After World War II, most US Army armored units were equipped with a mix of M4 Sherman and M26 Pershing tanks. Designed initially as a heavy tank, the M26 Pershing tank was reclassified as a medium tank postwar. The M26 was a significant improvement over the M4 Sherman in firepower and protection. Its mobility, however, was deemed unsatisfactory for a medium tank, as it used the same engine that powered the much lighter M4A3. Its underpowered engine was also plagued with an unreliable transmission.