The Czech hedgehog ( or ) is a static anti-tank obstacle defense made of metal angle beams or I-beams (that is, lengths with an L- or Ɪ-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 attacking infantry, infantry forces are generally much less effective against fortified defensive positions than mechanized units. History World War II 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 a shape similar to later metal versions. However, the concrete hedgehogs proved ineffective during tests as they could be substantially damaged by machine-gun fire. Once they were fragmented, the debris provided more cover for the enemy infantry than did their metal counterparts. Therefore, only the oldest sections of the 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 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 costs" 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 and M5 Stuart tanks. Known as Rhino tanks, these proved very useful for clearing the hedgerows that made up the bocages across Normandy. Cold War Postwar tests conducted by the 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 Panther. As many as 40% of attempts at