The Taranto torpedoes carried a contact pistol for direct hits and a magnetic pistol intended to fire beneath a hull. The magnetic settings may not all have worked perfectly in the harbour. The Royal Navy nevertheless had an unusual advantage because its ships and bases gathered knowledge of magnetic conditions around the world. Reliable magnetic fuzing depended on understanding how the Earth's field varies by location, making global operating experience part of weapons engineering.
Notable Point · 3:28:49-3:29:41
Why magnetic pistols demanded global data
The duplex torpedo combined contact and magnetic firing, while worldwide naval operations supplied data needed to tune the magnetic mechanism.