The M43 Howitzer Motor Carriage was a World War 2 (1939-1945) development and a further evolution of the M40 Gun Motor Carriage line. The two were, therefore, closely related products from the Pressed Steel Car Company and emerged in 1945. The hull, chassis and running of the M40 was retained (itself taken from the M4 Sherman line) though the M43 mounted the massive 203mm howitzer system and early trials were carried out through the T89 Howitzer Motor Carriage pilot vehicle. After their acceptance in November of 1945 - following the end of war - the T89 emerged as the standardized M43. 576 units were part of the original U.S. Army order but the end of the war reduced total procurement to just 48 - twenty-four of these completed by war's end and a further twenty-four converted from existing M40 systems. The single pilot vehicle did, in fact, see combat service before the close of the war though its production brethren were not used in anger until the Korean War (1950-1953).
The finalized vehicle was a 41.5-ton product requiring a crew of eight with the gunnery section operating in an open-air environment (the driver was in the hull). The main gun was the M115 land howitzer standardized in 1941. It fired a 240lb shell at a muzzle velocity of 1,925 feet per second out to 10.5 miles away. It was typically arranged atop an eight-wheeled, twin-axle carriage system that included the tow arms, recoil mechanism and mounting hardware. Beyond the carriage, this was carried over to the M43 vehicle. A rear-mounted recoil support was lowered prior to firing to help counter some of the violent effects of the action.
Drive power was through a Continental R975-C4 engine of 400 horsepower which, as a self-propelled vehicle, allowed the M43 a maximum road speed of 24 miles per hour and a driving range out to 105 miles. The performance was eventually found wanting as the heavy vehicle struggled to keep up for mechanized forces of the U.S. Army. As a stationary battlefield artillery piece, however, the M43 did not disappoint in Korea.