Naval ensign is the ensign used by Navy vessels to denote nationality. It can be the same or different from the civil ensign and the state ensign. It's also known as the war ensign. A large version of the naval ensign which is flown on a warship's mast just before going into battle is called a battle ensign. The ensign differs from the jack which is flown from a jackstaff at the bow of a vessel.
Most countries have only one national flag and ensign for all purposes. In other countries, a distinction is made between the land flag and the civil, state and naval ensigns. The elaborate British ensigns, for example, differ from the flag used on land, the Union Flag, and have different versions of plain and defaced Red and Blue ensigns for civilian and state use, besides the naval ensign (White Ensign). Some naval ensign differ in shape from the national flag, such as the Nordic naval ensigns which have tongues.