vehicles to tow them into place, and were difficult to conceal, dig in, withdraw, or reposition. By 1945, large anti-tank guns had become almost impractical in their role, and their size and weight were considered liabilities. They were also expensive to produce and although they were capable of defeating the most formidable of opponents, most tank units still consisted of less heavily armoured models that remained vulnerable to less expensive and more practical guns, as well. Many heavy anti-tank guns were issued, at least initially, on the divisional level, but gradually made their way to individual infantry battalions. Meanwhile, the effect of very compact hollow charge warheads was being noted, and a number of countries began producing man-portable anti-tank weapons using this ammunition. The development of man-portable, shoulder-fired, anti-tank rocket launchers began in 1941; most could be reloaded, but a few, such as the German Panzerfaust, were fired from disposable tubes. Unlike anti-tank guns, their light weight made them easily portable by individual infantrymen on the battlefield, and they offered similar degrees of firepower whilst being quicker and cheaper to produce. Towed anti-tank guns disappeared from most Western countries, such as the United States, after World War II, to be replaced by shoulder-fired rocket launchers, recoilless rifles, and eventually, guided anti-tank missiles. Postwar period At the end of the war, German engineers had proposed a new, large-caliber anti-tank gun that used less propellant than a rocket or recoilless weapon, yet fired similar compact hollow-charge shells. German forces subsequently fielded the 8 cm PAW 600, which was an extremely lightweight, low-pressure weapon still able to fire the same ammunition types as higher-velocity anti-tank guns. In the 1950s, this idea was revived by a Belgian firm, Mecar, which subsequently improved on the concept and developed a low-pressure, smoothbore, 90-mm anti-tank gun. Because of its low recoil forces and light construction, the gun was particularly useful for being mounted on armored cars or small gun carriages. Its design inspired the lightly rifled French DEFA D921 anti-tank gun, which fired fin-stabilized shells and was available on a towed carriage or as a vehicle mount. It was later mated to the AML-90 and EBR series of French armored cars. The Soviet Union also adopted a similar design around the same time, the 100-mm T-12 anti-tank gun, which was smoothbore and fired fin-stabilized shells. Switzerland developed a postwar 90-mm anti-tank gun of its own, the Pak