Thursday, May 26, 2011

From the Pages - Background the M4 Sherman

It was not the most heavily armored tank. In truth, it was tall and ungainly, and its firepower simply couldn’t match the German tanks it faced. 

What it was, however, was a prime example of America's dedication to innovation and soon-to-be-legendary manufacturing capabilities. And by dint of sheer numbers and downright reliability, the M4 Sherman became the winning workhorse of World War II—from the fields of Europe to the islands of the Pacific.

In the following excerpt from M4 Sherman at War, Michael Green and James D. Brown detail the earliest days in the M4's storied legacyfrom the design and manufacturing changes that set it above its predecessor, the M3 Lee/Grant, to its trial by fire in the deserts of North Africa.
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Beginnings of the M4 Medium Tank
On August 31, 1940, the Armored Force Board released detailed characteristics for a new medium tank armed with a turret-mounted 75mm gun. Six months later, the chief of Ordnance requested that Aberdeen Proving Ground proceed with the design of the new tank following completion of upgrade work on the M3 tank series. The chief of Ordnance directed that automotive features of the new medium tank—including the air-cooled gasoline-powered radial powerplant, powertrain, suspension, and track—should be essentially those of the M3 medium tank.

The principal change was moving the hull-mounted 75mm gun into a turret. Also agreed upon was the use of welded RHA or CHA hulls. Increasing the thickness of the vehicle’s armor, while at the same time reducing the number of crew members, was also considered an important goal in order to up-armor the tank without increasing the vehicles’ gross weight.

In June 1941, the Ordnance Committee ordered the building of a full-size wooden mockup and a pilot model of the new tank designated the T6. Upon completion of the wooden mockup, followed by a few design changes, Aberdeen Proving Ground started to manufacture a complete pilot tank with a CHA hull and turret. Rock Island Arsenal started building a pilot tank with a welded RHA hull. The turret would come later, as the turret design was not yet ready for production.

Aberdeen Proving Ground rolled out its 30-ton T6 pilot tank on September 2, 1941. After representatives of the Armored Force and the Ordnance Department inspected the new tank, two major changes were ordered. The first was to replace the ballistically inferior side escape doors with an escape door in the floor just behind the assistant driver’s position. The second was to eliminate the .30-caliber machine gun CHA cupola from the top of the vehicle’s new turret.

On September 5, 1941, the Ordnance Committee ordered production of the M4 medium tank. Just one month later, the characteristics were amended to add a .50-caliber antiaircraft machine gun on the top of the tank turret. Another change was to fit a .30-caliber gun in a ball mount, which would be operated by the assistant driver, in the vehicle’s front hull. Finally, two fixed forward-firing .30-caliber machine guns, which would be operated by the driver, were to be mounted in the front hull. A directive issued in March 1942 soon dropped the hull-mounted guns from the design.

New Designations
By November 1941, the manufacture of M4 pilot tanks had begun. In December, the Ordnance Committee designated the welded-hull versions as M4 and designated the cast hull versions as M4A1. Aberdeen Proving Ground used the pilot T6 (by now an M4A1) for further development.

In British Army service, the M4 became the Sherman I, and the M4A1 became the Sherman II. Although the name Sherman did not come from the U.S. Army, it did become popular with many U.S. Army tankers fighting in Europe during World War II and shows up in army reports from the period. In the decades after the war and to this day, it has remained its primary name.

Some M4 series crewmembers called their vehicles the “M4” or just the “medium.” Tom Sator, a loader on an M4 series tank in Northwest Europe during World War II, remembers calling them either a “75” or “76,” based on the size of the main gun mounted on the vehicle. When the officers were not around, Tom said the crews often referred to their tanks as “rolling steel coffins.”

In late 1941, the U.S. Army’s main concern was that there was no interruption in the production of tanks when the changeover from the M3 to the M4 series took place. The Ordnance Department took delivery of the first series production cast-hull M4A1 from the Lima Locomotive Works in February 1942. The second vehicle went to Great Britain, bearing the name “Michael” in all capital letters on its side, in honor of Michael Dewar, head of the British Tank Mission in the United States. This shipment was influenced by the U.S. government’s cancellation of a British order for four hundred M3 medium tanks so that Lima could build more M4A1s.

In March 1942, the Pressed Steel Car Company started building M4A1s, with Pacific Car and Foundry Company starting in May of that same year. Production of the M4A1 would continue at the three firms until December 1943, with 6,281 units built.

In July 1942, the Pressed Steel Car Company started production of M4s. Four other manufacturers soon joined in, including Baldwin Locomotive Works, the American Locomotive Company, the Pullman Standard Car Company, and the Detroit Tank Arsenal.

Near the end of its production run of M4s, the Detroit Tank Arsenal combined a CHA front hull with a RHA rear hull. Many describe this hybrid hull arrangement as the composite variant.

M4 and M4A1 Differences
Other than a few minor differences resulting from the welded upper hull design of the M4, the M4A1 was almost identical to it, with the same engines, powertrains, and suspensions. Due to the more angular shape of the M4, it had room for ninety-seven rounds of 75mm main gun ammunition versus only ninety rounds of main gun ammunition in the more rounded hull of the M4A1.

In the original welded-hull M4 tank, the ninety-seven main-gun rounds were divided between the turret and hull. Twelve vertically orientated rounds were arranged around a raised step on the lower turret basket wall, with another eight stored horizontally in a ready rack on the turret basket floor underneath the main-gun breech mechanism. Behind the loader’s seat in the left sponson (the horizontal hull plate that overhangs the track) were fifteen main-gun rounds stored horizontally. Two opposing sets of storage racks were located on the right sponson. The front-most rack contained seventeen main-gun rounds stored horizontally. The rear rack contained fifteen main-gun rounds also stored horizontally. Another thirty rounds were stored in a horizontally orientated storage rack underneath the turret basket floor, accessible only by the assistant driver. 

The ammunition storage arrangement for the cast-hull M4A1 differed only in the number of main-gun rounds stored on the left sponson storage rack. Instead of the twelve main-gun rounds in the welded-hull M4 tank, the M4A1 had room for only eight main-gun rounds.

New Engines
As with the M3 series, the lack of enough air-cooled gasoline-powered radial engines proved to be a serious problem for the M4 series. The Ordnance Department was forced to use whatever motive power was available.

The Ordnance Department took the twin liquid-cooled GM diesel engines installed in the M3A3 and M3A5 and stuck them in a welded-hull M4. Reflecting various modifications made to the tank—primarily in the engine compartment—it designated it the M4A2. Production began in April 1942 at a number of different manufacturers and continued until May 1944, with 6,748 units built armed with the 75mm main gun. In British Army service, the M4A2 became the Sherman III.

In March 1942, the U.S. War Department issued a policy stating that only gasoline-powered M4 series tanks would go overseas to American forces. Diesel-powered M4 series tanks were for training purposes within the United States only, or for supplying to Allied nations also fighting the Axis. Despite this ban on sending the M4A2 overseas with American fighting men, when the Marine Corps initially requested M4 series tanks, it ended up with about two hundred M4A2s in late 1943.

M4A3 Tank
The only practical substitute for air-cooled radial engines proved to be the Ford GAA liquid-cooled gasoline-powered engine. The Ordnance Department installed it in a welded-hull M4 and designated the tank the M4A3. In outward appearance, the M4A3 differed from others in the series only in its rear engine compartment arrangement and some other minor features.

The eight-cylinder Ford GAA was an experimental aircraft engine with high output power for its size and weight. Maximum gross power was 500 horsepower at 2,600 rpm. The net power as installed in the M4A3 was 450 horsepower at 2,600 rpm.

If sufficient production capacity had existed for the Ford GAA engine, the Ordnance Department would have replaced the air-cooled radial engine across the entire M4 fleet. However, not everybody was convinced the Ford GAA was the perfect solution. According to Captain Charles B. Kelly of the 2nd Armored Division in a wartime report, “the Ford engine is considered very good,” he writes, but then adds, “if you’d add two more cylinders you’d have an engine.”

Production of the M4A3 began at Ford in June 1943 and continued until September 1944, with 1,690 units built armed with the 75mm main gun. As with the M4 and M4A1, the M4A3 weighed about 33 tons. It first entered service with the U.S. Army unit in the European Theater of Operations (ETO) in the summer of 1944, and soon became the preferred M4 series tank due to its superior engine. By the end of the war in Europe, almost half the army’s inventory of tanks consisted of some version of the M4A3 tanks. It entered into Marine Corps service in late 1944.

The British Army received only seven M4A3 armed with the 75mm main gun from the United States. The British used them only as test vehicles and designated them the Sherman IV.
Skip Warvel, curator of the Indiana Military Museum, compares the radial engine to the Ford GAA engine in the M4A3 tank: “With a Ford V8, you can put it in second gear and start at idle speed, no problem. If you try that in a radial, nine times out of ten, you’ll kill it. It just doesn’t have the power to move 62,500 pounds forward at idle. So, from a driving standpoint, it’s much easier to drive the Ford engine than the radial engine.”

The M4A4 Tank
Desperation also drove the Ordnance Department to okay the mounting and installation of an improved version of the M3A4’s Chrysler A57 Multibank gasoline-powered engine into welded-hull M4 series tanks. Like the M3A4, the large and bulkier powerplant mandated a lengthened hull and suspension system. Ordnance Department tests showed the A57 Multibank was the least satisfactory of the engines selected for the M4 series and recommended that when a sufficient number of other types of engines became available, its production would come to an end.

With no interest in the A57 Multibank version—designated the M4A4—except for stateside training purposes, the American army decided to provide most of them to the British Army, as had been done with the M3A4 tank.

According to author David Fletcher in his book titled The Universal Tank: British Armour in the Second World War Part 2, automotive engineers from the British Tank Engine Mission looked with absolute horror on the A-57 Multibank–powered tanks being offered to it. He writes, “Even so, Britain took most of the 7,500 M4A4s built before production ceased in September 1943 (including 1,400 originally allocated to the U.S. Army for training) and found them to be quite serviceable if one overlooked the maintenance difficulties. Indeed it probably accorded well with the British temperament to make a virtue from trying to get the best out of the worst possible engine.”

In British military service, the M4A4 became the Sherman V. Chrysler completed 7,499 units between July 1942 and September 1943. The lengthening of the M4A4 and the larger and heavier powerplant drove the vehicle’s weight to almost 35 tons. 

Due to a serious U.S. Army shortage of M4 series tanks during the Battle of the Bulge (December 1944 to January 1945), the British Army returned a number of M4A2 and M4A4 tanks to the U.S. Army. Most went on to see service with the American Third Army, under the command of General George S. Patton.

The M4A6 Tank
The only other M4 series tank to see the mounting of an alternate powerplant was the composite hull M4A6. It featured a Caterpillar Tractor Company modification of a Wright G200 air-cooled, gasoline-powered radial turned into a diesel engine with a fuel injection system. Originally referred to as the Caterpillar D200A, it later became the Ordnance Engine RD-1820, denoting a radial diesel with displacement of 1,820 ci. Unlike the other engines in the M4 series, the new powerplant in the M4A6 could operate on variety of petroleum products ranging from crude oil to gasoline, making it the first example of a multifuel tank powerplant.

Chrysler began production of the M4A6 in October 1943. However, the Ordnance Department decided to discontinue production in February 1944 after only seventy-five units were completed. The cancellation was based on changing military requirements and a decision to concentrate on building more of the gasoline-powered M4A3 tanks.

All of the M4A6 tanks came with the same unusual combination of a cast-hull front mated to a rear three-quarter-welded hull, as did some late production M4 tanks built at the Detroit Tank Arsenal and labeled the composite variant.

M4 Series Combat Debut
Like the M3 series, the M4 series would see its first combat action in North Africa with the British Army. In September 1942, during the Battle at El Alamein, a small detachment of German Army medium tanks ran into the 2nd Armored Brigade, which was just recently supplied with the M4 series tanks. After a brief engagement that left several tanks burning on both sides, the German Army tanks withdrew.

After the Battle of El Alamein, the number of M4 series tanks in British Army armored units increased so dramatically that it soon became its most widely used and highly regarded type in service.  A statement from a senior British Army officer that showed up in a U.S. Army report, titled “Tankers in Tunisia,” asserts, “In my opinion the Sherman is the finest tank in the world, better than anything else we have and also better than anything the Germans have. It will be the best tank for the next five years.”

The very confident U.S. Army suffered its first defeat with the M4 series in North Africa in December 1942. In an inauspicious beginning, a platoon of five tanks from the 2nd Armored Division went up in flames from a combination of accurate German tank and antitank gunfire. This same scenario took place a couple of months later on a much larger scale, when the German Army punched a hole through American II Corps’ lines and inflicted terrible losses in both men and equipment. Over one hundred American tanks, most of them M4 series, littered the barren North African battlefield in its aftermath.

Lieutenant Colonel L. V. Hightower, the executive officer of the 1st Armored Regiment of the 1st Armored Division, which took such a drubbing from the German Army, explains in an after-action report how the Germans prevailed in that series of encounters: “Generally they try to suck you into an antitank trap. Their light tanks will bait you in by playing around just outside effective range. When you start after them, they turn tail and draw you in within range of their 88s. First, they open up on you with their guns in depth. Then when you try to flank them, you find yourself under fire of carefully concealed guns at a shorter range. We’ve just got to learn to pick those guns up before closing in on them.”

Lieutenant Colonel E. A. Russell Jr., also an executive officer of the 1st Armored Division, in a June 10, 1943 report, says about one of the problems that plagued the U.S. Army during its time in North Africa—that of over-confidence:

In the initial stages of the operation of this command in November and December 1942, such over-confidence resulted in the rapid whittling down of a medium tank battalion [fifty-three tanks] to less than twenty tanks within a few minutes of actual combat. Another incident: shortly afterward a platoon of M4 replacement tanks with new crews, upon being assigned a mission and given warning of the effect of enemy fire against the M3s, charged gloriously but vainly up a hill only to lose four of five tanks from AT [antitank fire].

Talking to the platoon leader afterwards he truthfully explained that, one he was confident that present AT guns were ineffective against the new M4 and two, that his method of approach was based on an approved solution given under similar circumstances on maneuvers.

Despite their losses in North Africa, most American tankers considered the M4 series a fine tank and more than sufficient for any job at hand. From a U.S. Army report comes this quote from a Sergeant Becker, who saw combat in North Africa: “I like the M4. I look at the German tank and thank God I am in an M4.”

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