Welded hull. Late models had improved cupola, a loaders hatch, and wet stowage for ammunition. Had the GAA-III V-WC motor.
The original armament of the M4A3 series was the M3 75 mm gun. To be able to mount the gun in the turret it was turned on its side. Loading was on the right side.
The M34 gun mount was used early on but as it only protected the main armament soldiers in the field requested it protect the coaxial machine gun. The M34A1 was developed as a result and was standardized in October 1942. This shield was full width and had a direct sighting telescope installed.
The turret was a cast one piece design with a bulge in the rear to allow for the installation of radio equipment. The hatch for the commander could be rotated and there was a mount for a .50 cal HB AA machine gun. There was a rotating periscope for the commander in the turret hatch. The loader had rotating periscope in the roof of the turret. The gunner had a telescopic periscope that was synchronized in azimuth and elevation with the main armament. The roof of the turret also contained a 2" smoke mortar.
There was a pistol port in the side of the turret that could be used for ejecting or reloading shells.
There was a recessed ball race for the turret to revolve in that helped protect it from bullet splash.
The turret basket was bolted to the turret casting and rotated with the turret.
Later in production an armored cupola with six vision blocks replaced the rotating hatch. A mount for the .50 cal Browning AA MG was placed next to the cupola.
The hull was welded armor plate. At the expense of a desirable design it was easy and quick to manufacture.
There were two hatches in the top of the hull, one for the driver and the other for the co-driver. Behind the co-driver's seat was an escape hatch.
During production a change was made in the hull front. The full front was replaced with a 47° flat plate. This simplified production and allowed for larger hatches for the front crew. This plate also increased protection in the front. A gun barrel lock was installed in this plate.
Later in production a sand shield was installed that covered the top run of the track.
The driver was on the left side and the co-driver on the right. The co-driver also operated the hull machine gun. The could see out vision blocks that were in the hull front of early models with hatch periscopes replacing them to simplify production.
The main gun loader was on the left and the gunner on the right. The commander was behind the gunner.
The Ford V-8 engine was liquid cooled and placed in the rear of the hull. The twin exhausts went out under the vertical hull backplate. The cylinder block and crankcase were integrally cast in aluminum, but the cylinders were sleeved in steel. There were two four cylinder magnetos mounted at the rear of the engine on a cross shaft. The water pump was driven from the end of the crankshaft.
The four mounting points for the engine were rubber padded. Two of these were on the bulkhead of the engine compartment and the others in the floor.
There was a door in the rear and flaps with grilles on the top of the hull. The radiator was placed behind the engine.
There were two vertical and two horizontal fuel tanks flanking the engine. They could carry 168 gallons and could be drained out the bottom of the hull if needed. On each side of the hull top were two caps for fueling the tanks.
The driver could remotely operated two fire extinguishers in the hull compartment. These could also be operated externally.
There were five forward and one reverse gear and a built in parking brake.
Steering and stopping was done by the controlled differential which transmitted engine power to the drive unit that was at the front of the tank. The drive unit took power to the sprockets through a set of reduction gears. The power unit could be completely removed for easier maintenance.
One of the most requested upgrades from the field was an improvement to the ammunition storage. A direct hit to the ammunition storage would often lead to fire. A system that would have jackets of ethylene glycol (later replaced by water) surround the stowage and when pierced would reduce fire and the chance of explosions.
This system required an additional 2,500 design changes of the M4.