Operation Regenbogen (U-boat)
In the Operation Rainbow is a command of Grand Admiral Karl Doenitz of 30 April 1945 to sink all ships and submarines that are not suitable for fishing or mine sweeping, so you do not need to pass the enemy.
This command invoked at the end of World War II to the directive issued by Adolf Hitler that "no soldier of the Wehrmacht, or another, under German command combat unit ever capitulate to the enemy " should.
On May 4, Doenitz took command back due to the terms of surrender and ordered to hand over all ships. However, many captains ignored the second command and sank their boats in or outside the ports. 216 U- boats ( another source: 232) were blown up or sunk here by opening the valves.