The M43 8in Howitzer Motor Carriage was developed from the M40 Gun Motor Carriage. It arrived too late to see significant service in the Second World War, but it was used during the Korean War.
The M12 155mm Gun Motor Carriage had been developed late in 1941. It carried the French-designed M1917 or M1918 155mm gun on a chassis based on the M3 Medium Tank. A total of 100 were produced, but then went into storage. Late in 1943 the Artillery decided it wanted them for the invasion of France, and a number of them were modernised. At the same time the artillery requested more self-propelled 155mm guns, but the supplies of the M1918 gun had run out. The American M1 155mm gun was heavier and more powerful than the M1918, and the M12 chassis wasn't robust enough to take it.
In January 1944 work began on the T83 155mm Gun Motor Carriage. This was based on a widened M4A3 chassis, with horizontal volute suspension, the engine moved the middle and a new fighting compartment at the rear. Five pilot T83s were ordered in March 1944 and the first was ready for tests at the end of July. After successful tests with the 155mm gun this was replaced with an M1 8in howitzer. Tests with the howitzer were just as successful, and in November 1944 it was decided to complete the last two T83 pilots as the T89 8in Howitzer Motor Carriage.
The T89 was designed to be able to carry either the 8in (203mm) howitzer or the 155mm gun, with interchangeable components and shell storage racks that could take either shell. The pilots were completed in January 1945. Both were tested at General Motors proving ground, and one then went to the Field Artillery Board while the other was prepared for shipping overseas. An order was placed for 576 T89s, but the numbers were reduced after the end of the war. Only 48 were built, 24 from new and 24 by converting M40s. All 48 were complete by September 1945, and the T89 was finally standardized as the M43 8in Howitzer Motor Carriage in November 1945.
The second T89 pilot was the only M43 to see combat during the Second World War. In February 1945 the Zebra mission took a T83, a T89 and some Pershing tanks to France to test them in combat. The T83 and T89 went to the 991st Field Artillery Battalion. Both vehicles received their combat debut during the battle for Cologne, although during this fight the T89 was temporarily armed with a 155mm gun. The 8in howitzer was later reinstalled and used in combat.
A handful of M43s may have reached the front as replacements for worn-out M12s, but their main combat use was in Korea. Both the M40 and the M43 proved to be very valuable during the long stalemate on the 38th Parallel, where the high angle of fire of the M43 allowed it to hit targets on the rear slopes of the many steep hills. The M43 was withdrawn after the Korean War.