"The pre-war designs of the "S", "U" and "T" class submarines were the basis of the designs for all British submarines completed in time to take part in Britain's World War II submarine operations. Many changes in the features of these submarines were, however required as the war progressed, and this resulted in the designs being completely reviewed on several occasions. The advances in offensive and defensive qualities brought about by war experience were embodied as quickly as design considerations and the limited available building capacity permitted."