An ambush is a long established military tactic in which an ambushing force uses concealment to attack an enemy that passes its position. Ambushers strike from concealed positions such as among dense underbrush or behind hilltops. The tactic is generally used to gather intelligence or to establish control over an area.
Ambushes are complex multi-phase operations and are therefore usually planned in some detail. First a suitable killing zone is identified. This is the place where the ambush will be laid. It is generally a place where enemy units are expected to pass, and which gives reasonable cover for the deployment, execution, and extraction phases of the ambush patrol. A path along a wooded valley floor would be a classic, if rather obvious, example.
To be successful an ambush patrol must deploy into the area covertly, ideally under the cover of darkness. The patrol will establish secure and covert positions overlooking the killing zone. Usually, two or more cut off groups will be sent out a short distance from the main ambushing group into similarly covert positions. Their job is twofold; firstly to give the ambush commander early-warning of approaching enemy (usually by radio), and secondly, when the ambush is initiated, to prevent any enemy from escaping. Another group will cover the rear of the ambush position and this give all round defence to the ambush patrol.
Care must be taken by the ambush commander to ensure that fire from any weapon cannot inadvertently hit any other friendly unit.
Having set the ambush, the next phase is to wait. This could be for a few hours or a few days depending on the tactical and supply situation. It is obviously much harder for an ambush patrol to remain covert and alert if sentry rostas, shelter, sleeping, sanitary arrangements, food and water, have to be considered. Ambush patrols will almost always have to be self-sufficient as re-supply would not be possible without compromising their covert position.
The arrival of an enemy in the area should be signalled by one of the cut-off units. This may be done by radio or by some other signal, but must be done silently. The ambush commander will have given a clear instruction for initiating the ambush. This might be a burst from an automatic weapon, use of an explosive device (such as a claymore mine), or possibly a simple whistle blast. When the ambush commander judges that the ambush will be most effective he gives the signal.
After the firefight has been won, the now compromised ambush patrol will need to leave the area as soon as practical. Before this is done it is a common practice to clear the killing zone by checking bodies for intelligence, taking prisoners, and treating any enemy wounded. If communication orders permit, a brief contact report may be sent. This done, the ambush patrol will leave the area by a pre-determined route.
In civilian situations, the term ambush also means hiding where an intended victim is likely to come and committing some violence against him if he does. The legal term for it is "lying in wait," and in most criminal codes it is an aggravating factor, raising the seriousness of the crime and, therefore, increasing the penalty for it, because it proves premeditation.