Ballistic Missiles

Long-range ballistic missiles entered American military service during the late 1950s. They are called ballistic because, like the shell from a gun, they receive a brief but powerful initial impetus (from a rocket motor), then follow an unpowered ballistic trajectory after launching.

Polaris was the first U.S. Navy ballistic missile system—a nuclear-powered submarine with 16 guided missiles, each armed with a nuclear warhead many times more powerful than those used in World War II. The first model of the missile, Polaris A-1, went to sea in late 1960. Polaris A-2 became operational in 1962, A-3 in 1964. The Poseidon missile succeeded Polaris beginning in 1972, followed by Trident I in 1979, and Trident II in 1990. Each step brought major advances in warheads and accuracy.

Models of Submarine-launched Ballistic Missiles (SLBMs)
Scale models show the relative size of the six types of U.S. SLBM: Polaris A-1 (1960), Polaris A-2 (1962), Polaris A-3 (1964), Poseidon C-3 (1972), Trident I C-4 (1979), and Trident II D-5 (1990). All six missiles used solid fuel in multiple stages: two stages for Polaris and Poseidon, three for Trident.

All versions of Polaris had a diameter of 4.5 feet (1.3 m), but they grew longer—28 to 31 to 32 feet (8.5 to 9.5 to 9.8 m)—and heavier—14 to 16 to 18 tons. They also increased in range—1,200 to 1,500 to 2,500 nautical miles (2,200 to 2,700 to 4,600 km)—and accuracy. Polaris A-3 missiles carried multiple warheads, or MRV (for multiple reentry vehicle, the protective covering that keeps the warhead from burning up during atmospheric reentry).

Poseidon, although longer and considerably heavier than Polaris A-3, had the same range. It also had MIRV (multiple independently targetable reentry vehicle) and improved accuracy. Trident I marked another step forward in performance with greater range (4,000 nautical miles [7,400 km]), improved guidance, and still better accuracy. Trident II is the longest ranged and most accurate of all U.S. SLBMs to date. It is also by far the biggest—44 feet (13 m) long, just under 7 feet (2 m) in diameter, and weighing 65 tons. It can only be carried in the Ohio-class submarines specifically designed for the purpose. Courtesy Lockheed Martin Corporation, Bethesda, Maryland

Weapons Shipping Hatch
Through this small hatch from the USS Trepang (SSN-674), sailors eased the skid-mounted 3,000-pound (1,360-kg) torpedo down into the submarine.

Inside this mockup of an upper level missile compartment on USS James K. Polk (SSBN-645) can be seen the Sitka spruce nose cone fairing from a Trident I missile. It shields the warheads as the missile accelerates upward through the atmosphere. The aerospike, which extends after launch, balances the airflow during acceleration. Both fairing and aerospike are jettisoned after serving their purposes. Above the tube is suspended the blue watertight closure that protected the missile from seawater before launching. Courtesy Strategic Systems Programs, U.S. Navy

Back to: Homepage / Submarine Weapons