...German submarine U-1206 sank 8 miles off of the coast of Scotland, killing four.
It doesn't sound very noteworthy. A German submarine sank, during war, in enemy waters. Only four people died. Why am I wasting your time with this?
Well, it's reported that the reason the boat sank was because of a toilet.
Early submarines could not be fitted with flushable toilets. One flush while the ship was submerged could completely screw up the water pressure, causing it to sink. By the end of WWII, subs were fitted with new deepwater high-pressure toilets. While they were able to be used while running at depth, the process was extremely complicated and required special technicians to operate them.
Apparently, even with a technician around, things were still able to go wrong. Seawater began to fill the ship after someone flushed. Things got worse when the water level reached some batteries, which caused chlorine gas to fill the ship. The craft was forced to surface in order to get clean air in and to get some of the water out.
That didn't really solve the problem. Remember, they were eight miles from the coast of Scotland. While the boat was getting clean air, it was also getting bombed by Allied aircraft. The damages made the boat unable to dive again, so it had to be abandoned.