Rules of Prize Warfare defines a set of rules for taking vessels during war that were originally laid down in the days of sailing ships. Some of the rules state that: passenger ships may not be sunk; crews of merchant ships must be placed in safety before their ships may be sunk (life boats are not considered a place of safety unless close to land); only warships may be sunk without warning.

All sides signed treaties subscribing to Rules of Prize Warfare before World War I and they were in effect during World War II but all sides completely ignored them in both wars. The treaties are still in effect today.