Swallowtail (flag)

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.

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.