By the end of the Korea War (1950-1953), the American Army was in need of modernization to replace many of its weapon systems that dated back to World War 2. One need ultimately became air-portable, tracked artillery systems that could be transported over distances to the awaiting army units. A requirement put forth by the US Army became a self-propelled artillery platform to which the heavy industry-minded Pacific Car and Foundry went to work on developing several pilot vehicles which ultimately produced a range of possibilities, the Army then electing to forge ahead with two promising designs that would become the M107 and M110 self-propelled artillery platforms. Key differences between the two would be the M107's 175mm gun and the M110's 203mm gun though both would utilize the same chassis and gun mounts between them for economical and logistical reasons. The initial batch of M110 vehicles was completed in 1962 and formal acceptance into the US Army and US Marine Corps inventory soon followed.
The M110 was more or less of a conventional design featuring the main gun mount fitted atop a tracked chassis yielding five large rubber-tired road wheels to a side. There was a drive sprocket mounted to the front of the track system though, interestingly, no track return rollers or track idler of any kind was used. The vehicle sat atop a torsion bar suspension system and power was supplied by a single Detroit Diesel / General Motors 8V71T series 8-cylinder, liquid-cooled, supercharged diesel engine developing 405 horsepower at 2,300rpm. Top speed was listed at 34 miles per hour with a 325 mile range. Operational weight was approximately 31 tons. She fielded a running length of 10.8 meters with a width of 3 meters and a height equal to 3 meters as well.
Primary armament of the M110 was its massive 203mm (8") howitzer main gun mounted on the center rear of the hull roof (there was no true superstructure per se). The gun could be elevated between +65 and -2 degrees with 30-degrees traverse to the left or right. 360-degree traversal was only possible by rotating the entire vehicle in a new direction. There were no secondary weapons fitted to the vehicle for the M110 was never intended to fight enemy forces at the frontlines, instead utilizing its powerful cannon to lob shells at targets or areas. Ammunition types afforded to M110 crews included the M14 "Dummy" round, the common M106 High-Explosive round, the M650 High-Explosive rocket-assisted projectile for increased assault ranges, the M404 ICM (Improved Conventional Munition) anti-personnel projectiles intended to explode above the target area with some 180 grenades being launched about, chemical gas projectiles and nuclear-tipped rounds. Only two of the large 203mm projectiles could be carried on the M110 vehicle, the rest of her ammunition supply towed by a support vehicle. A dozer-type spade was fitted to the rear of the hull to counter the 203mm gun's inherently violent recoil when firing - the M110 firing from a stationary position. The powered spade was raised from the ground and stowed when traveling.
Of the thirteen-man crew, only the driver sat in relative protective comfort, his position to the front left side of the hull. The remainder of the - five of which rode with the M110 proper and the other eight in a support vehicle - included a pair of gunners and a pair of loaders. These personnel maintained their respective positions in the open-air rear portion of the vehicle. Categorized as a "self-propelled artillery" system, the M110 was never intended to fight as a direct line-of-sight combat vehicle, hence her open-air gun platform approach and armor protection being no more than 13mm at its thickest. Instead, the crew could utilized the 203mm main gun's excellent range to strike at targets from miles away.
The M110 was fielded with a support vehicle fitting additional crew and the main 203mm ammunition supply. In the US Army inventory, this role was fulfilled by the M548 tracked vehicle while in the British Royal Army inventory, this became the Alvis-produced six-wheeled FV623 "Stalwart". Eight of the thirteen-man M110 crew were transported with these vehicles. In addition to 203mm projectiles, the support vehicles also carried the required charges and fuses for each round.
The M110, with its original M2A2 series 203mmmain gun, was firmly entrenched in the US Army inventory by the mid-1960s. It was not until 1977 that a revised form appeared as the newly-standardized "M110A1". The M110A1 differed from the original production model by implementation of a longer M201 series 203mm gun barrel for increased ranges (no muzzle brake). Within a few years, the M110 was modified yet again to produce the "M110A2" designation standard which was nothing more than the M110A1 with a double muzzle brake and the ability to fire other types of projectiles beyond the standard HE and anti-personnel rounds. Capability to fire the M509 ICM projectile was also introduced with the M110A2 model and some original M110s were also upgraded to strengthen M110A2 numbers.