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Section Leaders:
The Early M4A1 and M4 Medium Tank By
Dan “dano6” Kowaleski
Introduction: Upon the completion of the development of the M3, the US armored force immediately set about the initial development of the M3's successor. The new tank would be designed to correct the major flaw of the M3 series, a limited traverse, sponson-mounted 75mm gun. The new tank was designed to use the 75mm gun in a full traverse turret. This new tank would soon be called the M4 "General Sherman" or Sherman for short.
Early Development: In early 1941, the US armored force decided that the basic M3 chassis would be used for the development of the new M4 tank. As many parts from the M3 would be used as possible in order to expedite production as time was of the essence. Crew size of the M4 was reduced to 5 men due to the elimination of the sponson mounted 75mm gun. The M4's crew now consisted of a commander, gunner, loader, driver, and bow gunner. The first test vehicle, the T6, was produced by Aberdeen and inspected by the US Armored Force on September 2, 1941. It was armed with the M2 75mm gun in a full power traverse turret. The M2 was extremely out of balance in the mount designed for the longer barreled M3 75mm. The M2 gun was extremely difficult to depress due to the weight of the recoil mechanism and the breech. Double counterweights were added to the barrel in order to balance the gun. The front hull was equipped with 3 .30 caliber machineguns. Two of the guns were set in a fixed firing position facing directly forward and the third was set in a rotation ball turret to allow the bow gunner adjustment of fire. The T6 test vehicle was standardized as the M4 on September 5, 1941. On December 11, 1941 vehicles with the welded hulls retained the M4 designation, while vehicles with the cast upper hull were given the M4A1 designation. The welded upper hull design lagged behind the cast design due to engineering concerns with the weld lengths and the amount of plates to be used to construct the M4. The Rock Island Arsenal was placed in charge of the production of the welded-hull test vehicle.
The production of the M4A1 began in February 1942 at the Lima Locomotive Works, and a month later at the Pressed Steel Car Company. The production versions received many of the modifications that were requested upon the approval of the T6. The M2 gun was eliminated and replaced by the 75mm M3 gun. The side hull doors were eliminated because they created a weakness in the side-hull armor. A 2-inch thick main gun shield was added over the T48 gun mount in order to increase protection. The new mount was designated the M34 combination mount. A 1-inch thick shield was placed over the rotational ball turret bow machinegun for increased protection and both fixed bow machineguns were eliminated. Ventilation was improved with the installation of three armored ventilators, one in the middle of turret roof and two of them, on top of the hull, behind the turret. A .50 caliber machinegun was installed at the tank commander's hatch. A new assistant driver - bow gunner's hatch was installed that was a mirror copy of the driver's hatch to allow the assistant driver a means of escape from the vehicle. The 75mm gun received a new telescopic periscope gun sight for the gunner. A metal blade vane sight was also added for the commander to rough align the gun with the target. Production of the 75mm M4A1 went from February 1942 to December 1943. The welded hull M4 started production in July 1942. The cast upper hull M4A1 started production first due to the engineering and production concerns caused by the increase in the amount of welding and the number of armor plates that were required to build the welded M4 hull.
Armament: The main armament for the M4 was the same as the M3. The 75mm gun M3 was installed in the M34 gun mount. In October 1942, the gun sight for the 75mm M3 was changed from a telescopic periscope sight to a direct telescopic sight mounted in the gun mount. The periscope sight was retained as a backup. The new gun mount with the fixed sight was designated the M34A1 gun mount. The new scope significantly improved the aiming and performance of the 75mm M3 gun.
The secondary armament for the M4 was two .30 caliber machineguns and one .50 caliber machine gun. One of .30 caliber machine guns was mounted coaxially with the main gun in the turret mount and the other .30 MG was mounted in a rotational ball turret in the front hull. The .50 caliber machinegun was mounted on the tank commander's hatch ring for anti-aircraft purposes.
Armament Performance (Armor Penetration):
75mm M3 gun: Muzzle velocity: 2,030 fps(619 m/s)
Armor penetration at 30 degrees obliquity: AP M61
at 500 yds. 2.6 inches(66mm)
The M4s 75mm M3 gun had the ability to penetrate any German tank common during 1942. The German Mk. III had a maximum armor thickness of only 30mm of armor and the German Mk. IV had maximum armor thickness of 50mm. In late 1942 and early 1943 US tankers started to encounter the German Mark VI Tiger I. The 75mm M3 gun proved ineffective against this tank. The M4's only chance to penetrate the Tiger I from the front was at very close range, less than 100m. The sides and rear of the Tiger could be penetrated from farther away.
Ammunition: The M4A1 (early) and the M4 (mid) carried different amounts of ammo. The welded hull on the M4 allowed for the stowage of more 75mm ammunition than the cast hull M4A1 Sherman.
M4A1 (Early) Type Amount 75mm
90
M4 (Mid) Type Amount 75mm
97
Armor & Protection
M4A1 (Early):
Type: Turret:
Cast Homologous Steel Thickness
and Angle with Vertical: Hull Front: Actual Thickness @ 0 degrees (T/cos v) Effective Armor Upper: 2 inches (50 mm) at 37-55 degrees 63-87 mm Lower: 2 inches (50mm) at 0 to 45 degrees 50-71 mm Sides: 1.5 inches (38mm) at o to 10 degrees 38 mm Back: 1.5 inches (38mm) 38 mm Top: 0.5-0.75 inches Bottom: 0.5-1 inches
Turret: Actual Thickness Effective Armor Gun Shield: 3 inches (76mm) at 0 degrees 76 mm Rotor Shield: 2 inches (50mm) at 0 degrees 50 mm Front: 3 inches (76mm) at 30 degrees 87 mm Sides: 2 inches (50mm) at 5 degrees 50 mm Rear: 2 inches (50mm) at 0 degrees 50 mm Top:
1 inches (25mm)
25 mm M4 (Mid)
Type: Turret:
Cast homologous steel Thickness and Angle with Vertical: Hull Front: Actual Thickness @ 0 degrees (T/cos v) Effective Armor Upper: 2 inches (50 mm) at 56 degrees 89 mm Lower: 2 inches (50mm) at 0 to 45 degrees 50-71 mm Sides: 1.5 inches (38mm) at 0 to 10 degrees 38 mm Back: 1.5 inches (38mm) 38 mm Top: 0.5-0.75 inches Bottom: 0.5-1 inches
Turret: Actual Thickness Effective Armor Gun Shield .5 inches (89mm) at 0 degrees 89 mm Rotor Shield: 2 inches (50mm) at 0 degrees 50 mm Front: 3 inches (76mm) at 30 degrees 87 mm Sides: 2 inches (50mm) at 5 degrees 50 mm Rear: 2 inches (50mm) at 0 degrees 50 mm Top: 1 inches (25mm) 25 mm
Engine and Suspension:
Engine: The new M4 and M4A1 were equipped with the Continental R975 EC1 air-cooled radial engine instead of the Wright R975 EC2 that was used in the M3. The EC1 engine produced the same 400 hp as the EC2 engine. The main difference between the two engines was the reduction in compression ratio in the EC1 engine. This reduction allowed for the use of lower octane gasoline in the M4 and M4A1 compared to the EC2 equipped M3. The EC1 engine was fitted into the M4 in the same way as in the M3. The engine was separated from the fighting compartment by a bulkhead. A driveshaft extended from the motor through the bulkhead to the transmission that was located below the driver. Power was transmitted to the two front sprockets through the differential at the front of the tank. The following table shows the engine used and the max speeds for M4 and M4A1.
Tank Engine Horsepower Max. Speed M4
Continental Radial
400 hp
24 mph
Suspension: The suspension for the M4A1 and the M4 was the vertical volute spring system developed for the M2 and M3. The M4 and M4A1 received the new heavy-duty suspension bogies and rear mounted track return rollers. The new suspension bogies and rollers were designed to prevent spring failures. The ground pressure for each model is listed below (based on T48 tracks).
Tank Ground Pressure (PSI) M4
13.7
Miscellaneous Equipment: The M4 and M4A1 were supplied with many different pieces of equipment. Each tank was equipped with an SCR-508 radio that was used for communication between tanks in a platoon. The platoon commander's tank was also equipped with an SCR-506 radio that was used to communicate with HQ. The SCR-508 was located in the rear of the turret and the SCR-506 was located in the right front sponson. Some of the M4s and M4A1s might have been equipped with the SCR-528 or 538 in place of the SCR-508. The communications network allowed all crewmembers to communicate with one another during an operation. Each crewmember was equipped with a set of earphones as well as a voice microphone that plugged into the inter-phone system that was part of the radio.
Each M4 and M4A1 was also provided with 2 CO2 fire extinguishers, a 10 lb. fixed fire extinguisher and a 4 lb. portable fire extinguisher exactly the same as the M3. The crew used the fire extinguishers to extinguish non-catastrophic fires inside of the vehicle.
Each M4 was also provided with 1-M1928 .45 caliber sub machine gun and 12 hand grenades. The M4 also was equipped with a M3 smoke mortar that was fixed in the turret roof. The smoke mortar was used to quickly fire smoke grenades in order to conceal the tank from incoming direct fire. The M4A1 was not equipped with the smoke mortar.
Total Production: Tank Number Produced Production Dates M4A1 (Early)
6,281
Feb 1942 - Dec 1943 Total Production 13,029
Many of the M4s were shipped to other countries through lend-lease agreements. The chart below shows the amount of M4s that were kept by the US and the amount sent to Great Britain, the Soviet Union and other countries.
Tank
US
Great Britain
Soviet Union
Other Total
9,933
3,038
58
Early Combat in the M4: The first shipment of Shermans arrived in the Middle East on September 11, 1942. The English 8th Army immediately modified these Shermans for desert combat. On the evening of October 23, 1942, the battle of El Alamein started. The new Sherman medium tank would see its first combat the following day. On the morning of October 24, 1942, the 2nd Armored Brigade engaged elements of the 15th Panzer Division. The British M4A1s destroyed some of the opposing German Mk. IVs at a range of 2000 meters and caused the Germans to withdraw after suffering the losses. The British also lost some of their M4s in this engagement. The M4 had proven itself on par with the German long barreled (KwK 40) armed Mk. IV in its initial engagement.
The US M4's first saw combat with the 2nd Battalion, 13th Armored Regiment. All five tanks were knocked out on December 6, 1942 by well placed anti-tank guns. The initial use of the M4 by US tankers proved to be disastrous. Again on February 14-15, US tankers of the 2nd and 3rd Battalions of the 1st Armored Regiment were almost completely wiped out in an attack on Sidi Bou Zid.
This is a quote from Lieutenant Colonel Louis Hightower describing some of the action in an M4A1 Sherman around Sidi Bou Zid, in January 1943(Ralph R. Zumbro "Tank Aces" from Armored Magazine).
"We pulled out about 1700 that morning, in response to a call that 30 German tanks were attacking a hill called Djebel Lessoude, not far from the town of Faid. When we got there, 15 German Mk IV tanks were ahead of us on the eastern crest. To our left, there seemed to be 22 more German tanks. My battalion pulled up in rough line, and we began to slug it out. In the first engagement, we lost three Shermans and knocked out 5 or 6 German tanks. Then the 22 tanks came over the hill at us, which turned out to be 50 Mk IVs and at least 4 of the new Mk VIs, the awesome Tiger I. Our battalion, seriously outnumbered to begin with, we began to pull back as the Germans tried their usual trick of envelopment. They sent out a long pincer on each side of us, trying to get behind us from both sides. We kept pivoting and shooting at first one German pincer and then the other. We kept from being surrounded, but at a heavy cost. We were losing tanks, knocked out but not killed, just disabled, when their dive-bombers caught us and came in wave after wave.
They didn't hurt us much, as the TCs could see the bombs falling and have their drivers dodge them, but they smoked us up so bad that we couldn't see. I had my artillery FO call in some 105mm barrages while we pulled across 2 miles of open field in Sidi Bou Zid. The front line here was very fluid, and the town had changed hands several times. Now we'd gotten back to our artillery, self-propelled 105mm guns, and they covered us by using their guns for direct fire against the German tanks. They were now hitting Krauts with every pop, and I saw 3 Mk IVs flame up with just three shots.
We reorganized in the town, but after about 2 hours, they began another huge double envelopment, and we had to pull back again. We got our artillery and supply trains safely on the road and then started down the road back to Gafsa ourselves. After getting all our tanks under way, except for my HQ section, which we were 2 light tanks and 2 medium tanks. We took out across country, very cautiously as were outnumbered and, considering the existence of the Tigers, seriously outgunned. We meant to cover ground more quickly than a road-bound column, and it was fortunate that we had. Suddenly we heard gunfire and, coming over a rise we came upon a debacle.
Nine Mk IVs and a Tiger were shooting up one of our columns of half-track and light vehicles. The gun on the other medium tank was jammed and the 2 light tanks were too thinly armored for the task before us, I sent them away. I ordered our column of light vehicles to swing in behind us, as my driver raced to put us between them and the Germans.
As the Germans turned for what they thought would be a picnic, we let go and struck their commander's tanks with our third shot. He stopped cold as if he had hit a tree. We got a second tank with one more shot, and the German tanks braked to a halt and began to fire at us in earnest. We could fire on the move, though, and kept going at about 15 mile per hour. We put three more shots into another German tanks before discovering that it was the Tiger. I saw the shells burst against him, but I don't know if he was disabled. However, he didn't shoot at us again, so we must have done some damage.
Another Mk IV came up to him, and we got that one with one shot, still moving ourselves. He flamed up like a flower. The another Mk IV approached the Tiger and the burning tank, which was stupid because all my gunner had to do was move his sight over a hair, and that tank also flamed up with the first shot. Then our gun overheated and jammed, and we were in serious trouble as the remaining Mk IVs really opened up on us. We could actually see the shells coming along close to the ground, like a ricocheting stone on the water. One shell fragment came straight down our gun tube, rattled around the but caused no serious damage. Another shell went through the bogie wheels, under the tank. Then with a sound like a giant bell, a shell hit our turret, but didn't penetrate. Another hit made our ears ring, but we kept on working on that jammed breechblock. As soon as our gun was unjammed, we began firing again, but now a German 75mm shell smashed the bottom of our left gas tank, and blazing gasoline spurted out over the back of the tank, the tracks and the ground around us. Heavy black smoke began to roil up from our hull. I shouted to my boys, "Now is the time to git" and we boiled out like peas from a hot pod."(Zumbro: 107-110)
The M4 Sherman, after its initial losses, began to prove itself as an adequate adversary to the German Mk IV tank. Tank crews learned from their mistakes and began to develop tactics to defeat a very experienced enemy. The M4 and M4A1 would undergo many improvements to help make it more survivable and better suited to face German armor on the battlefield.
One of the many problems associated with combat in the early and mid production M4 and M4A1 Shermans was the problem of "brewing up" when penetrated by an AP round. "Brewing up" is when a tank catches fire in the interior-fighting compartment. The M4 gained a seriously bad reputation for catching fire immediately after it was hit, limiting the survivability of the crew. Initially this problem was blamed on the gasoline-powered engine because the fuel used was highly combustible. The British nicknamed the Sherman the "Ronson" after a popular brand of cigarette lighter that was advertised to light on the first try every time. What actually caused the Sherman to "brew up" most of the time was AP hits to stored ammunition. The ammunition storage on the early and mid production M4 and M4A1 was in the right and left sponsons and at the rear of the turret. Extra ammunition was also typically stacked on the turret bottom. With many different locations for the stored ammo, it was fairly easy for a penetrating round to light up some of the stored ammunition causing the entire interior of the Sherman to catch fire.
It became common practices for German gunners to target the ammo storage racks on the Sherman to completely knock it out of service. Extra armor was welded to the sides of the hull over the ammunition storage racks to offer greater protection from ammunition fires. Extra plate was also welded on the interior of the ammo boxes for the same purpose. These measures were not very successful in limiting the "brewing up" of the early and mid production M4s and M4A1s. The development of "Wet Storage" for the ammunition significantly reduced this problem. Wet storage for the Sherman was first introduced in 1943 but did not get to the battlefield until 1944.
In March 1942, the war department decided that all US operated tanks shipped overseas would be powered by gasoline fueled engines in order to homogenate the fuel supply. The US would not use diesel-powered tanks in combat during World War II. Both the M4A2 and the M4A4 were rejected for US overseas combat due to different reasons. The M4A2 was rejected because it was diesel powered and the M4A4, while not diesel powered, was rejected because its engine was overly complex. Both of these tanks would be produced and shipped to Great Britain and Russia under lend-lease agreements.
Production of the early M4A1 armed with the 75mm gun M3 ended in December 1943. A major redesign of the M4 series had started in July 1943 in order to make the M4 series of tanks more combat effective. The new M4A1(76)W would be the first of the newly redesigned tanks to roll of the assembly line in January of 1944. The next article will cover this vehicle.
References: Cooper, Belton Y., "Death Traps". Presidio Press, Novato, CA 1998. Culver, Bruce, "Sherman in Action". Squadron/Signal Publications, Carollton, TX, 1977. Hunnicutt, R.P., "Sherman: A History of the American Medium Tank". Presidio Press, Novato, CA 1994. Zaloga, Steven J., "The Sherman at War". Concord Publications, Tsuen Wan, Hong Kong, 1996. Zumbro, Ralph, "Tank Aces: Stories of America's Combat Tankers". Pocket Books, New York, NY 1997.
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