The colloquial description of the large square red flag which used to be hoisted at the mastheads of British men-of-war to indicate that they were about to go into battle. Other nations also hoisted distinctive flags at the mastheads of their ships during battle. The main purpose for these flags was to serve as an aid to distinguishing friend from foe in the smoke of action. More recently, warships of all nations going into battle hoisted their national ensign, for this purpose known as a battle ensign, at the masthead or other prominent position.
Subjects: Maritime History.