In April 1941 five proposals for a middleweight tank were brought forward to the American army. With the designation ‘Medium Tank T6’, it was obvious what is heritage was, it had the same chassis as the M2A1 and M3, and mechanics.

New was a turtle shell hull, doors at the side of the hull and a central placed one pieced turret with a 75mm cannon and a coaxial .30 machinegun. The front of the turret had a removable frontplate to accomodate other weapons than just the 75mm. As with M3 there were two .30 fixed machineguns placed in the hull (beside the one for the assistant driver).

In May 1941 the Ordnance Committee gives the order that a wooden ‘mock-up‘ and a prototype must be built. The first prototype, built at Aberdeen, had a cast hull. The second so called ‘pilot‘ was constructed bij Rock Island Arsenal. This one had a welded hull but no turret. In September 1941 the T6 was presented at Aberdeen to the Armored Forces and the Ordnance Department. It had a 75mm M2 cannon. For balance reasons some counterweights were placed at the end of the barrel. In the turret were on both sides pistolports. During the first inspection changes were made. The two sponson doors on the side of the hull were eliminated. Just as the high cupola for the commander. Later on an order was given that near the commanders cupola a .50 machingun had to be installed and that the front machinegun was placed in a ball for better movement. The name, M4 Medium Tank, was in October 1941 standardized when testing was successfull. Beside the designation in a letter/number, the name Sherman was adopted, as suggested by the Brittish army, after General William T. Sherman, who fought with the Nothern troops during the American Civil War.

By early 1942 the first new tanks came of the production line. One of the first changes was deleting the doors on the side of the hull. An extra hatch was installed for the co-driver/machinegun operator. Underneath in the floor an escape hatch was placed. Mould casting the rounded hull in one piece was not an easy task. It was very time consuming and the expected 2000 hulls in a month were to optimistic. Factories that were not equipped with mould casting facilities were given the solution to built a hull by welding. The tanks with the welded hull were designated M4 and with the moulded hulls M4A1.

De M4 series were build by eleven factories and hundreds of subcontractors.The original M4 had the same engine and chassis as the M2A1 and M3. The engine, a Wright built, Continental R-975 was from origin an air-cooled nine-cylinder radial aircraft engine. But the re-arming in the United States asked for all the aircraft engines they could lay their hands on. Testing of diesel engines for the tanks were not a great success, and were (for the time being) not built in the standard M4. But when the production got on its way, the M4 Sherman became America's most produced tank.

Despite all the different versions the basis of the M4 Sherman tank changed little. The crew consisted of five men. The driver was positioned left of the transmission. He controlled the tank with levers. To brake the vehicle he pulled both levers towards him. Beside him was the assistant-driver who had a .30 caliber machinegun in front of him. In the turret, on the right-side had the commander his place, with in front of him the gunner. In the left of the turret was the position of the loader of the cannon.

For each of the crew was a periscope built in. These where adjustable in height and could turn. Except the one for the gunner, this was fixed to the barrel of the gun, so it was always in sync with the position of firing. Early types M4 had also slits for the driver and assistant-driver. Later models had six instead of one periscope in the turret for the commander, this was a great improvement for spotting around the tank. Entrance for the crew was in front of the hull for the driver and his assistant and through the hatch of the commander in the turret. Behind the assistant-driver was an escape hatch in the floor.

As a standard the M4 was equipped with a 75mm cannon and a coaxial .30 machinegun. This whole combination had an elevation of 25 degrees up-wards and 10 degrees down-wards, adjustable with a hand wheel. The cannon had a gyrostabilizer that held the barrel targeted at one point when in movement. The cannon and coaxial machinegun where fired electronically trough a footswitch, left of the gunner. The turret could turn 360 degrees, electrical or by hand.

Besides the standard 75mm gun, there was also the 76mm cannon. The 76mm M1A1 cannon was superior to the 75mm M3 cannon, even if the caliber was only just a millimeter larger. Because of the greater velocity of the shell, the distance and penetration, the M4 equipped with the 76mm was more potent against the German panzer. It was capable to penetrate 10cm of armor over a distance of a 1000 yards (however, many German tanks escaped because the angle was not right, and the shell bounced of). The British version of the 76mm was the 17 pounder (76,2mm) in the Sherman Firefly, was a much better cannon and was more capable of penetrating German armor.

Sometimes it is difficult to find the differences in the model of the M4. The M4 and the M4A1 both had the nine cylinder radial R975 from Continental as engine. Here is, at the back of the tank, a distinctive differences with the later models. The M4 and the M4A1 had a horseshoe shaped cut out rear hull plate and a double door for the engine compartment. Central in the rear hull plate was a little hole for the hand crank to turn the engine by hand.

Because I misinterpret the hole in the rear (I thought it was for starting the engine by hand), I received a mail from Pierre de Keuster. As a former soldier of the Belgium armoured force (2 Lansiers) he knew all about the starting procedure of the Continental R 975. His words were that clear, I copied most of them below.

The hand crank was not for starting the engine. With radial engines with a dry crank-case the possibility occurred that after shutdown of the engine, the round swept oil, was not only dropping in the 5th cylinder, but also between the piston and the cylinder and filling the combusting chamber. When both valves were closed of the 5th cylinder, and the compression was started, and the volume of the oil was bigger then the space of the combusting chamber, then there was a problem. A fluid can not be pressed, and a hydrostatic block was created. When the driver had such a situation and should start the engine with booster and the next cylinder would ignite, then the engine would fail and the crankshaft damaged.

The normal sequence after a long period of rest was:
- The driver does his normal checks.
- Sticks the hand crank in the hole at the rear and turns it 50 times (that is one turn-over of the engine), to check if the engine is neutral.
- When the engine is blocked: remove the sparkplugs, drain the oil from the cylinder, replace the sparkplug, and start the engine.

With the introduction of the M4A2 and her General Motors 6046 diesel engine and the M4A3 with the Ford GAA V-8 engine, the rear of the M4 changed, it became a straight rear plate, to protect the vulnerable rear.

During the development of the M4, it was also considered to use this medium tank for the 105mm howitzer. When the M4 went into production, the development started for the 105mm. Designated as the T70, two pilots where built and delivered by the Detroit Arsenal in November 1942. The test vehicles were M4A4 tanks equipped with the 105mm howitzers M2A1 and were designated as M4A4E1 by the Ordnance Committee.

First testing started on December 7, 1942 at the Aberdeen Proving Ground with serial number: 5868, W-3057678. The other pilot, W-3057717, was sent to the Armored Board, Fort Knox for testing. During testing it was discovered that the loader had to reach above and over the gun to handle the breech. Also the continuous-pull type trigger was not ideal. The counterrecoil buffering was evenso insufficiënt. The turret was also not in good balance. When 30 degrees was climbed, the electric power unit, that traversed the turret, would not work properly.

After al was fixed, the electric power unit for the turret was made manual, the breech of the gun was redesigned, and the pull fire equipment was replaced for a trip-off firing mechanism, the testing was continued in August 1943. The two new pilots were designated M4E5 and had M4 welded hulls. The 105mm howitzer was type T8, it was lighter in weight and easy to work with, in the little turret (it was later standardized to 105mm howitzer M4). Meanwhile the storage of 105mm ammunition was increased to 68 rounds (was 58). Fourtyfive were placed in floorracks, twentyone in the right sponson and two in the ready rack. The Armored Board gave the go ahead after they wanted more ventilation through an extra fan in the turret. There were more modifications needed, but the 105mm was demanded in the field, so the production was started.

Different types of ammunition was available for the howitzer, but onboard were 42 high explosive M1 grenades. It was not easy to hit a target with the howitzer because of the curved trajectory. But when a hollow charge of a high explosive anti-tank (HEAT) M67 hit the target (with a maximum of 2.5 inches/100mm) the effect was impressive.

The first production of the M4 105mm resembled the hull of the M4A3 with the steep front plate, but this was a rebuilt M4 with the Continental R975 engine. A total of 1641 were built of the M4 105mm before the production stopped in Februari, 1945. Most of the M4 105mm were produced with the split flat hatch for the commander and an oval hatch for the loader. Later models were given the cupola with the muliple periscopes.

With the introduction of the M4A3 hull and the 8 cylinder V-Ford GAA engine it came also available for the 105mm. Production started in May 1944 and 500 were produced until September with the vertical bogie. After September only the M4A3 with the HVSS (2539) were built before the production stopped in June 1945. On starboard side of the gun shield was a large hole for the direct vision telescope. This was a vulnerable place for small arms fire. This was made smaller and was given a moveable shield to cover it.

From the battlefield complains were coming back, such as concerning the missing of a power unit to traverse the turret. The last 105mm tanks coming from the production line were equipped with a new power unit, but came too late, as the war had ended. Another problem was the enormous noise the engines of the M4 and M4A3 produced. The enemy could locate the tanks by listening at the noise that was coming towards them. Often a artillery barrage was given (or low flying airplanes used) to conceal the approach of these Sherman tanks. A better muffler system was made and installed in the last production but these also reached the fighting forces too late as the war was ended.