Keeping with the submarine theme we have an ingenious invention, the Milchkuh/Milchkühe, or milk cow. These were submarines fitted out to supply other submarines operating against the US east coast in 1942.

Operations against the US east coast were a great success for the U-boats. This was called the Second Happy Time for them. But, more on that later.

The supply subs would bring over food, fuel, and weapon reloads for the attacking submarines. This in turn would lengthen their time on station for the U-boat and increase the chances that they would sink more and more merchant shipping.

The supply submarine concept was also used by the Japanese army at the late stages of the war, a concept no doubt learned from the German’s.