A sortie (from the French word meaning exit or from Latin root surgere meaning to "rise up") is a deployment or dispatch of one military unit, be it an aircraft, ship, or troops, from a strongpoint.^[1] The term originated in siege warfare.

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In military aviation, a sortie is a combat mission of an individual aircraft,^[2] starting when the aircraft takes off. For example, one mission involving six aircraft would tally six sorties. The sortie rate is the number of sorties that a given unit can support in a given time.

In siege warfare, the word sortie refers specifically to a sudden issuing of troops against the enemy from a defensive position—that is, an attack launched against the besiegers by the defenders. If the sortie is through a sally port, the verb to sally may be used interchangeably with to sortie.

Purposes of sorties include harassment of enemy troops, destruction of siege weaponry and engineering works,^[3] joining the relief force, etc.

Sir John Thomas Jones, analyzing a number of sieges carried out during the Peninsular War (1807–1814), wrote:^[4]

The events of these sieges show that a bold and vigorous sortie in force might carry destruction through every part of a besieger's approaches, where the guard is injudiciously disposed and ill commanded; but that if due precautions have been observed in forming the approaches and posting the defenders, any sortie from a besieged place must be checked with loss in their advance, when the approaches are still distant; or when the approaches are near, should a sortie succeed in pushing into them by a sudden rush, the assailants must inevitably be driven out again in a moment, with terrible slaughter.