The 155 mm gun M1 was a 155 millimeter caliber field gun developed and used by the United States military. Nicknamed "Long Tom", it was produced in M1 and M2 variants, later known as the M59. Developed to replace the Canon de 155mm GPF, the gun was deployed as a heavy field weapon during World War II and the Korean War, and also classed as secondary armament for seacoast defense. The gun could fire a 100 lb (45 kg) shell to a maximum range of 14 mi (23 km), with an estimated accuracy life of 1,500 rounds.

A field gun is a field artillery piece. Originally the term referred to smaller guns that could accompany a field army on the march, that when in combat could be moved about the battlefield in response to changing circumstances, as opposed to guns installed in a fort, or to siege cannons and mortars which are too large to be moved quickly, and would be used only in a prolonged siege.