The rapid contest to improve torpedoes

How frequently did torpedo weapons improve in the years leading into and through the Second World War?

Very frequently, with navies continually refining submarine and destroyer torpedoes in a competitive development cycle.

Torpedo development in the prewar and wartime period was nearly continuous. Navies refined submarine and destroyer weapons rather than waiting for a single generational replacement. Work in several maritime theatres fed a sustained technical competition. Date and service context matter because weapons sharing a nominal diameter could still differ after repeated improvements.