By the end of the war a number of light guns, typically 37 mm (a 2 pounder in British measure) were being deployed on short carriages that proved to be considerably better. In addition most forces deployed large high-velocity rifles, typically of .50 cal (12.7 mm) calibre, with enough power to puncture the thin armor of the tanks of the era.
The Soviet Union employed anti-tank dogs, although they weren't very successful.
Anti-tank guns are guns designed to destroy armored vehicles. In order to penetrate the armor of tanks and other armored vehicles they fire high-velocity shells.
Prior to World War II anti-tank guns were relatively small, with anti-tank rifles primarily used for destroying tanks. Few had barrel diameters larger than 50 mm. With the rapid improvement in tank armor and guns anti-tank guns increased in barrel size, firing larger shells at greater velocities. One of the most noteworthy of these weapons was the German 88 mm gun, which was originally developed as an anti-aircraft but found widespread use in destroying tanks. Likewise, by the end of the war all sides were using guns with diameters of 90 mm and up.
World War II also saw the mounting of antitank guns on vehicle chassis, sometimes armored, as a cheap substitute for a full-fledged tank. Some had open turrets, while others did not have rotating turrets at all, meaning that the whole vehicle had to be rotated to aim the gun. Americans called these vehicles tank destroyers. [image] At the start of World War II many of these weapons were still being used operationally, along with a newer generation of light guns that closely resembled their WWI counterparts. In combat both proved entirely useless against the larger and better armored tanks they faced. For instance, the German army had recently introduced a new lightweight 37 mm gun, whose users quickly nicknamed it the "armored door knocker" because all it seemed to do was announce its presence.
All combatants quickly introduced newer and more powerful guns, and the anti-tank rifle had largely disappeared by 1942. The "average" gun by 1943 was 50 mm or larger, the Germans had an excellent 50 mm high velocity design, while the British introduced the "6-pounder" which was also adopted by the US Army as the 57 mm. A year later sizes had grown due to pressure on the Eastern Front, German guns were now 75 mm and the famous 88 mm, while their Soviet counterparts were mounting a variety of 100 mm and 122 mm guns.
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As the guns grew in size they dropped in mobility, leading to the development of the anti-tank vehicle, typically a tank chassis with a much larger gun mounted on top. By the end of the war the concept of the dedicated anti-tank gun was essentially dead, the guns were so large that they were essentially immobile.
The Germans even used HEAT warheads on their now useless 37 mm guns to deliver the warheads at ranges that the rockets couldn't match. However the effectiveness of a HEAT warhead is strongly related to its diameter, so while HEAT was not too effective on "larger" guns like the 75 and 88, on the 37 this was solved by placing an oversized warhead on the outside of the barrel, popped off in a manner similar to a Rifle grenade. This ad-hoc solution was used only in desperation, the recoilless rifle offered the same performance from a much lighter breech-loading gun.
The search for a suitable longer-range delivery system took up much of the immediate post-war era. The US invested in the Recoilless rifle, delivering a widely used 75 mm design, and less-common 90 mm and 106 mm designs (this last one was usually mounted on a jeep rather than hauled across the battlefield by infantrymen). The 106 mm formed the basis of a dedicated anti-tank vehicle, the Ontos tank, which mounted six. The Russians also built recoilless rifles in various calibers intended to be used as antitank weapons, most commonly 73 mm, 82 mm, and 110 mm (only the 73 mm remains in service with the Russian military today, though the other two can be found all over the world, courtesy of Soviet military aid during the Cold War). A massive 120 mm (4.7 inch) Recoilless rifle was built in the UK and issued briefly, but it was found to be too heavy and too massive to be useful, as it had to be deployed mounted on the back of a truck. However most forces, the US included, invested heavily in the development of the wire guided missile as a delivery system, eventually delivering systems in the 1960s that could defeat any known tank at ranges outside that of the guns of the accompanying infantry. The United Kingdom, France, and other NATO countries were among the first to develop such weapons (e.g. the Malkara missile). The United States was one of the last, coming up with the BGM-71 TOW, which was more powerful and easier to use than all the previous missiles, and eventually came to be the most widespread wire guided anti-tank weapon in the West.
Of the world's major armies, primarily the Russians, and some other countries retained the antitank gun in significant quantities, mostly in calibers 100 mm, 115 mm, and, currently in Russia, 125 mm. The 125 mm antitank guns are extremely bulky and massive, and require large tractors to tow them for any significant-distance cross-country, but they're relatively cheap, potentially deadly (particularly now that they've been upgraded with laser rangefinders and Depleted uranium ammunition), though it is not clear what their tactical usefulness is in many types of warfare would actually be. In Desert Storm for example, tanks set up in emplacements were very vulnerable to many weapon systems and could be spotted well in advance. In an environment with more cover they would be harder to spot.
For a time it appeared that the tank was a dead end, a small team of infantry with a few missiles in a well hidden spot could take on a number of the largest and most expensive tanks. In the 1973 Yom Kippur War, Soviet first-generation wire guided missiles being fired by the Egyptian forces inflicted heavy casualties on IDF tank units, a battle that caused a major crisis of confidence for tank designers.
Today the anti-tank role is filled with a variety of weapons, from portable "top attack" missiles, to larger HEAT based missiles for use from jeeps and helicopters, a variety of high velocity Autocannon, and ever-larger heavy tank guns.