Hot racking (also known as hot bunking or hot bedding) is the sanctioned practice within military organizations of assigning more than one crew member to a bed or "rack" to reduce berthing (sleeping) space. The practice dates back at least to the sixteenth century, and today is particularly applied aboard submarines, where maximization of space is especially important. Generally, the lowest ranking members of the crew are required to hot rack. Hot racking is sometimes utilized in jails and prisons to deal with overcrowding.
Also, 'hot racking' has come to refer to people in the navy who wear their uniform to bed without either showering or changing, (i.e. hot rack).[citation needed]
Depending upon the watch system, two, or even three people may end up sharing the same bunk. The term comes from the military slang use of the term "rack" for a bed or bunk. With more than one crew member assigned to a rack, it is possible that a crew member returning from a duty shift will lie down on a rack immediately after it is vacated by another crew member about to start a shift. The rack is therefore said to be "hot." That is, warm from the vacating crew member.
This practice is almost forgotten in the modern United Stars Navy, as ships are built much bigger. However in the early years of United Earth and during the early years of the Union, especially Destroyer crews where space was used for weapons and systems and every cubic meter of ship space was expensive to build and maintan.