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 typical example. Ambush can be described geometrically as: Linear, when a number of firing units are equally distant from the linear kill zone. L-shaped, when a short leg of firing units are placed to enfilade (fire the length of) the sides of the linear kill zone. V-shaped, when the firing units are distant from the kill zone at the end where the enemy enters, so the firing units lay down bands of intersecting and interlocking fire. This ambush is normally triggered only when the enemy is well into the kill zone. The intersecting bands of fire prevent any attempt of moving out of the kill zone. Viet Cong ambush techniques Ambush criteria: The terrain for the ambush had to meet strict criteria: provide concealment to prevent detection from the ground or air enable ambush force to deploy, encircle and divide the enemy allow for heavy weapons emplacements to provide sustained fire enable the ambush force to set up observation posts for early detection of the enemy permit the secret movement of troops to the ambush position and the dispersal of troops during withdrawal One important feature of the ambush was that the target units should 'pile up' after being attacked, thus preventing them any easy means of withdrawal from the kill zone and hindering their use of heavy weapons and supporting fire. Terrain was usually selected which would facilitate this and slow down the enemy. Any terrain around the ambush site which was not favorable to the ambushing force, or which offered some protection to the target, was heavily mined and booby trapped or pre-registered for mortars. Ambush units: The NVA/VC ambush formations consisted of: lead-blocking element main-assault element rear-blocking element observation posts command post Other elements might also be included if the situation demanded, such as a sniper screen along a nearby avenue of approach to delay enemy reinforcements. Command posts: When deploying into an ambush site, the NVA first occupied several observation posts, placed to detect the enemy as early as possible and to report on the formation it was using, its strength and firepower, as well as to provide early warning to the unit commander. Usually