What would follow from Britain fielding a working ballistic-missile submarine force by 1957?
Short answerIt would have to be nuclear-powered, and the United States would likely try to buy or share the British technology.
NotesThe counterfactual gives Britain hydrogen weapons at the same time as the United States and Soviet Union, nuclear submarines by 1955, and a working submarine-launched ballistic missile force by 1957. Nuclear propulsion is treated as necessary for the proposed force. With Britain developing the system before the United States, the Americans would probably try to buy the technology quickly.