1) German U-boats were a key part of Germany's naval strategy in World War 2, operating worldwide with the goal of disrupting Allied shipping.
2) The "Wolfpack" tactic, developed by Admiral Donitz, involved coordinating groups of U-boats to attack convoys together for greater effectiveness.
3) Key U-boat operations included "Operation Drumbeat" against U.S. shipping from bases in occupied France in 1942, though Allied codebreaking and convoy escorts led to declining successes by 1943.