“Bubble torpedoes,” that can be launched from a submerged position so they will strike the bottom of a vessel directly above, are reported to have been used recently by German submarines. A vertical tube would permit discharging the torpedo. A special underwater periscope is said to enable the U-boat commander to observe the shadow of a vessel directly above. The primary purpose of such a weapon would be to provide a defense against surface vessels dropping depth bombs, permitting the submarine to make a counterattack from below after it is forced to submerge. The bomb explodes on striking the ship.