The 37 mm Gun M3 was the first dedicated anti-tank gun fielded by United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 forces. Introduced in 1940, it became the standard anti-tank gun of the U.S. infantry

Infantry

Infantrymen are soldiers who are specifically trained for the role of fighting on foot to engage the enemy face to face and have historically borne the brunt of the casualties of combat in wars. As the oldest branch of combat arms, they are the backbone of armies...

 with its size enabling it to be pulled by a jeep

Willys MB

The Willys MB US Army Jeep and the Ford GPW, were manufactured from 1941 to 1945. These small four-wheel drive utility vehicles are considered the iconic World War II Jeep, and inspired many similar light utility vehicles. Over the years, the World War II Jeep later evolved into the "CJ" civilian...

. However, the continuing improvement of German

Nazi Germany

Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

 tank

Tank

A tank is a tracked, armoured fighting vehicle designed for front-line combat which combines operational mobility, tactical offensive, and defensive capabilities...

s quickly rendered the 37 mm ineffective, and by 1943 it was being gradually replaced in the European

European Theater of Operations

The European Theater of Operations, United States Army was a United States Army formation which directed U.S. Army operations in parts of Europe from 1942 to 1945. It referred to Army Ground Forces, United States Army Air Forces, and Army Service Forces operations north of Italy and the...

 and Mediterranean

Mediterranean Theater of Operations

The Mediterranean Theater of Operations, United States Army was originally called North African Theater of Operations and is an American term for the conflict that took place between the Allies and Axis Powers in North Africa and Italy during World War II...

 theaters by the more powerful British-developed 57 mm Gun M1

Ordnance QF 6 pounder

The Ordnance Quick-Firing 6-pounder 7 cwt, or just 6 pounder, was a British 57 mm gun, their primary anti-tank gun during the middle of World War II, as well as the main armament for a number of armoured fighting vehicles...

.