Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. UGM-133 Trident II, or Trident D5 is a Submarine-launched ballistic missile, built by Lockheed Martin Space Systems in Sunnyvale, California, and deployed with the Royal Navy and US Navy. It was first deployed in 1990, and is still in service. Trident II was developed in response to the development of a large number of heavy, increasingly accurate, MIRVed ICBMs, such as the R-36, by the Soviet Union. These missiles seriously threatened the survival of Minuteman III missiles in their silos. If the Soviet Union could knock out the majority of these missiles and strategic bombers when on the ground, it would have left the United States with no retaliatory capabilities.