U-Boats are the names given to German submarines. In World War II, U-1206 was a late war U-Boat fitted with then-new deep water high pressure heads, which enabled them to be used while deep underwater. Flushing these facilities, including toilets, was so complex that special technicians had to be trained to operate them.
On April 14, 1945, U-1206 was cruising at a depth of 200 feet, when a misuse of the new high pressure heads caused water to flood the boat. The water flooded the submarine's batteries under the toilet, causing a leak of chlorine gas, and forcing the crew to surface the boat. Everything would have been okay had they not surfaced near a British patrol. Upon surfacing, the British patrol bombed them, resulting in the death of four men, and capture of forty six more. (source) Image: Source: http://en.wikipedia.org/wiki/German_submarine_U-1206