Development of the 155mm howitzer M1 began during the late 1930s, when the United States Army determined it needed a new medium field artillery piece to replace the World War One-vintage howitzer M1917.
The 155mm used separate loading ammunition, comprised of four components: a projectile, a separate bagged propellant charge, a fuse, and a primer. The propelling charge contained individual bags of powder, which could be reduced depending on the range of the target. The projectiles weighed 95lb each, with the fuses placed in the base of the projectile after a ring used for shipping was removed. The primers were placed in the breech of the gun for firing. The 155mm howitzer typically fired 80% or more HE (high explosive) shells; however, it could also fire smoke or white phosphorus shells.
In 1962, the designation system for artillery changed, and the 155mm howitzer became known as the M114A1 155mm howitzer. The change in designation didn't detract from its performance in any way during the course of the conflict in Vietnam.