submarines had been commissioned, and the START I treaty had gone into effect, so the 31 older Poseidon- and Trident I-armed SSBNs were disarmed, withdrawing Poseidon from service. Operators United States Navy Gallery See also List of missiles References Cold War weapons of the United States Nuclear weapons of the United States Cold War submarine-launched ballistic missiles of the United States Lockheed Corporation UGM-073 Military equipment introduced in the 1970s