HMS Dreadnought shows how a fixed date changes the submarine order of battle. Britain's first nuclear submarine was still in service in 1980 and was due to decommission during the year. A major war would probably halt that retirement and keep the boat available. On that basis, every Royal Navy SSN class built to that point could potentially serve, alongside Oberon-class diesel-electric submarines and other retained boats.
Notable Point · 1:38:53-1:39:30
HMS Dreadnought was still available in 1980
A war early in 1980 could retain HMS Dreadnought and place every Royal Navy nuclear-submarine generation then built, plus conventional boats, into the mobilisation pool.