between −3° and +26° and had 10° of traverse. The five-man crew consisted of a driver, gunner, commander and two loaders. By 25 November 1942, the first U-35 prototype was ready. Trials ran from 30 November to 19 December 1942, and uncovered various faults in the design, including insufficient elevation, a flawed shell transfer mechanism, poor ventilation for the crew compartment, and the fact that the commander had to assist in operating the gun, which made him unable to successfully carry out his other duties. The U-35 entered service with the Red Army as the SU-35 (later renamed SU-122) despite these faults. Production SU-122s were based on an improved prototype built after trials were conducted. They incorporated several modifications, including slightly less sloped front armor to ease production, modified layout of the fighting compartment (the location of crew member stations and ammunition racks were changed), fewer vision slots, and a periscope for the commander. The first production vehicles were completed before 1943. Production history SU-122 production began in December 1942 with 27 vehicles built that month. The original plan for production beyond that point was to produce 100 SU-122s each month. Production continued until the summer of 1943, by which time a total of 638 SU-122s had been built. Service history The first SU-122s produced in December 1942 were sent to training centers and two new combat units, the 1433rd and 1434th self-propelled artillery regiments. Initially, each of these mixed regiments consisted of two batteries with four SU-122s each and four batteries with four SU-76 tank destroyers each. Each regiment had an added SU-76 tank destroyer as a command vehicle. It was planned to raise 30 self-propelled artillery regiments operating within armoured and mechanized corps. In January 1943, the 1433rd and 1434th self-propelled artillery regiments were sent to the Volkhov Front near Leningrad as part of the 54th Army. On 14 January, they saw combat for the first time in Smierdny region. After that, it was decided SU-122s should follow between 400 m and 600 m behind the attacking tanks; sometimes this distance was shortened to between 200 m and 300 m. The use of SU-76 tank destroyers together with SU-122s proved unsuccessful. Based on combat experience, the organization of self-propelled artillery regiments was changed; the new regimental organization consisted of two batteries of SU-76 tank destroyers and three batteries of SU-122s, for a total of 20 self-propelled guns. In