The M4A4 Sherman is the standard US medium tank, built by the Tank Yard.
The US lagged behind the other combatants in armor development prior to the war; in 1939 their M2 medium tank was merely an enlarged variant of their then-standard M2 light tank armed with a 37mm gun. Developments in Europe convinced planners that a 75mm-armed medium tank was necessary; in their haste to get such a tank operational the US had no time to design a new turret and instead entered the war with the M3 Lee, which mounted a 37mm turret gun and a hull-mounted 75mm. The M4 Sherman evolved from this design, deleting the 37mm gun and mounting the 75mm in a new turret. Over 50,000 M4 Shermans would be produced both for the US Army and Marine Corps, as well as dozens of Lend-Lease recipients including Great Britain, which fielded Shermans in most of its armored units.
When first deployed in the North African theater in 1942 the Sherman was handily capable of taking on the Pzkw. III and IV tanks it faced; its armor could protect against shots from German 37mm and 50mm guns and its lower-velocity 75mm gun was capable of defeating German armor. The introduction of the Tiger I, Panther, and upgraded Pzkw. IV tanks armed with the KwK 40 gun quickly outclassed the Sherman, making it dependent on its superior speed and numerical superiority to defeat German armor. Due to the US doctrine of assigning tank destroyers to antiarmor duties and with the focus on production output, several projects to replace the Sherman such as the T23 medium tank design and M26 Pershing heavy tank were cancelled or delayed, along with upgrade programs such as fitting a 76mm gun. As a result, all Shermans landed in Normandy in June 1944 and 50% of the US Shermans in Europe at the end of the war were still armed with the 75mm. Improvements such as wet ammunition stowage improved crew survivability in case of a hit, but Shermans and their crews still fell in large numbers during the European campaign; the American 3rd Armored Division lost 1,348 Shermans in combat between June 1944 and May 1945 (with 682 of those being unsalvageable). 3rd AD had a posted full strength of ~280 Shermans.
The Sherman exemplifies the strengths and weaknesses of US armor units in general; it is fast and cheap with a good anti-infantry punch. Its rate of fire and powerful high-explosive shells make quick work of infantry, light vehicles, and structures. Against German armor it suffers badly; its 75mm main gun is useless against the frontal armor of the Tiger and Panther tanks even at point-blank range, while German 75mm and 88mm guns can shred the Sherman long before it has a chance to shoot back. In order to defeat heavy German tanks it needs to be fielded in far greater numbers and use its superior speed to close with and outflank them, or be hidden behind terrain where it can ambush German tanks from the sides or rear at close range.