I send you these materials on trials of fighting and armoured vehicles BT-7A, T-38, FAI and trucks GAZ-AA, ZiS-5, ZiS-6 regarding their performance during border and internal maneuvers executed by the NKVD Internal Forces in 1937-1938.
Experience in using these vehicles in conditions of middle Asia revealed several design defects that must be corrected when building these vehicles.
I ask you to inform me of your decision.
Division commander Kovalev
Of trials of BT-7A, T-38, FAI armoured car, GAZ-AA, ZiS-5, and ZiS-6 trucks.
Trials were performed in the following conditions:
- Total distance: 2500 km (without assistance, combined on tracks and wheels)
- Terrain: various
- Mountains with steep grades, mountain passes at an elevation of 2500 m to 4000 m, mostly off-road, up to 1000 km long.
- Rocky bed of a mountain river, 200 km.
- Off-road on a salt marsh, 250 km.
- Dirt roads with up to 50 cm of loess dust, 100 km.
- Loose sand, from flat sand roads to loose dunes with grades up to 40 degrees, up to 1000 km long.
- Climate conditions:
- Mountains with a normal temperature of +15, salt marshes with a temperature of +50, mostly through regions without water.
- Sand-salt marsh terrain with air temperature ranging from +10-15 degrees to -15 degrees.
- Mountain passes up to 4000 m high in winter conditions with snow banks with temperature ranging from -20 to -40.
- Requires dust protection with a more powerful oil filter, better sealing of the carburettor and coil pipe housing.
- The fuel nozzles should be moved in order to avoid a chance of fire if gasoline leaks on the magneto contacts.
- The valve rocker leaks oil during use and cannot be repaired.
- The gear-based oil pump and its connector wear quickly.
- The nozzles cannot be regulated without removing the top armour plate.
- It is difficult to access the engine during use.
- The main friction clutch must be protected by a special case (from the engine to the gearbox)
- There must be an intermediate connector between the main clutch and gearbox that allows for work on the clutch without removing the gearbox.
- Strengthen the bearings of the main friction clutch and improve access to them and the ratchet disk.
- Improve access to the oil nozzle of the final drive bearings.
- Cover the control pull rods with a special casing.
- Improve the gearbox link (springs break, locks pop out, other breakdowns).
- Install strengthened ball bearings.
- Redesign the drive wheel in order to strengthen the disk and rim.
- Change the tracks to use finer links.
- The lights turned off due to poor quality of lightbulb sockets.
- Up to 80% of ammeter and voltmeter breakdowns were due to poor quality of materials or assembly.
- Starters broke down due to poor quality of relay contacts.
- Bronze bearings of the launch magneto wore quickly.
- The generator plug connectors are unreliable and hard to reach.
- The electric equipment layout is complicated and hard to reach during repairs.
- The ignition button contact (made from a latten brass spring) is low quality and breaks quickly.
- Electric wiring close to the turret creates a fire hazard.
- Protect the magneto, generator, and starter from dust and moisture. The started magneto should be installed on ball bearings.
- Remove the plug connectors from the generator and lead the wires up to the control panel near the generator.
- Allow access to the starter relay without removing the starter.
- Note: a Bendix gear starter is desirable. In addition, the tank should have another way of starting the engine aside from the starter.
- Wiring inside the tank should be done in accordance with fire safety. Wires in the turret should be covered in pipes until they reach their contact.
- Small connectors should not have friction contacts, and should be connected with either bolts or solder.
- The battery should be moved to the rear of the tank, as during operation water, oil, and dust gets on it, and leaking electrolyte corrodes the radiator.
- T-38 tank: demonstrated excellent performance in all conditions, aside from:
- Fast wear of final drive gears.
- Insufficient engine power for the vehicle's weight, causing overheating, and low speed on land and water.
- It is necessary to add air filters to the engine.
- FAI armoured car: showed good results. It is necessary to add an air filter and improved radiator.
- GAZ-AA: showed good performance and endurance. Needs an oil air filter and an improved radiator.
- ZiS-5: performs poorly on sand. The reductor is very weak, mostly the gears and bearings of the main gear break. Needs a stronger radiator and a rigidly installed differential like on the GAZ truck.
- ZiS-6 (three-axle): needs a more powerful engine. The existing engine can only provide a speed of 12 kph on the described terrain. The demultiplexor is very weak, the gears of the first gear break often. Needs a stronger radiator.