The Czech hedgehog (Czech: rozsocháč or ježek) is a static anti-tank obstacle defense made of metal angle beams or I-beams (that is, lengths with an L- or H-shaped cross section). The hedgehog is very effective in keeping light- to medium tanks and vehicles from penetrating a line of defense; it maintains its function even when tipped over by a nearby explosion. Although Czech hedgehogs may provide some scant cover for infantry, infantry forces are generally much less effective against fortified defensive positions than mechanized units.
The Czech hedgehog's name refers to its origin in Czechoslovakia. The hedgehogs were originally used on the Czech–German border by the Czechoslovak border fortifications – a massive but never-completed fortification system that was turned over to Germany in 1938 after the occupation of the Sudetenland as a consequence of the Munich Agreement.
The first hedgehogs were built of reinforced concrete with the shape similar to later metal version. But the concrete hedgehogs proved ineffective during the tests as they could be substantially damaged by machine-gun fire. Moreover, even when turned into debris it provided more cover for the enemy infantry than the metal counterpart. Therefore, only the oldest sections of Czechoslovak defensive line built in 1935–1936 were equipped with concrete hedgehogs and usually only in the second line.
The Czech hedgehog was widely used during World War II by the Soviet Union in anti-tank defense. They were produced from any sturdy piece of metal and sometimes even wood, including railroad ties. Czech hedgehogs were especially effective in urban combat, where a single hedgehog could block an entire street. Czech hedgehogs thus became a symbol of "defense at all cost" in the Soviet Union; hence, the memorial to Moscow defenders, built alongside the M-10 highway in 1966, is composed of three giant Czech hedgehogs.
Czech hedgehogs were part of the German defenses of the Atlantic Wall. During the invasion of Normandy the Allies cut up sizable numbers of intact and wrecked hedgehogs, and welded them to the front of their M4 Sherman tanks and M5 Stuart tanks. Known as Rhino tanks, they proved very useful for clearing the hedgerows that made up the bocages across Normandy.
The postwar tests conducted by Czechoslovak army proved the low efficiency of the metal hedgehogs against heavy armored vehicles such as the Soviet ISU-152 and T-54 or German PzKpfw V Panther. As many as 40% attempts for breakthrough were successful for which the army developed new anti-tank obstacles for the purpose of the border fortifications activated during the Cold War. But the metal hedgehog was still used as the quick road-block against wheeled vehicles.
A Czech hedgehog made to specifications could be constructed from any material capable of withstanding at least 60 tonnes-force (600 kN), while being at most 1.4 metres (4 ft 7 in) high. Such parameters, however were hard to achieve in makeshift hedgehogs, thereby reducing their usefulness.
The hedgehog is not generally anchored to prevent movement, as it can be effective even if rolled by a large explosion; instead, its effectiveness lies in its dimensions, combined with the fact that a vehicle attempting to drive over it will likely become stuck (and possibly damaged) through rolling on top of the lower bar and lifting its treads (or wheels) off the ground. 
Industrially manufactured Czech hedgehogs were made of three pieces of metal angle (L 140/140/13 mm, length 1.8 metres (5 ft 11 in), weight 198 kilograms (437 lb); later versions: length 2.1 metres (6 ft 11 in), weight 240 kilograms (530 lb)) joined by gusset plates, rivets and bolts (or, later in the war, welded together) into a characteristic spatial three-armed cross with each bar at right angles to the other two. (This pattern forms the axes of an octahedron.) Two arms of the hedgehog were connected in the factory, while the third arm was connected on-site by M20 bolts. The arms were equipped with square "feet" to prevent sinking into the ground, as well as notches for attaching barbed wire.
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