The 6 pounder anti-tank gun was developed by Woolwich Arsenal beginning around 1938 due to the limitations of the 2 pounder anti-tank gun then in service. The 57 mm bore was developed as there were guns that size already used by the Royal Navy and not much new equipment was needed to build them. The design was set by 1940, but with the war on it didn't enter production till late 1941. The gun was successful in its role and continued in British service until the '60's.
The U.S. started production of the gun in 1941, then known as the 57mm Anti-Tank Gun Model M1, as a Lend Lease gun and was distributed as such, including to the Free French Forces. It was adopted by the U.S. when it was found that its favorite gun in the anti-tank role, the 37mm gun, was ineffective. Some bigger bore sizes and carriages were developed, but in the end the gun was built as the British designed it. The U.S. built over 15,000 guns by the end of WW2.
The 57mm gun acquitted itself well during WW2, especially for the British in North Africa. It easily penetrated tanks at the beginning of the war, but had more trouble at extended ranges when the new Tiger I and Panther tanks were introduced. The U.S. used it in North Africa and Italy, but was less useful in Normandy. There was a shortage of armor piercing ammunition for the U.S., and the gun couldn't take on contemporary German armor except for the sides or rear. Also since it had to be towed it was less useful than self propelled guns. It was dropped from U.S. service at the end of the war.
The gun pictured guards Confidence Cemetery in Georgetown, Ohio. Georgetown is the county seat of Brown County, and is also the boyhood home of Ulysses S. Grant. The gun was built by International Harvester after 1943 and sits on the M2 carriage. It still has its armored side plates, which traditionally went unused during the war. As in most guns relegated to cemetery duty, its breech is welded up and parts are missing, and could use a new coat of paint. Oddly enough, the tires look to be in great shape, unusual for a graveyard gun.
Guns of this type were mounted on several British tanks and armored cars, including the Churchill tank, and the U.S. mounted it in the M3 half track. The Royal Navy mounted it in gunboats, which also had a quick loading mechanism, enabling the gun to fire 6 rounds in as many seconds. The 57mm gun was adopted by Israel after the war and was used during the Suez Crisis.