The Type XXI German U-boat, deployed late in World War II, had this nickname.
Milchkuh
Seehund
Elekroboote
Hecht
Elekroboote (electric boat). With a speed of 17.2 knots submerged and a range of 15,500 nautical miles on the surface, this U-boat might have changed the outcome of the Battle of the Atlantic had it been developed prior to 1943. It was more silent underwater and could reload six torpedo tubes in the same amount of time older subs required to load one.