems of the missiles to be aligned accurately before launching.
  Forty-eight test-flights of Regulus II prototypes were carried out, 30 of which were successful, 14 partially successful and only four failures. A production contract was signed in January 1958 and the only submarine launch was carried out from USS Grayback in September 1958.
  Due to the high cost of the missiles (approx one million dollars each), budgetary pressure, and the emergence of the SLBM, the Regulus missile program was terminated on 19 November 1958. Support for the program was finally withdrawn on 18 December 1958, when Secretary of the Navy Thomas S. Gates cancelled the project. At the time of the cancelation, Vought had completed 20 missiles with 27 more on the production line.
caption: Regulus II test launch in 1957. The swept-forward Ferri-style intake can be seen.
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