The M26 Pershing is an American heavy tank that was designed to be an improvement upon the M4 Stuart, but which saw limited action during WWII. Production and development of the Pershing was delayed by three main factors. 1) The US Army ran under the Tank Destroyer doctrine, and therefore had no doctrinal use for Heavy tanks. 2) A heavy tank would affect America's 3,000 mile supply line to Europe, and would cause considerable problems in terms of transport, supply and servicing. 3) Complacency also played a role, as the M4 was capable of dealing with the common Panzer III and early Panzer IV tanks. A lack of foresight meant that the US tank designers and manufacturers failed to anticipate future German tanks, such as the Tiger I and the Panther, which would be capable of pushing back the M4s. In contrast, both Britain and Russia were in an arms race with Germany to try and stay one step ahead with their tanks. The result of the delays is that the Pershing didn't even enter production until late in 1944, and saw very little action in WWII as a direct consequence of this.