A former coworker was in the USN during the post-Korea 50s, and they were trained in how to tie various pieces of their uniforms with air captured inside to use as flotation, in case the ship was going down.
The pants flotation was taught until recently and probably still is.
One thing about crossing water in cold places like Europe during winter is that you do it naked to keep your clothes dry, because of hypothermia, once you cross, you dress.