UGM-27 Polaris

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The Polaris missile was a submarine-launched, nuclear-tipped ballistic missile (SLBM) built during the Cold War by the United States Navy. It was designed to be used as part of the US Navy's contribution to the United States' nuclear deterrant, replacing the Regulus cruise missile.

Lockheed developed the solid-fuel Fleet Ballistic Missile (FBM), which first flew from Cape Canaveral on January 7, 1960.

The Polaris's first version, the A-1, weighed 28,800 lb (13.1 t), stood 28.5 ft (8.7 m) tall, had a diameter of 54 in (1.4 m), and had a range of 1,000 nautical miles (1,850 km). A test launch from a submarine on July 20, 1960, was the first underwater rocket launch. The USS George Washington was the first fleet ballistic missile submarine (SSBN in US naval terminology) and carried 16 missiles. Forty more SSBNs were launched by 1966.

Work on its nuclear warhead began in 1957 at the facility now called the Lawrence Livermore National Laboratory by a team headed by Harold Brown. The Navy accepted delivery of the first 16 warheads in July 1960, and first launched one from a submarine on November 15.

On May 6, 1962, a Polaris missile with a live W47 warhead was tested in Operation Dominic I, the only U.S. test of a live nuclear missile.

Later versions (the A-2, A-3, and B-3) were larger, weighed more, and had longer ranges. The range increase was most important: The A-2 could fly 1,500 nautical miles (2,300 km), the A-3 2,500 nautical miles (4,600 km), and the B-3 2,000 nautical miles (3,700 km). The A-3 featured multiple independently-targeted reentry vehicles (MIRVs) and the B-3 was to have penetration aids to counter Soviet Anti-Ballistic Missile defenses. The B-3 evolved into the C-3 Poseidon missile.

Polaris missiles had two stages, both steered by thrust vectoring. An inertial navigation system could guide the missile to about a 900-meter (3000 feet) circular error probability. This made them unsuitable for use against hardened targets, which means they were mostly useful for retaliation.

The missile began to be replaced by Poseidon beginning in 1972. In the 1980s both were replaced by the Trident I.