Swallowtail (flag)

Swallowtail flag shape

A barn swallow in flight. Note the shape of its tail

In flag terminology, a swallowtail is either

1. a V-shaped cut in a flag that causes the flag to end in two points at the fly; or
2. any flag that has this V-shaped cut.

The name comes from the forked tail that is a common feature of the swallow species of birds.

A swallowtail can also be used to easily deface an existing flag as seen following World War II to both follow international maritime law that dictates a flagged vessel must fly the flag of registration from its stern, but that its use immediately following a war could suggest that the ship is unaware of the surrender or still under orders of the belligerent government.¹

As such, the Allied Control Council in Europe dictated that "every German or ex-German vessel operating under the Allied Control Authority shall at all times wear the Allied Control Authority distinguishing flag which shall consist of International Flag "C" with a triangle cut from the fly.", and Supreme Commander for the Allied Powers in Japan dictated Japanese vessels carry an "D" flag to acknowledge they had accepted Allied occupational authority.²³

Common in the Nordic countries, this swallowtail flag contains a vertical section in the centre of the fly.

Also common in the Nordic countries, the swallowtail flag contains a third tail (the "tongue") between the other two tails.

The triangular swallowtail is the shape of the flag of the American state of Ohio,⁴ as well as of some burgees, private signals and pennants of the International Code of Signals (ICS).

A guidon is the general name given to a small swallowtail flag. Guidons are used to represent military units and are displayed on vehicles attached to a particular unit. In some countries (such as the United States), guidons do not necessarily have a swallow tail.

The military use of the guidon originated from the flags used by cavalry units in Europe. A variant of the guidon, the hussar cut, was used by German cavalry regiments. Instead of a straight V-shaped cut, the swallowtail in a hussar cut flag is curved.