Fox is a brevity code used by NATO pilots to signal the simulated or actual release of an air-to-air munition or other combat function. Army aviation elements may use a different nomenclature, as the nature of helicopter-fired weapons is almost always air-to-surface. "Fox" is short for "foxtrot", the NATO phonetic designation for the letter "F", which is short for "fire". A fighter pilot announcing that a weapon has been fired is intended to help avoid friendly fire, alerting other pilots to avoid maneuvering into the path of the munition.

There are three variations of the Fox brevity word in use, with a number added to the end of Fox to describe the primary type of sensors the launched munition possesses (if applicable). This includes auto cannons and collisions.

Fox one

Indicates launch of a semi-active radar homing missile (such as the AIM-7 Sparrow).^[1]:

Fox two

Indicates launch of an infrared homing missile (such as the AIM-9 Sidewinder).^[1]

Fox three

Indicates launch of an active radar homing missile (such as the AIM-120 AMRAAM or AIM-54 Phoenix).^[1]

Prior to the advent of active radar homing missiles the code 'Fox three' referred to the use of guns or cannon, such as the M61 Vulcan which is used in various military aircraft. The difference can be noted in various war films, notably in the 1986 film Top Gun, where the term is used in various dogfight scenes.