If World War II magnetic torpedo exploders had worked

How would World War II change if magnetic torpedo exploders had been as reliable as advertised?

Many more ships on all sides would be sunk, especially by submarines, but the scenario also illustrates how unrealistic perfect advertised performance is in actual war.

British attacks on German warships and American submarine attacks in the Pacific would become more lethal if torpedo exploders worked as advertised. The hypothetical is extended to Japanese weapons, so it also increases the danger to Allied ships. The Falklands comparison is a deliberately exaggerated warning about advertised performance: perfect air-defence results are said to imply destroying both sides' available aircraft roughly twice over. Expected weapon performance therefore needs to be distinguished from the results obtained in combat.