The Poseidon submarine-launched ballistic missile, the follow-on system to the Polaris program, was a two-stage, solid-propellant missile designed to be launched from a submerged fleet ballistic missile (FBM) submarine. It was 2 feet longer than the 32- foot Polaris A3 missile but had a much larger diameter (74 versus 54 inches) and was 30,000 pounds heavier. Despite the increase in size of the Poseidon missile, the growth potential of the FBM submarines allowed Poseidon missiles to fit into the same sixteen missile launch tubes that had earlier carried Polaris missiles. The Poseidon C3 missile was a substantial improvement over Polaris. It provided a greater payload capacity and was capable of delivering multiple warheads, widely spaced, on separate targets over a variety of target footprints. This capability of using multiple independently targetable reentry vehicles (MIRVs) enabled Poseidon to cover a wide range and hold at risk a greater number of targets with nuclear weapons.

The Poseidon C3 missile had a range of 2,500 nautical miles and was the first submarine ballistic missile to be capable of targeting a number of different targets located within the “footprint” of the missile (the area in which individual warheads can be delivered by a single missile). Each 64,000-pound Poseidon C3 could carry up to fourteen Mark 3 reentry bodies. These could be targeted to maximize damage against a single target or targeted against fourteen individual targets. It was also possible to extend the range of the Poseidon by offloading warheads or penetration aids (devices intended to complicate any efforts at missile defense from the payload. Apart from the much-increased size and weight, Poseidon’s main advantage over the Polaris A3 missile was its ability to deliver a warhead to multiple targets. Poseidon C3 also incorporated substantial improvements over Polaris in accuracy and resistance to countermeasures.

The Poseidon missile was deployed initially on thirty-one of the U. S. Navy’s forty-one FBM submarines. The first ten fleet ballistic missile submarines to be built, including five in the George Washington class and five in the Ethan Allen class, were not retrofitted to carry Poseidon. The first launching of a Poseidon missile from a submerged submarine occurred on August 3, 1970, from the USS James Madison (SSBN 627) off the coast of Florida near Cape Canaveral. The Poseidon C3 became operational on March 31, 1971, when the USS James Madison began its initial operational patrol carrying sixteen Poseidon C3 missiles.

In addition to being deployed on Polaris submarines, Poseidon C3 missiles were deployed on submarines, also named Poseidon, that were specially converted to accommodate the larger and heavier missile. In 1970, four SSBN-627 class submarines were converted to carry the Poseidon C3 missile. Although some Polaris submarines were later converted to carry Poseidon, the new Poseidon submarines, at 425 feet long, were much larger than the submarines designed to carry the Polaris missile. They had the same beam width (33 feet) and displaced 8,250 tons (versus 6,700 tons for Polaris). In the 1980s, of the thirty-one Poseidon FBM submarines, twelve were later backfitted to carry the Trident I (C4) missile. The last Poseidon SSBN offloaded its Poseidon C3 missiles and was retired from service in September 1992 (see Polaris SSBNs/SLBMs).

References “Poseidon,” available at http://www.warships1.com/ Weapons/WMUS_Poseidon. htm. Spinardi, Graham, From Polaris to Trident: The Development of U. S. Fleet Ballistic Missile Technology

(New York: Cambridge University Press, 1994). “Submarine Launched Ballistic Missiles,” from United States Nuclear Forces Guide, Federation of American Scientists, available at http://www.fas.org/nuke/ guide/usa/slbm.






Polaris, named after the North Star, was a two-stage ballistic missile powered by solid-fuel rocket motors and controlled by a self-contained inertial guidance system. It was designed to be launched from a submerged submarine. On July 20, 1960, Polaris became the first ballistic missile to be launched from a submarine under water. (In 1942, Germany had successfully test-fired mortar rounds from partially submerged mortar tubes, but no missile had ever been launched from a submerged submarine.) A second A1 Polaris missile was fired three hours later, demonstrating that multiple wartime missile launches were feasible. The Polaris program was the culmination of an intensive four-year program by the Department of the Navy.

There were three versions of the Polaris, designated A1, A2, and A3. Each modification of the missile improved its range, accuracy, target flexibility, and throw weight. Polaris was launched from three classes of fleet ballistic missile nuclear-propelled submarines (SSBNs): the George Washington class, the Ethan Allen class, and the Lafayette class. The first Polaris A2 launch occurred on October 23, 1961, and the first Polaris A3 launch took place on October 26, 1963. Polaris A1 had an initial range of 1,200 nautical miles, and the A2 missile had a range of 1,500 nautical miles. Polaris A1 and A2 carried a single nuclear warhead, and the Polaris A3 carried multiple but not independently targetable warheads. On May 6, 1962, a nuclear-armed Polaris A1 was launched from the USS Ethan Allen while submerged in the Pacific, and its nuclear warhead was detonated over the South Pacific on target. This 1962 launch and nuclear weapon detonation remains the only complete proof test of a U. S. strategic missile ever conducted. The A2 missile became operational in 1962 when it was first deployed on the USS Ethan Allen. The A1 missile was retired in 1965, and the A2 was retired from service in 1974.

The Polaris A3 represented a significantly greater technological advance over Polaris A2, and with an approximately 85 percent new design, it was practically an entirely new missile. With a range of 2,500 nautical miles, it had the ability to reach any land target on the Earth. It also was the only Polaris missile to be equipped with multiple (three) reentry bodies, which were initially intended to serve as a way to penetrate primitive Soviet missile defenses. The first flight test of the A3 was conducted in August 1962, and the A3 became operational in September 1964 when the USS Daniel Webster began its initial operational patrol with sixteen A3s aboard. All Polaris A3 missiles were retired by the U. S. Navy when the last U. S. Polaris SSBN offloaded in February 1982.

The term “Polaris” also is used to describe the submarine on which the Polaris ballistic missiles were deployed. The Polaris submarine was 380 feet long with a 33-foot beam and weighed 6,700 tons. It was designated the 598 class and later the 608 class. There were five submarines in each class. The last Polaris A3 SSBN was reclassified as a nonstrategic submarine and eventually retired from service in 1983.

References Dicerto, Joseph, Missile Base beneath the Sea: The Story of Polaris (New York: St. Martin’s Press, 1967). Spinardi, Graham, From Polaris to Trident: The Development of U. S. Fleet Ballistic Missile Technology (New York: Cambridge University Press, 1994). “Submarine Launched Ballistic Missiles,” from United States Nuclear Forces Guide, Federation of American Scientists, available at http://www.fas.org/nuke/ guide/usa/slbm.


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