"The three Improved-Valiant-class submarines, sometimes known as the Churchill-class,[1] were nuclear powered fleet submarines which served with the Royal Navy from the 1970s until the early 1990s. The lead ship was named for the former British Prime Minister and First Lord of the Admiralty Winston Churchill. The Churchill class was based on the older Valiant class, but featured many internal improvements."
http://en.wikipedia.org/wiki/Churchill_class_submarine