High Quality Content by WIKIPEDIA articles! The UGM-96 Trident I, or Trident C4 was an American Submarine-launched ballistic missile, built by Lockheed Martin Space Systems in Sunnyvale, California. First deployed in 1979, the Trident I replaced the Poseidon missile. It was retired in the Early 21st Century, having been replaced by the Trident II. In 1980, the Royal Navy requested Trident I missiles under the Polaris Sales Agreement, however in 1982, this was changed to Trident IIs. It was the first Trident missile to enter service.