For most of World War 2, Germany had enjoyed having the largest and most advanced fleet of submarines at its disposal. The ...

While the Type XXI subs sank no ships, their potential terrified Allied navies, prompting intensified anti-submarine efforts.

The result was the Kriegsmarine's almost complete reliance on U-boats during the rest of the Battle of the Atlantic. In the end, the U-boats were the Kriegsmarine's most effective weapons.

Then in March 1943, the Kriegsmarine revised the Enigma encryption system it used to communicate with U-Boats, which the Allies had hacked. In March 1943, U-Boats sank 120 ships for ten losses.

German Kriegsmarine U-boats and submarines from the Imperial Japanese Navy were always on the prowl in the waters of the Atlantic and Pacific Oceans, ready to sink troop transports and accomplish ...