In the navy, "hot bunking" means sharing beds. This is particularly necessary in attack submarines, where space is at a premium. In a typical submarine, up to 40% of the crew (not the officers, no doubt) will have to "hot bunk", usually by having three sailors share two beds by working and sleeping in shifts.
"Hot bunking" is often used as an excuse to keep women and homosexuals out of active duty on submarines. Fear of cooties, I guess.