Very few paintings of the battlefields that make up the West, North African, and Pacific regions of World War II feel complete without the presence of the venerable M4 Sherman. Produced in greater numbers than any other western tank of its era, it became the backbone of the Allied armed forces. Yet among the seven Sherman models, one stood out for a strange reason. Lengthened about 11 inches to fit its single-type plant, the M4A4 did not carry the usual single-bank engine. Instead, its engine bay housed five Chrysler 251-cubic-inch inline-six engines linked together into a single 30-cylinder unit.
The M4A4 existed because of one of America’s biggest challenges during the war: building enough tanks, fast enough. As US production increased after 1941, demand for tank engines soon outstripped supply. Aircraft manufacturers had priority over radial engines, while other suitable power plants were open to wider competition. To enable the necessary scale of tank production demanded by the US military, Chrysler developed an innovative process that would produce a new variant of the Sherman.
Chrysler’s solution was the A57 Multibank. Instead of designing an entirely new engine, Chrysler combined its proven 251-cubic-inch flathead inline-six engines with a common driveshaft and a center gearbox. The result was a two-ton, 30-cylinder engine that produced nearly 370 horsepower and packed five carburetors, five distributors, and thirty spark plugs into one of the most unusual engines ever put into a production tank.
How a rare engine makes the Sherman unique
Chrysler’s old electrical solution had a direct impact on the tank itself. To accommodate the longer A57 engine, the M4 hull was widened, which required more distance between the suspension bogies than other Sherman models and gave the M4A4 its distinctive silhouette. However, beyond this, the M4A4 retained the qualities that made the Sherman design so successful: good mechanical reliability, simplicity, and a well-balanced combination of mobility, firepower, and protection.
The M4A4 also reflected the broader philosophy behind the Sherman program. Rather than relying on a single engine supplier, the United States deliberately built multiple Sherman models using several powerplants. These include the Continental R975 radial, Ford GAA V8, General Motors twin diesel, and Chrysler’s Multibank. This diversity prevented production problems from disrupting one of the largest weapons production programs in history.
Although developed in the United States, the M4A4 saw little American service. The US military preferred the Ford V8-powered M4A3 and exported many M4A4s to Britain and other allied nations under the Lend-Lease program, where they were known as the Sherman V. A total of 7,499 M4A4s were reportedly produced, 7,443 of which were given to the Allied forces for use during the Italian campaign and the American Northwest.
Loan service and success of M4A4
For all its unusual engineering, the M4A4 proved to be more successful than many initially expected. Although early production was plagued by durability problems, mainly centered on its engine problem, improvements in cooling, piston rings, and exhaust valves gradually increased reliability. By 1944, the engine had successfully passed the US Army’s 400-hour endurance test, and the M4A4 had established itself as one of the most reliable Sherman models, behind only the standard-strength M4A3.
Although its unique power plant suffered from poor fuel efficiency and made repairs more time-consuming than other Sherman models, this disadvantage was often outweighed by overall tank performance. Many foreign mechanics already had a good understanding of small engine maintenance, so once the crew and maintenance personnel became familiar with the unusual structure, the M4A4 gained a reputation for reliability and ease of field operation that surpassed many other Sherman models.
Tank crews themselves also credit the M4A4’s survivability. Since the engine consisted of five independent six cylinders, damage to one bank didn’t stop the car, as Chrysler says the tank can keep going after losing 12 of 30 cylinders. This was of great value to the tanker crews who saw that reduced mobility was directly linked to their survival.
Ultimately, the success of the M4A4 represents one of the industrial solutions of war. Although not ideal, its Multibank engine provided an excellent option for dealing with urgent production problems, and beyond the unusual nature of its engineering roots, the M4A4 Sherman was admirably successful in its role as part of the mass production and use of world war machines that contributed greatly to the Allied victory.