A raid is a specific military intervention aiming at surprising an enemy.
Raids are attacks behind the enemy's lines, usually conducted by a country's special unit of soldiers, specially trained to be mobile on the field.
The collective imaginary, fostered by many historical records, pictures a raid as the intervention carried through by a group of soldiers dressed in camouflage, descending from an airplane and deploying as quickly as a flash.
A raid is synonymous with an assault, which means that the deployment of human forces is unexpected by the enemies and thought in a manner to leave no other options for the targeted men than to surrender. Raids should strike heavily on an opponent's camp to impoverish the warfare capacity of the enemy, and to make retaliation impossible.

In a war, enemies fight face to face in a more or less neutral ground. The battlefield is known from both camps, and soldiers attack or defend themselves in a sort of regularity.
But the raid military tactic, in war-time, plays on surprise. It aims at several purposes: killing or capturing people, ransacking a place, liberating prisoners of war and most frequently confusing people.
The conduct of a raid remains secret until it strikes behind the enemy's lines. Usually, a branch of the army is mobilized to operate such assaults. In this case, a raid is an operation planned by the military authorities and benefits from the legitimacy bestowed to the army. Yet raids may sometimes be caused by small factions of men, like freedom fighters, whose action is not supervised by a form of government.

Commandos and guerrilla fighters may conduct such operations. The body of men both groups form are made of highly trained official or non-official soldiers especially mobile and capable to move in unknown and difficult areas.
History records a high number of raids, among which the 1863's Morgan Raid stands as one of the most spectacular: during the United States' civil war, the confederate cavalry managed to break through 3 northern states. The cavalry both cut the communication lines and captured some of the union's members to prevent its plan of invasion from spreading and being warded-off.