On April 14, 1945, German captain Karl-Adolf Schlitt took a fancy U-1206 submarine into combat patrol for the first time. The sub had a new high-tech toilet that, according to the War Is Boring blog, "directed human waste through a series of chambers to a pressurized airlock" and "then blasted it into the sea with compressed air, sort of like a poop torpedo." After using the new-fangled crapper Schlitt apparently turned the wrong valve, allowing a backflow of waste and seawater into the sub, and it only got worse from there:
The unpleasant liquid filled the toilet compartment and began to stream down onto the submarine's giant internal batteries — located directly beneath the bathroom — which reacted chemically and began producing chlorine gas.
As the poisonous gas filled the submarine, Schlitt frantically ordered the boat to the surface. The crew blew the ballast tanks and fired their torpedoes in an effort to improve the flooded vessel's buoyancy.
Somehow, it got worse when the submarine reached the surface. "At this point in time British planes and patrols discovered us," Schlitt wrote in his official account.
After taking damage from an air attack, the only option was to scuttle the sub and order the sailors overboard.