thumb|French-designed DEFA D921/GT-2 90 mm towed anti-tank gun as mounted on a [[Ordnance QF 17-pounder|QF 17-pounder carriage]]
An anti-tank gun is a form of artillery designed to destroy tanks and other armored fighting vehicles, normally from a static defensive position. The development of specialized anti-tank munitions and anti-tank guns was prompted by the appearance of tanks during World War I. To destroy hostile tanks, artillerymen often used field guns depressed to fire directly at their targets, but this practice expended too much valuable ammunition and was of increasingly limited effectiveness as tank armor became thicker. To penetrate armor, they fired specialized ammunition from longer barrels to achieve a higher muzzle velocity than field guns. Most anti-tank guns were developed in the 1930s as improvements in tanks were noted, and nearly every major arms manufacturer produced one type or another. A few Soviet designs saw combat well into the 1980s and 1990s.
History
World War I and Interwar period
thumb|right|Two British officers with a captured [[Mauser 1918 T-Gewehr]]
The first specialized anti-tank weaponry consisted of anti-tank rifles. These emerged from the mixed results of deploying field artillery against tanks during World War I, and the need to produce a more economical weapon to destroy them. The 3.7 cm Pak 36 which first appeared in 1928 was probably the first purpose-built anti-tank gun.
Introducing improved ammunition and increasing muzzle velocity initially helped compensate for their mediocre performance, but small-caliber anti-tank guns clearly would soon be overtaken by yet more heavily armored tanks. This helped earn the Pak 36 the moniker of Panzeranklopfgerät ("tank door knocker") because its crew revealed their presence and wasted their shells without damaging the T-34's armor.
Postwar period
thumb|250px|Postwar Soviet MT-12 100-mm anti-tank gun
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 a recoilless weapon, yet fired compact, hollow-charge shells similar to those used by the latter. 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. The last country known to have produced a dedicated anti-tank gun was the People's Republic of China in 1988. The Chinese gun was known as the Norinco Type 86 and was probably manufactured as a replacement for the aging Soviet-sourced T-12.
Anti-tank guns continued to be used in many conflicts around the world, such as the Six-Day War and the South African Border War.
Self-propelled anti-tank guns
thumb|250px|A British [[Archer (tank destroyer)|Archer tank destroyer, based on the hull of a Valentine tank.]]
Although still being drawn by horses or towed by trucks, towed anti-tank guns were initially much lighter and more portable than field guns, making them well-suited to infantry maneuvers. As their size and caliber increased, though, the guns likewise became increasingly heavy and cumbersome, restricting their role to static defense. Consequently, during World War II, both sides were compelled to make anti-tank guns self-propelled, greatly increasing their mobility. and were used in the Battle of France The trend continued with older tanks and captured vehicles, which were available in large numbers for conversions to self-propelled guns when they were replaced by heavier and better-armed (and armored) tanks. The introduction of tank destroyers also put an end to the traditional tactic of suppressing anti-tank gun batteries with heavy artillery bombardments, as their crews were now well-protected under armor.