The German Rettungsboje or Udet Buoy was a unique rescue device to help pilots who crashed in the English channel survive the cold water until rescue during the Battle of Britain in 1940. Well equipped with survival gear and supplies, it helped air crews stay dry and provide first aid until boats or air rescue could bring them back to base.

The British later built a similar boat called the ASR10.
One survives today at the Scottish Maritime Museum.
https://www.scottishmaritimemuseum.org