The 1930s saw the Soviet military start to take a mature approach regarding mechanization, but it was industrially far behind, especially considering their large army. Mass production of simple trucks such as the ZiS-5 and GAZ-AA was not enough, and a heavier truck was needed. One of these was the YaG-12, essentially a YaG-10 truck with 8×8 wheel drive. A single prototype was built, tested, and shown at the October Revolution parade in 1932. Although a capable machine, the factory’s low production capabilities, the truck’s high price and the maintenance cost, as well as the military’s desperate need of simpler trucks, cut the project short.
In the late 1920s, as the Soviet Army was beginning its tedious process of troop mechanization, a crucial element needing desperate attention was trucks. Up until this point, the main Soviet truck in military use was the AMO-F-15, a license-produced Fiat F-15, which itself was launched in 1911. Consequently, most of the logistical and transport duties of the massive Soviet Army were done by horses. The solution was to begin mass production of trucks across several factories, with the help of Western patents and factory toolings. As a result, two of the most famous Soviet trucks of the Second World War were born, the GAZ-AA and ZiS-5. However, both of these trucks were light, around 2 and 3 tonnes respectively, and a larger truck was needed. Thus, Plant No.3 Yaroslavl State Automobile Plant (YaGAZ) was tasked with production of the Ya-5, a 4.8 tonne truck, an improved variant of the Ya-4 using an American engine. The YaGAZ plant had previous experience with heavy trucks, starting with the Ya-3, but only 160 units had been built.
By 1931, YaGAZ was tasked with producing a new 3-axle heavy truck to better cope with the needs of the military. This would become the YaG-10, which kept much of the same features as the previous trucks, but had an extra axle and longer flatbed, thus the weight increased to 6.8 tonnes and load capacity to 8 tonnes. The rear bogie housing the two rear axles was a copy of the British WD type, while the engine was an American Hercules YXC outputting 96 hp.
By 1932, the YaG-10 was to enter production with 100 units built per year. However, a multitude of issues prevented this, and by 1940, when production ceased, only 333 units had been built.
Shortly after the YaG-10 entered production, YaGAZ was tasked by the Scientific and Technical Committee of the GABTU (Main Directorate of Armored Forces) with developing an even larger and heavier truck, not just for increasing the maximum payload capacity, but more importantly, to increase the cross-country capabilities of the truck. This was a very important element in the Soviet Union at the time, as it was a country which lacked an infrastructure network for which not even 3-axle trucks were often adequate. Furthermore, towing heavy artillery systems proved to be a great challenge as well, and the need for a larger truck with good off-road capabilities became clear.
The larger truck was to be an 8×8 vehicle, largely inspired by what Soviet dellegations saw in international exhibitions, especially regarding the British AEC Mammoth and Guy 8×8 artillery tractor. After failed attempts to purchase or license-produce these trucks, the Soviets figured that they would have to create their own design; and quickly. During the same period, the Armstrong-Siddeley Pavesi P4 articulated 8×8 vehicle and AEC Roadtrain were already in development, and the Soviet Union needed their own counterpart for geopolitical reasons.
Development of the new truck began at YaGAZ with the chief designer being A.S. Litvinov, head of the plant’s design bureau. Heavily involved in the project was also the director of the plant, V.A. Yelenin, and engineer V.V. Osepchugov. Their task was extraordinary, as the plant lacked the skill and experience in such complex systems, their entire truck lineup having been essentially just made by tinkering with the engines of the same chassis. The new truck was to be named YaG-12, not to be confused with the Ya-12 tracked artillery tractor, produced between 1943 and 1946, also in Yaroslavl.
The drawings were ready by summer 1932 and manufacturing began in September. By November, the YaG-12 was ready. This hasty schedule was partly due to Yelenin’s promise to the military of delivering the truck for the 15th October Revolution anniversary, which actually took place on 7 November according to the Gregorian calendar. The entire plant was working towards this goal. In the last 3 days, there were 3 shifts a day, while the engineers and directors were working constantly. On 5 November, at 23:00, the engine was started for the first time, and the last checks were made. At 23:30, the truck left the shop. At its wheel was the head of the YaGAZ production department, M.K. Mroz, and next to him was Litvinov. After a speech and meeting, the YaG-12 was accompanied by several YaG-10, all headed for Moscow.
The basis for the YaG-12 was the 3-axle YaG-10 truck. Many components were recycled, from the cabin and engine cover to wheels. The truck maintained a standard layout, with the engine in the front, central cabin, and flatbed in the rear. Compared to the YaG-10, the flatbed was shorter, due to the additional space needed for the wheels and drive mechanisms.
The main external change was the addition of a second bogie in the front of the truck, with two wheels per side. To accommodate this, the fender was enlarged, running across the entirety of the hood and most of the cabin. While most of the truck was made out of thin sheet metal, the flatbed was wooden and the cabin had wooden elements. The rear bogie remained virtually unchanged from the YaG-10, with four wheels with two sets of tires each. The tires were standard 40×8 inch ones, which were not great for off-road use, but the truck having 12 of them increased its performance. There was a tire inflation compressor, but no deflation system. The front wheels had just one tire to facilitate easier steering, considering that the steering was mechanical. A spare tire was located underneath the flatbed, above the transfer case. A trailer hitch was mounted at the end of the chassis frame, and a hook at the front. A winch was also mounted in the center of the frame, allowing for the cable to be used both in the front and rear of the vehicle.
Engine and Propulsion
The YaG-10 had a Hercules YXC 96 hp engine, but it was deemed underpowered for the new truck. Instead, due to the Soviet inexperience in engine design and manufacture, a Continental-22R engine was used, with a straight-six configuration, outputting 120 hp and with an internal volume of 8600 cm3. Cylinder diameter was 114.3 mm with a stroke of 139.4 mm and a compression ratio of 4.6. This engine allowed the 8 tonne truck to reach a top speed of 45 km/h and a minimum fuel economy of 52 l/100 km. An 164 liter fuel tank was placed underneath the cabin crew’s bench. The vacuum booster was borrowed from the YaG-10 as well.
The most complex part of the truck was the power transfer system, a complete novelty for the Soviet auto industry. The dry-clutch and four-speed and one reverse (other sources claim 8 forward+2 reverse) manual Brown-Lipe-554 gearbox was reused from the YaG-10. A specially designed transfer case powered all four axles through individual drive shafts.
Due to the lack of machining abilities of the factory to produce helical gears, the YaG-12 used spur gears in its mechanical components instead. While these gears are easier and cheaper to manufacture, they are far less durable and are much louder, which allegedly made the YaG-12 have an unique “howling” sound when driving. For similar reasons, no tapered roller bearings were used, or any differentials on the central driveshafts.
Before the system was assembled on the truck, a special unit was made for testing purposes. While the system worked reliably, it was noted to be rather heavy. In total, 9 drive shafts, 18 universal joints, 30 ball and 12 roller bearings were used on the power transmission system.
Suspension and Bogies
While the rear bogie remained mostly identical to that of the YaG-10, the front was completely redesigned. A second bogie was added, with both front axles being able to traverse for better steering. The steering was done via a worm gear and two longitudinal steering rods, one per axle. Each bogie was hinged to the frame in the center and sprung with 2 leaf springs, allowing for dependent movement of each axle. As one axle went up, the other went down. Furthermore, the axles were sprung to each other with a second leaf spring to smoothen out the potential jerkiness of the bogie mount. Drum brakes were mounted only to the wheels on the rear bogies, with 100 mm pads and 460 mm inner drum diameter. The hand brake was a band type and was in the transfer case, acting on all four drive shafts. A so-called mountain brake was added as well to prevent brake failure at steep angles. It was hinged to the rear hitch, from where it could be stuck into the ground.
This suspension layout would offer excellent cross-country performance across various types of terrain, allowing for all wheels of a bogie to have contact with the ground, increasing load dispersion and improving traction.
Trials and Fate
By 19:30 on 6 November 1932, the YaG-12 truck completed its approximately 250 km trip to Moscow and participated in the parade the next day. It made quite the sensation, and was the subject of propagandistic newspaper articles, showing how the USSR managed not just to catch up, but also surpass British designs in such a short period of time. After the parade, the truck was sent to the NATI proving grounds, where it was tested over various terrains and obstacles. The YaG-12 could climb 30º slopes, cross 1.5 m wide trenches, and climb over a 40 cm obstacle. It crossed 60 cm deep water and drove through 50 cm deep snow. Ground clearance was 32 cm. Load tests were made to ensure that the truck could support 12 tonnes on roads and 8 tonnes on soft terrain. A special metal and rubber track, first used on the YaG-10, was mounted over the wheels of the last bogie, further improving traction.
Naturally, several small improvements had to be made, but the experiment proved to be a success, and the GABTU originally requested 7 more trucks to be built during 1933. However, after the YaG-12 was moved over to a military unit in Saratov for further testing, all traces were lost.
The truck indeed had incredible potential, at least on paper, for both the Soviet military, but also for various civilian applications. Its excellent carrying capacity combined with superior off-road capabilities would have made it an excellent vehicle for carrying heavy artillery weapons and munitions, as a gun platform and much more. Even for civilian applications, such as dump trucks, it would have found success. However, the realities of the Soviet industry put an end to this otherwise capable vehicle. The Soviet Union as a whole desperately needed trucks, of any kind, and slowing down the YaGAZ production line even more was not an option. The truck was also expensive and mechanically complex, two features which the Soviet Army and military industrial complex could not support at the time. Alas, even with the production of trucks such as the ZiS-5 and GAZ-AA, the Soviet Union struggled to keep up with truck demand, the situation peaking during the war, when the Soviets had to rely more on Lend-Lease trucks from the USA. As for the YaG-12 designers, both chief designer A.S. Litvinov and factory director V.A. Yelenin were killed during the Great Purge, in 1939 and 1938, respectively.
Just a year later, in 1934, the Department of Armored Vehicles of the Military Academy of Mechanization and Motorization built a prototype of an 8×8 vehicle, though the janky homemade vehicle was more of an educational experiment, rather than anything meant for mass-production. Work on 8×8 trucks would only resume in the 1950s, with the EATE-1 8×8 truck, followed by several others. The first 8×8 trucks to enter military service with the Soviet Union were the ZiL-135 and MAZ-535, nearly two decades after the YaG-12.
As for the YaGAZ plant, work on improving and producing heavy trucks continued, at a slow pace. During the Second World War, the plant produced and assembled components for other factories, as well as assembling the Ya-12 tracked artillery tractor. Towards the end of the war, the plant resumed development and production of its own truck designs for both military and civilian purposes, preparing for peacetime production, one such truck being the YaAZ-200.
Despite YaGAZ’s best efforts to provide a capable machine and regardless of the truck’s performance, the project was a dead end. The factory had a very small production output of much simpler Ya-4 and YaG-10 trucks, which were desperately needed by both military and civilian users. The truck’s high price also meant that the military could not afford as many as it needed, especially in terms of maintenance. But the YaG-12 also sought to push the limits of Soviet truck design, and successfully managed to do so. For an industry limited to engine swaps and license production, this 8×8 vehicle created in such a short period of time was truly an impressive feat, and amongst the first 8×8 trucks in the world.
|Dimensions (L-W-H)||6.584 x 2.39 x 2.77 m|
|Total weight||8 tonnes, 20 tonnes fully-loaded|
|Crew||6 (commander, main gunner, main loader, secondary gunner, secondary loader & driver)|
|Propulsion||Continental-22R inline 6 cylinder 120 hp|
|Fuel tank & consumption||164 liters
52 l/100 km
|Payload (tonnes)||12 t on roads, 8 t off-road|
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