When a group of soldiers is sent on a specific mission, it's called a sortie. A fighter pilot's sortie might involve a mission to drop a bomb on a target and return to base.
When a fighting unit is deployed, heading out on a military mission, you can describe it as a sortie. A sortie might involve troops moving across a field toward their enemy, or a tank advancing on a city held by rebels. Sometimes a sortie involves a sudden surge or attack. In French, the word sortie literally means "a going out," from a Latin root, surgere, or "rise up."