By 1945, the Battle of the Atlantic was won by the Allies. However the Germans clung to the hope that wonder weapons and superior technology could somehow turn the tide. U-1206 was a brand new Type VIIC boat that could travel faster and stay submerged longer than U-boats before it.
Part of the reason U-1206 could stay submerged for long times was the toilet system. Unlike Allied submarines where human waste went into a holding tank, waste on German U-boats was flushed directly into the sea. The lack of a holding tank allowed more space for other critical necessities, like fuel and batteries. This also meant that the waste couldn’t be flushed out while submerged too deeply, an unfortunate olfactory situation for a submarine if it was submerged for too long. The Type VIIC boats fixed this problem, not with a holding tank, but a complicated high pressure valve system that permitted a crew member to flush while deeply submerged. The valve system was so complicated that “Toilet Specialists” were needed to operate it.
On 14 April 1945, the captain of U-1206 was taking his daily constitutional while submerged off Scotland. He didn’t want to bother the toilet specialist to flush, so he broke out the manual to do it himself. In the process, he stuffed up the toilet. Swallowing his pride, but not too much, he called the boat’s engineer to fix the problem instead of the junior ranking toilet specialist. While trying to unplug the toilet, the boat’s engineer opened the wrong valve and seawater flooded into the boat. The water eventually reached the boat’s batteries and the chemical reaction caused a cloud of chlorine gas. The crew brought the boat to the surface so they could open the hatches to air the gas out. While on the surface, U-1206 was promptly sunk by the RAF.