And the need to get something in production ASAP.
People tend to forget the #1 tank in NUMBERS in the German Army, as late as 1945 was the Panzer III Series of Tanks, NOT the Tiger or even the Panther. In actual tanks (Excluding tank destroyer variations, by 1945 the Number # 1 Tank was the Panzer IV). The Germans were still using the Panzer III as a Tank in 1945 and its number exceeded the Tigers both in units and in Production (Through production of Panzer III Tanks ended in 1943, the Tank Destroyer variations continued till the end of the War) Both the Panzer III and the Panzer IV were inferior to the Sherman (Through the Up-gunned Panzer IVs of the later war years had a more powerful gun than the Sherman).
TOTAL German tank production for WWII was only 50,439 units (and that includes Panzer Is, Panzer IIs and T-38 light tanks). Russian T-34 production alone exceed this number (Total T-34 produced during WWII 57,339). M-4 Shermans and its Tank Destroyer Cousins exceeded this number (Total Sherman produced 48,966 with an additional 9030 Tank Destroyers produced). If you take out of the German Production the Panzer 1s, and IIs and the T-34 Light Tank, total German Tank Production was only 38,515 and this included tanks MADE before the war and destroyed in the years before D-day.
My point is even in France the chances of a Sherman meeting a Tiger was slim (Over half the tanks in France by 1944 were Panthers, the Panzer IIIs and IVs were in Russia, the Panthers ended up in France do to the nearest of France to the Panther Factory in Germany). The Panther could knock out a Sherman why before a Sherman could knock out a Panther, but once in range the Panther could be destroyed by the 75mm gun of the Sherman. The Tiger was another story, the 75mm Sherman gun could NOT penetrate the Tiger's armor, thus against the Tiger the Sherman losses were huge. The problem as the Germans had a problem getting the Tiger to the battlefields. The Tiger could NOT go on standard trains for it was to wide (The Panther was design to fit into any railroad tunnel, the Tiger could not). Once at the battlefield the Tiger was to heavy for most bridges which restricted their movements compared to the Shermans and Panthers. Last the Tiger ate up fuel compared to the Sherman and Panthers, fuel the Germans did not have to spare.
Thus the Sherman, with its limitations, became supreme in the battlefields of France in 1944. The Sherman ease of maintenance, lighter use of Fuel and ability to be transported on most of the bridges and tunnels of France permitted it to go anywhere it wanted to go. The Panther was its greatest threat, but a Tank the Sherman could knock out (If equipped with the 76mm anti-tank gun, which over 1/2 of all Shermans in France in 1944 had). The Tiger's lack of speed, reliability, and numbers made it a minor factor on the Battlefield. The Tiger's limitations were to great for its assets of a great gun and heavy Armor to overcome.
My point was staying with the Sherman, with its limitation was a good decision on part of the US. I wish the US Armor Corps would have put on the 17 pounder British Anti-Tank gun that the British did instead of the 75 and than 76mm gun that the Sherman came equipped with. The failure to adopt a powerful Anti-tank Gun was the result of another Mistake of the US Army, the US Army Adoption of the "Tank Destroyer concept" that said Tanks do not engage Tanks, Tank Destroyer engaged Tanks (Someone in the US Army forgot to tell the Germans of that rule who engaged Shermans with their tanks). Had these mistakes NOT been made a lot of Americans would not have been killed, but at the same time the price of the mistake was small given the lack of Fuel and Tanks available to the Germans.
Lets look at some numbers:
Total Tiger Series Tanks produced: 1,937
Total Panther Series Tanks Produced: 6,557
Total Panzer IV Series Tanks Produced: 13,522
Total Panzer III Series Tanks Produced: 16,409
T-34 Production:
34,780 with the 76mm Gun
22,559 with the improved 85mm Turret and gun
57,339 TOTAL T-34 produced
US Tank Production M4 Sherman only:
33403
10883 with 76mm Gun
4680 with short barrel 105mm Howitzer
48966 M$ Sherman produced during WWII with an additional 9030 Tank Destroyers produced.
German Tank production:
http://en.wikipedia.org/wiki/German_tank_production_during_World_War_IISoviet Tank Production:
http://en.wikipedia.org/wiki/Soviet_armored_fighting_vehicle_production_during_World_War_IIUS tank production:
http://en.wikipedia.org/wiki/American_armored_fighting_vehicle_production_during_World_War_II