This two-stage solid-propellant Fleet Ballistic Missile is launched underwater from nuclear-powered submarines. The Poseidon is launched by compressed air, with first-stage ignition just after the missile is clear of the hull. Poseidon carried the Mk-3 Multiple Independently targeted Reentry Vehicles (MIRV)—thermonuclear weapons which enable a single missile to cover a number of targets.

The first successful test flight of Poseidon was from Cape Canaveral on August 16, 1968, and the first submarine launch was from the U.S.S. James Madison on August 3, 1970.

The Poseidon C-3 is from the U.S. Navy and Lockheed Aircraft Corporation.