The M4 Sherman Tank was the most commonly used American tank during WWII. Between the years of 1942-1945, a little less then 50,000 Sherman tanks were produced. The Sherman tanks were used in the majority of battlegrounds during the time span of the war; it was used by the British, French, Chinese, and even the Soviets. Initially designed to replace the M3 Grant/Lee, the model proved itself somewhat effective against the German Mk II and Mk IV Panzer's, but was completely outclassed by the Tiger, Panther, and King Tiger tanks. 
With World War II beginning in 1939, the United States lagged far behind the majority of the European states in the development of tank technology and armored warfare. However, with the fall of France in 1940, U.S. military personnel became convinced that the military needed a new main battle tank at least equal to that employed by the Germans. Thus, in July of 1940 the War Department authorized the development of the M3 General Grant, completing the design a year later in 1941. Though it was used by British forces in Africa in as early as 1941, it suffered from a significant design flaw: the 75-mm gun carried in a sponson in the right front of the hull could traverse only 15 degrees- a major disadvantage in tank battles. Thus, redesign took place, and by the late 1942, production of the M3 General Grant ceased and the M4 Sherman went into full production. 
The design for the M4 Sherman went into full production on September 5th, 1941. Before production of the M4 increased, the M4 was revised to include a 12.7 mm heavy-barrel browning machine gun on the turret for anti-aircraft defense. A .30 caliber machine gun was then added to the upper hull bow plate, and an additional paired caliber bow-mounted, driver-operated machine guns were implemented. Eventually however, the paired caliber bow-mounted machine guns were removed due to costs. Initial Sherman's were produced with the M4 sporting a welded hull and the M4A1 sporting a cast hull. Large in size, with a distinctive broad, sloped frontal hull armor, it was designed with protruding position hatches for the driver and bow gunner. Additionally, the engine was attached to the rear to ensure that if the tank were to be hit head on, the tank would still operate. This is a design practice still used in today's modern battlefields. 
For the majority of the vehicles at the time, the Sherman ran on diesel, a safer and less flammable fuel then gasoline. However, this did not stop the Sherman from bursting into flames. Using a 400-horsepower gas engine with the combined ammo on board, the M4 Sherman was susceptible to enemy fire that could potentially set the 5 man crew ablaze from the interior. Unfortunately, for many users of the Sherman, this became a reality when coming into opposition with Axis forces: the German Tiger Tank was a superior model capable of scorching the Sherman with its 88-millimeter gun. A single round could punch through the Sherman's comparatively thin armor, and set off a simple chemical reaction that would leave its crew burnt to ash. Hence, the Sherman was nicked named after the cigarette lighter Ronson, because "it lights up the first time, every time." 
But despite being mechanically inferior by design to the German Tiger tank, it strength did not lay within one-on-one engagement; rather, the Sherman's strength was in its numbers. It was a symbol of the United States' industrial prowess during WWII, a time in which factory output was pivotal to the success of war efforts. Where companies such as the Pullman Car Co. to Ford Motors were able to produce nearly 50,000 Shermans, the German Tiger tank's costly design only saw about 1,300 reach the battlefields. If a Tiger was lost, it was a pivotal loss to the German military; but if a Sherman was destroyed, the U.S. could affordably replace it. This is not to say that the Sherman was not an effective engine of war: it was fully capable to laying down heavy suppression fire, and could easily level buildings that sheltered squads of German troops. 
Regardless of its effectiveness on the battlefield against infantry or armored opponents, the M4 Sherman was a staple figure upon the battlefields of WWII. Easy to manufacture and widely accessible, the Sherman tank was a marvel of engineering for its time. It provided allied forces with heavy support, and was a leading tank in spearhead assaults. Within the history of technology and engineering, the M4 Sherman tank is a historical figure; a precursor to the development of American armored vehicles to come.