LAYOUT AND ARMOUR

The SU-76M consisted of a fixed casemate on top of a chassis made from T 70B lighttank components. The hull was split into four compartments: the driver’s compartment in the front, the transmission and engine compartments to his right, and the fighting compartment in the rear. The fighting compartment contained the 76mm ZIS-3 gun, three crewmen and ammunition. If necessary, crewmen could move between the driver’s compartment and the fighting compartment through a hatch below the gun.

The armour of the SU-76M was light, offering protection from small arms and heavy machine guns. The upper front plate was 25mm thick, angled at 60 degrees. A cut-out was made in the centre of the plate for a driver’s hatch. The curved hatch door, also 25mm thick, had an opening on the top side for a rotating periscope. A portion of the upper front plate could be removed to access the transmission. The lower front plate was 30mm thick, angled at 30 degrees. It contained an opening for the crank starter, protected by an armoured panel when not in use. The floor and roof of the hull were 7mm thick and completely horizontal, with the exception of a small portion of the front floor sloped at 9 degrees. The roof was made in sections and could be removed to service the engine. The sides of the hull were 15mm thick and vertical. The hull rear consisted of two 15mm thick plates, the top one being vertical and the lower one sloped at 30 degrees. A door was cut into the rear plate for the crew to enter and exit the fighting compartment. Air from 30 the engine compartment exited the vehicle through a grille on the right side.

The casemate protected the gun crew from the front and sides. The frontal armour was 25mm thick, sloped at 25 degrees. The sides of the casemate were 10mm thick, sloped at 20 degrees. An opening for the ZIS-3 gun was cut into the middle, shifted left of the vehicle’s centre. Pistol ports were cut into the sides of the casemate, covered by armoured shutters when not in use, and there was a vision port on the left side. An opening for a radio antenna, protected by an armoured cup, was cut into the right side.

WEAPONS

The main weapon of the SU-76M was the 76mm ZIS-3 gun. It was largely identical to the towed divisional gun, but the lower mount and gun trails were removed. Instead, the gun was installed on a beam running across the fighting compartment. This gun mount allowed for -5 degrees of depression, +15 degrees of elevation, and 15 degrees of traverse to either side. A total of 60 rounds of ammunition were carried for this gun: seven on the right side in the back of the fighting compartment stored vertically, 29 to the left of the gun stored horizontally, 17 on the left side in the back stored vertically and seven more on the right side of the gun. Auxiliary armament consisted of a 7.62mm DT machine gun, which could be fired out of the vehicle’s pistol ports; 15 63 round magazines were carried for the DT, for a total of 945 rounds. The DT was stowed on the left side of the fighting compartment when not in use. The crew also had a 7.62mm PPSh-41 submachine gun with six 71-round drum magazines (426 rounds) and ten F-1 anti-personnel grenades for close defence. The PPSh-41 was stowed on the right side of the fighting  compartment when not in use and the grenades were stored under the bench that the gunner and loader sat on during travel.

CREW

The driver of the SU-76M sat alone in the driver’s compartment in the front of the vehicle. He was flanked by the engine and transmission compartment to his right and the fuel tanks to his left. His hatch door could be opened while driving for better visibility, but he could only look through a rotating MK-4 periscope when it was closed. He could communicate with the commander by means of a TPU-3F intercom or a system of indicator lights.

Members of the gun crew, consisting of the commander, gunner and loader, were located in the fighting compartment in the rear. The commander sat to the right of the gun. He observed the battlefield through a MK-4 periscope and also had a separate TR-4 periscope for fire correction. He could use a direct-vision slit, protected by bulletproof glass and an armoured shutter, to observe the terrain directly in front of his vehicle. In addition to commanding the vehicle, he operated a 12RT-3 or 9RS radio installed in the fighting compartment to his right.

In battle, the gunner stood to the left of the gun or sat on a folding seat. He used a PG-1M Goerz-type panoramic sight with a 4× magnification and 10.5-degree field of view to aim the gun and a foot pedal to fire.

MOBILITY

The SU-76M was powered by a GAZ-203 power plant, consisting of two GAZ-70 petrol engines, producing a total of 140PS. Two fuel tanks holding a total of 412 litres of petrol gave the vehicle a cruising range of up to 320km. Top speed was 43km/h, but it was governed to 30km/h. At a mass of only 10.6 tonnes, giving a power-to-weight ratio of 13.3PS/tonne, the vehicle was quite agile, with an average speed of 34.1km/h on the highway (if a governor was not used) and 21.5km/h offroad. A gearbox from the ZIS-5 truck was used, giving four speeds forward and one reverse.

Each of the SU-76M’s tracks was composed of 72 identical metallic track links,
300mm wide. Six road wheels with rubber tyres and three all-metal return rollers guided the track. Each road wheel had its own suspension arm and torsion bar. The idler in the rear was identical to the road wheels and its position could be adjusted to control track tension. The running gear and suspension elements were common with the T-70B light tank.

You can read more in Hetzer vs SU-76M.