A Battle Ensign is the name given to the large war flag flown from warships just before going into battle.

Despite the non-plural use of the name, warships in battle would fly more than one battle ensign. This would ensure that if one of the flags or the halyards that one of the flags would be attached to was shot away, it would not be mistaken by combatants as a sign of surrender (otherwise known as striking the colors).

In the United States Navy, battle ensigns from United States warships, and battle ensigns captured from enemy ships are displayed at the United States Naval Academy at Annapolis, Maryland.

Some countries use their national flag as the Battle Ensign, while others use their naval ensign. Some unique flags made and used as Battle Ensigns include the one flown by United States Naval Forces at the Battle of Lake Erie in the War of 1812.

If warships have to be abandoned, if time permits, one of the battle ensigns would be taken off the ship before it sinks and entrusted to the senior (surviving) ranking officer.

Sometimes, battle ensigns are lost, such as the one flown from USS Arizona during the attack on Pearl Harbor by the Japanese Naval air Forces on December 7, 1941. That flag was badly stained with oil and it was burned as being 'unfit for further use', before anyone thought to save it.

At Other times, battle ensigns are deliberately left with the sinking ship to avoid it's capture. A good example of this was when the Nazi German battleship Bismarck went down with its battle ensign still flying.