The Valiant class were a class of nuclear-powered fleet submarines in service with the Royal Navy from the mid-1960s until 1994. They were the first fully British nuclear fleet submarine; the earlier HMS Dreadnought used an American nuclear reactor. There were only two boats in the class, the first, Valiant commissioned in 1966 three years after Dreadnought, and Warspite the following year. Both were built by Vickers at Barrow-in-Furness.

The seventh HMS Dreadnought was the United Kingdom's first nuclear-powered submarine, built by Vickers Armstrongs at Barrow-in-Furness. Launched by Queen Elizabeth II on Trafalgar Day 1960 and commissioned into service with the Royal Navy in April 1963, she continued in service until 1980. The submarine was powered by a S5W reactor, a design made available as a direct result of the 1958 US–UK Mutual Defence Agreement.