Churchill III tank at the NIIBT proving grounds, September 1942. Retrieved from Baryatinskiy, Lend Lease Tanks in Battle.
The Churchill (frequently referred to as "Mk IV" in Soviet documents) was among the various tanks received by the Soviet Union through the Lend-Lease program. As with all tanks, they put it through trials, and, as with all tanks, it had some shortcomings.
CAMD RF 38-11355-938
"List of defects discovered in the process of using the Churchill tank.
- The track link pins on the new tracks are contained with welds. This makes it difficult to repair tracks in field conditions. After replacing track pins, it is difficult to weld the covers back in place.
- Lightened tracks collect dirt and bulge out, which in turn pushes up the mudguards and make turning the turret difficult.
- Road wheels are poorly held on their axles. There were cases where they would come off and get lost during the tank's movement.
- The track link mortise is of poor quality, and is destroyed during movement.
- The main clutch gear axles are of poor quality, and sometimes break at their base.
- Rollers in the gear box are of poor quality and break.
- Gears in the gear box are of poor quality and break.
- Oil leaks from the gear box.
- The hoses from the "Amal" gasoline pump are not sturdy enough, and can tear during movement.
- The manual turret rotation mechanism is insufficiently reliable. The chain breaks, and the switch from manual to automatic traverse bends.
- The height of the driver and assistant driver observation devices does not let them see to the sides.
- The open engine grille does not prevent gasoline from incendiary bottles from getting into the engine compartment.
- Track links do not make good contact with the ground. The poor traction severely limits the tank's ability to go up and down inclines and tilt.
- Upon tilting 20 degrees, tracks fall off.
- The recoil springs of the 57 mm gun are poorly fixed, which leads to imbalances and jamming when they hit the cylinders."
In real combat, the Churchill showed another deficiency. The heaters were weak, and often replaced with domestic ones.
That's quite a list. The Soviets weren't the only ones to dislike the Churchill, however:
"The reason that the Vickers company did not receive the contract to develop the Churchill is that when the head engineer of the company (responsible for the successful Valentine tank) saw the A22 project, he refused to have anything to do with it."
The opinion of the Churchill wasn't entirely negative. A report titled "Report on short trials of the English heavy tank MkIV Churchill on the Red Army NIIBT proving grounds" from September 16th, 1942, has the following to say about the Churchill:
"The MkIV tank has weaker armament than the KV-1 and KV-1S, but superior armour. The MkIV carries three times as much ammunition for its machine guns as the KV. The AP shell from the 57 mm gun penetrates all the way through a PzIII tank from the side, 60 mm of armour in total, at 950 meters. The MkIV has lower hp/ton, and therefore a lower maximum speed, than the KV-1 and KV-1S, but its average speed is equal. The MkIV and KV are equivalent in their operational range.
The English MkIV heavy tank is insufficiently reliable, and appears to be an unfinished vehicle, both from a design and construction standpoint.
The tracks create poor visibility for the driver and hull gunner. Periscopes do not improve this situation.
The gun length, when pointed forward, does not exceed the length of the mudguards. When the gun is fired in this position, the mudguards are bent and torn off.
The observation devices installed in the turret are satisfactory.
The engine is a modern design, and uses a small amount of metals in deficit, and is thus well suited for mass production. However, the engine is unfinished, and its reliability during use is questionable.
The transmission of the tank exists in one unit with the turning mechanism. The turning mechanism allows the tank to rotate in place, and to turn the tank easily, providing very good maneuverability for a heavy tank.
The suspension is not sturdy enough for a 40 ton tank. During the short trials, inner road wheels fly off the bogey axles, followed by outer road wheels, the bogey balancers start to rub against the tracks, and break quickly. The road wheel rims make contact with the tracks in such a way that both the tracks and wheels wear out quickly. This also leads to the road wheels heating up significantly during motion. The track pins are of poor quality and break."
Conclusion: the armour and armament of the English heavy tank MkIV Churchill is sufficient to fight any German tank. The MkIV is unrefined, both from a design and production standpoint. When used in the field, it will require frequent repairs, and replacement of parts and entire modules.
Several components of the tank (turning mechanism and transmission in one block, as well as others) are very original, and can be recommended for use on domestic tanks."