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Low-visibility Royal Air Force fin flash on the fin of an Avro Vulcan above the aircraft serial
A fin flash is part of the national markings of the military aircraft of a number of countries.
In addition to the insignia displayed on the wings and fuselage, usually in the form of roundels, an additional marking known as a fin flash may also be displayed on the fin or rudder.
A fin flash often takes the form of vertical, horizontal or slanted stripes in the same colours as the main insignia and may be referred to as rudder stripes if they appear on the rudder instead of the fin, as with the Armée de l'Air of France. Alternatively, a national flag or a roundel may be used.
Images shown below are as they appear on the left side of the aircraft (i.e. with the left side of the fin flash leading) — in cases where there are no asymmetrical details such as coats of arms or text that cannot be reversed, the image may be reversed for the right side, such as with the Royal Air Force fin flash to keep the same side forward much as with a flag. When a national flag is used, the left side of the aircraft is often the back side of the flag as it is normally flown. Exceptions include the German Third Reich's ostensibly "civilian" aircraft in the 1930s, which used the old black-white-red German flag on the right side of the fin and rudder and the Nazi Party flag on the left side.
For some countries, a low visibility variant is also used, to avoid compromising the aircraft's camouflage, and in some cases, to avoid producing a hot spot visible to infrared sensors, such as those used on air-to-air missiles.