A sortie (from the French word meaning exit) is a deployment or dispatch of one military unit, be it an aircraft, ship, or troops, from a strongpoint. The sortie, whether by one or more aircraft or vessels, usually has a specific mission. The sortie rate is the number of sorties that a given unit can support in a given time.
In siege warfare, a sortie, or sudden issuing of troops against the enemy from a defensive position, can be launched against the besiegers by the defenders. If the sortie is through a sally port, either to sortie or to sally can be used.
In military aviation, a sortie is a combat mission of an individual aircraft, starting when the aircraft takes off and ending on its return. For example, one mission involving six aircraft would tally six sorties.
In naval terms it can also be used to describe a full-scale evacuation of a fleet of ships, their accompanying aircraft and submarines from a posting in advance to avoid a natural disaster such as a hurricane.
In spaceflight, especially for NASA's Constellation Program, the term sortie has been used for a flight of the Orion spacecraft beyond the confluence of low-Earth orbit, such as a flight to the Moon or to the Sun-Earth L2 Lagrange Point. This term was not used by NASA for the nine Apollo flights that flew by, orbited, or landed on the Moon between 1968 and 1972.