The M110 self-propelled howitzer first entered service with the U.S. Army in 1963 and was used in the Vietnam War. Later versions were used in Operation Desert Shield and Operation Desert Storm by T Battery, 5th Battalion, 11th Marines, and the British Army. In 1977, the upgraded M110A1 entered service, featuring a longer M201 series barrel which gave an increased range.
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Iranian army M110 self-propelled howitzer at a military parade. (Picture source: Borna News Agency)

According to the operator's manual, the M110's typical rate of fire was three rounds per two minutes when operated at maximum speed, and one round per two minutes with sustained fire. The M110 featured a hydraulically operated rammer to automatically chamber the 200+ pound projectile. These rammers were prone to breakdown and generally slowed operation of the gun because the rammers required crews to completely lower the massive barrel before using it. Highly trained and motivated crews could achieve two to four rounds per minute by using the hand-operated manual rammer, which was essentially a heavy steel pole with a hard rubber pad on one end. Using the manual rammer was physically demanding, but crews were not required to lower the barrels nearly as much as with the hydraulic rammer. The M110's range varied from 16,800 meters to approximately 25,000 meters when firing standard projectiles, and up to 30,000 meters when firing rocket-assisted projectiles.

The M110A2 is the latest version with a double muzzle brake, in contrast to the earlier A1 version which had a plain muzzle. The 2nd Battalion 18th Field Artillery (U.S. Army) which Deactivated in 1994 at Fort Sill, Oklahoma, and the 5th Battalion 18th Field Artillery served in Desert Storm with the M110A2 Howitzer, as well as the 142nd Field Artillery Brigade (Arkansas Army National Guard), and 1st BN 181 Field Artillery (Tennessee Army National Guard). Most of the U.S. Army and USMC relied on the M109 series 155-millimeter gun systems during this conflict; sending remaining M110s to reserve or National Guard units. These units then took possession of M109s as they returned from service in the Gulf. M110s were still in service with the 3/92 FA (USAR) and running fire missions at Camp Atterbury as late as the summer of 1994.

The gun system has been retired from U.S. Army service. Howitzers above 155 mm caliber are no longer considered to be practical, as technology has closed the range and firepower gap, and heavier weapon systems require more resources to operate. Gun barrels from retired M110s were initially used as the outer casing in the manufacture of the GBU-28 bunker-buster bomb. The M110A2s were made from refitted M110s or M107 175 mm SP guns.

At the end of the Cold War under U.S. Division Plan 86, all armored and mechanized infantry divisions included a battalion of heavy artillery that included two batteries of M110A2 SP howitzers with six guns each for a total of 12 guns, plus one battery of nine MLRS rocket artillery.

Israel used M110s alongside with M107 during the Yom Kippur War against Egyptian and Syrian forces. Again in 1982 Operation Peace for Galilee, Israel used M110s against PLO and Lebanese allies with deadly effect during the Siege of Beirut.

Turkish army uses M110A2 systems against Kurdistan Workers' Party since  the1990s. Turkish M110A2s also used during Turkish military intervention in Syria, mainly against YPG.

Iran used its M110s during the Iran–Iraq War against Iraqi forces during its offensives against Iraq. And it keeps operating them to date.

Projectiles fired by the M110: M14 dummy, M106 HE, M650 HE rocket assist projectile (RAP), M509 ICM, M404 ICM anti-personnel(airburst), M426 agent GB Sarin, M422A1 W33 (nuclear), M424 High Altitude Spotting Round for M422 projectile