An ensign is, in its widest sense, a flag or other standard. In particular, ensign has commonly been used to mean the flag or other standard of a ship or military unit.
Today, the term is most commonly used in reference to ships, on which the ensign is the largest flag, generally flown at the stern (rear) of the ship. Naval ensigns today do indicate the ship's (nominal) nationality, but may be a specifically naval ensign rather than the normal national flag.
The European military rank of ensign, once responsible for bearing a unit's standard (whether national or regimental) derives from it (in the cavalry the equivalent rank was cornet, named after a type of flag). In contrast, the Arab rank of ensign, liwa, derives from the command of a unit or units with an ensign, not the carrier of such a unit's ensign, and is a general officer.
Large versions of naval ensigns called battle ensigns are used when a warship goes into battle.
In nautical use, the ensign is flown on a ship or boat to indicate its appartenance. While this includes its nationality, it may well indicate more information (e.g. civilian, naval, or police vessel) rather than being the national flag itself. This is particularly common for commonwealth and European countries.
- A civil ensign (usage symbol ) is worn by merchant and pleasure vessels. In some countries the yacht ensign, used on recreational boats or ships instead of merchant vessels, differs from the civil ensign.
- A state ensign or government ensign (usage symbol ) is worn by government vessels, such as coast guard ships.
- A naval ensign (usage symbol ) is used by a country's navy.
Many countries do not distinguish between these uses, and employ only one national flag and ensign in all cases. Others (like the United Kingdom, Ukraine, Italy, Russia, South Africa, Australia, New Zealand, and Japan) use different ensigns. Such ensigns are strictly regulated and indicate if the boat is a warship, a merchant vessel or a yacht, for example.
Several Commonwealth countries' national flags had their origin in the ensigns of their original colonising power, the United Kingdom. Most notable of these national flags are those of Australia, New Zealand, and several smaller island nations. It is also very likely that the original design from which the flag of the United States developed was strongly influenced by the British Red Ensign or the flag of the (British controlled) East India Company.
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With the creation of independent air forces and the growth in civil aviation in the first half of the 20th century, a range of distinguishing flags and ensigns were adopted. These may be divided into air force ensigns (often light blue in colour, such as the Royal Air Force Ensign) and civil air ensigns.
- Znamierowski. "Types of flags". The world encyclopedia of flags. p. 31.
- Znamierowski. "Naval ensigns and flags". The world encyclopedia of flags. p. 88.
- Snell, Melissa. "Pimbley's Dictionary of Heraldry".
- Znamierowski. "Air force flags". The world encyclopedia of flags. p. 85.