The M115 203 mm howitzer, also known as the M115 8 inch howitzer, was a towed howitzer used by the US Army. Until the 1950s it was designated the 8 inch Howitzer M1. Orignal design started in 1919 but lapsed until resurrected in 1927 as a partner-piece for a new 155 mm gun. It was standardised as 8 inch Howitzer M1 in 1940. The M115/M1 was towed by the M35 Prime Mover gun tractor or a Mack 7⅓ ton 6x6 truck.

The M115 owes some of its origins to the British BL 8 inch Howitzer of the First World War, using the same Welin srcew for the breech. The carriage was the same as used for the US 155mm gun and was also adopted by the British for their 7.2 inch Mark 6 howitzer. The British 8 inch howitzer was produced in both England and under license in the US for the American Expeditionary Forces in Europe during World War I as the 8-inch Howitzer MK.VI. It was in service with the US Army till replaced by the M115. There are no reports of the MK. VI or another marks being used during World War II.

The first photos of the M115 type 8 inch cannon on its redesign carriage appeared in 1931, but development was slowed by the Great Depression.

The M115 saw service in World War II, the Korean War, the Vietnam War, and the Croatia War. In the late 1950s it was adopted in small numbers by several NATO armies to fire the W33 (M454 shell) and later the W79 nuclear artillery shell, a role which ended when the smallest types of tactical nuclear weapons were removed from service and eliminated.

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