Abatisses are used in war to keep the approaching enemy under fire for as long as possible.
Abatis, abattis, or abbattis (a French word meaning a heap of material thrown) is a term in field fortification for an obstacle formed of the branches of trees laid in a row, with the tops directed towards the enemy. The trees are usually interlaced or tied with wire. Abatis are used alone or in combination with wire entanglements and other obstacles.
Although used since at least Roman Imperial times, abatis is rarely seen nowadays, having been largely replaced by wire obstacles. However, it may be used as a replacement or supplement when barbed wire is in short supply. A form of giant abatis, using whole trees instead of branches, can be used as an improvised anti-tank obstacle.
An important weakness of abatis, in contrast to barbed wire, is that it can be destroyed by fire. Also, if laced together with rope instead of wire, the rope can be very quickly destroyed by such fires, after which the abatis can be quickly pulled apart by grappling hooks thrown from a safe distance.
An important advantage is that an improvised abatis can be quickly formed in forested areas. This can be done by simply cutting down a row of trees so that they fall with their tops toward the enemy. An alternative is to place explosives so as to blow the trees down.
United States military symbol for an abatis
Though rarely used by modern conventional military units, abatises are still officially maintained in United States Army and Marine Corps training. Current training instructs engineers or other constructors of such obstacles to fell trees, leaving a 1 or 2 meter stump, in such a manner as the trees fall interlocked pointing at a 45 degree angle towards the direction of approach of the enemy. Furthermore, it is recommended that the trees remain connected to the stumps and the length of roadway covered be at least 75 meters. US military maps record an abatis by use of an inverted "V" with a short line extending from it to the right.[1]
Abatis improvised by Japanese troops during World War II
Giant abatis, made from entire trees, can make an effective anti-vehicle obstacle. This formation is often reached by use of explosives--note the splintered stumps.
