At a moment's notice, the entire crew can be called to quarters to respond to casualties or to man battle stations to launch torpedoes or missiles. Ventilation fans and running equipment provide a constant background white noise that the sailors learn to tune out. Experience provides a submariner with a sensitivity to subtle changes in the background noise that alert him to changes in the ship's operating parameters or to potential problems. This sensitivity, this unconscious condition of alertness is on all the time, even during sleep. Consequently, a deep, restful sleep is never possible.
Submariners recognize that they are working in a hostile environment.
Sharing their long metal tube is a nuclear reactor, a steam-driven engine room, a torpedo room filled with explosive conventional warheads, and missile tubes that potentially contain nuclear warheads. In addition, miles and miles of electrical cabling connect hundreds of switchboards. More miles of piping carry cooling water to various components, high pressure hydraulic oil to operate control surfaces, masts, and periscopes, and high pressure air to launch torpedoes or blow water from the ballast tanks in order to surface. The submarine must distill fresh water from seawater to provide pure water for the steam plant and potable water for cooking and hygiene. Even the mundane functions must be provided.