● Submariners are among the most heavily cross-trained personnel in the U.S. military. Each must know how to do everyone else's job in case of an onboard emergency.  A nuclear-reactor operator, for example, also must know how to fire a torpedo, send a radio message, contain a leak or trace an electrical problem.

● Serving onboard submarines is always voluntary.  Candidates are assessed for claustrophobic tendencies and must undergo psychological testing to see if they're suited to living underwater in close quarters.

● Duty onboard Submarines is often referred to as "The Silent Service" because they operate covertly.  Much of their work is classified and intelligence-related.

● Submarines are painted black for the same reason soldiers in Iraq wear desert camouflage.  Underwater, a black submarine blends in with surroundings to help avoid enemy detection.

● Today all United States Navy submarines in the fleets are nuclear-powered, hold more than 100 crewmembers, and can travel more than 800 feet below the sea's surface — the precise depth is classified.