The M44 Self-Propelled Howitzer was adopted by the U.S. Army to replace the outmoded stock of M41 Howitzer Motor Carriages. Both fielded a type of 155mm howitzer gun though the preceding M41 was based on the World War 2-era M24 "Chaffee" Light Tank and the newer M44 built upon the components of the M41 Walker Bulldog Light Tank. The M44 was not an outright success and faced a major rebuild program before the end of her tenure.
T99E1 served as the series pilot vehicle and attempted to retain many of the underlying workings of the M41 tank as possible. The five road wheels of the M41 became six road wheels in the M44 to which the track idler was deleted and the sixth road wheel pairing serving in this role. The drive sprocket was held at front along with the relocated engine compartment which allowed for a fixed, fully-enclosed armored superstructure to be fitted over the rear. Four track return rollers were used in the track-over-wheel arrangement. The crew numbered five and included the driver in the hull superstructure as well as the commander, gunner and a pair of ammunition handlers. Armor protection reached 12mm in thickness.
The vehicle was outfitted with a vehicle version of the 155mm M114 land howitzer (as the T97E1). This weapon was introduced during 1942 and over 10,000 units were produced into 1953. The weapon utilized a slow-cone interrupted screw breech design with a hydropneumatic recoil system. The recoil mechanism was slight modified so as to fit in its new mountings. It could lop its 155mm projectiles out to 16,000 yards with a muzzle velocity of 1,850 feet per second. Fitted to the M44 hull superstructure, the barrel proved short in appearance as no hull overhang was seen. Defense was through a single 0.50 caliber M2 Browning heavy machine gun as well as any personal weapons carried by the crew.
The M44 also retained the Continental AOS-895-3 series 6-cylinder gasoline engine of 500 horsepower seen in the M41 tank. It also rode upon its torsion bar suspension system. Road speeds reached 35 miles per hour with operational range being under 100 miles.
Interestingly, the U.S. Army elected for production to begin even before the T99E1 had completed its testing. It was then realized that the enclosed design of the hull superstructure trapped dangerous gasses during the firing action while other issues also emerged. By this time, 250 units were already completed which led to a halt in further production.
Engineers then looked to solve the major problems and adopted an open-air hull superstructure. This also allowed for a better working space for the crew as well as introducing natural light. However, it also exposed them to the elements as well as battlefield dangers. The howitzer was also replaced with the T186E1 developmental series of same caliber. With the changes in place, the vehicle was reborn under the new designation of T194 Self-Propelled Howitzer. A conversion program was then enacted to bring the existing 250-strong stock of T99E1-based vehicles to the T194 standard. After formal adoption, the system then became known as the M44 SPH. Still another change greeted the series when the M41 Walker Bulldog was handed its improved AOS-895-5 engine - the M44 fleet followed suit and were accordingly upgraded in turn to become the M44A1.
The M44 arrived too late to see combat service in the Korean War (1950-1953). It was only ever exported to allied Italy.