The Panzer III and Panzer IV's success in the French campaign led the U.S. Army to immediately order a new medium tank armed with a 75 mm gun in a turret. This would be the M4 Sherman. However, until the Sherman was in production, an interim design with a 75 mm gun was urgently needed. The M3 was the solution. The design was unusual because the main weapon, a larger caliber, low-velocity 75 mm gun, was mounted in an offset sponson within the hull. This gave the gun a limited traverse. A small turret with a lighter, high-velocity 37 mm gun sat on the tall hull. An even smaller cupola on top of the turret held a machine gun. The British ordered the M3 when they were refused permission to have their tank designs (the Matilda infantry tank and Crusader cruiser tank) made by American factories. British experts had viewed the mock-up in 1940 and identified several flaws — the high profile, the hull mounted gun, radio in the hull, smooth tracks, the amount of armor with insufficient attention to splash-proofing the joints. The British agreed to order 1,250 M3, to be modified to their requirements - the order was subsequently increased with the expectation that when a superior tank was available it could replace part of the order. Contracts were arranged with three U.S. companies, but the total cost was approximately 240 million US dollars. This sum was all of the British funds in the US and it took the Lend-Lease act to solve the financial problems. The prototype was completed in March 1941 and production models followed with the first British specification tanks in July. The British cast turret included a bustle at the back for the Wireless Set No. 19 radio. It had thicker armour than the U.S. one and removed the U.S. cupola for a simple hatch. Both U.S. and British tanks had thicker armor than first planned. The British design required one fewer crew member than the US version due to the radio in the turret. The U.S. eventually eliminated the full-time radio operator, assigning the task to the driver. The British realized that to meet their requirement for tanks both types would be needed. The U.S. military utilized the "M" (Model) letter to designate nearly all of their equipment. When the British Army received their new M3 medium tanks from the US, confusion immediately set in, as the M3 medium tank and the M3 light tank were identically named.