An ensign is the national flag flown on a vessel to indicate nationality. The ensign is the largest flag, generally flown at the stern (rear) of the ship while in port. The naval ensign (also known as war ensign), used on warships, may be different from the civil ensign (merchant ships) or the yacht ensign (recreational boats). Large versions of naval ensigns called battle ensigns are used when a warship goes into battle. The ensign differs from the jack, which is flown from a jackstaff at the bow of a vessel.
In its widest sense, an ensign is just a flag or other standard. 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. In Arab armies, "ensign" is a unit title equivalent to a Western brigade, and as a rank is equivalent to a divisional commander.
Ensigns, such as the ancient Roman ensigns in the Arch of Constantine, are not always flags.
In nautical use, the ensign is flown on a ship or boat to indicate its organizational membership. 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 European and Commonwealth countries.
Many countries do not distinguish among these uses, and employ only one national flag and ensign in all cases; in the United States, for example, all ships of the seagoing services of the United States Government with the exception of the United States Coast Guard fly the national flag as their ensign, although the ships of some agencies also fly an agency flag as a "distinguishing mark." Other countries (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 vessel is a warship, a merchant ship, a ship under contract to carry mail, 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 Grand Union Flag 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.
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.
The Blue Ensign as currently used for British government vessels
The Red Ensign as currently used for British civilian vessels
The Civil Air Ensign as currently used by UK civil aviation establishments
Australian national Flag and State Ensign
New Zealand Red Ensign
Indian Navy Ensign
Belgian Navy Ensign
Egyptian Navy Ensign
Civil and Naval Ensign of France
Naval ensign of Italy
Myanmar navy ensign
North Korean navy ensign
Ensign of the Royal Norwegian Navy
Ensign of the Royal Danish Navy
Polish Navy ensign
Naval Ensign of the Royal Saudi Navy
Spanish yacht ensign
Naval ensign of Sri Lanka
Naval ensign of Thailand
Ukrainian Navy ensign
United States Coast Guard ensign
Royal Dutch Navy ensign
Naval ensign of Vietnam