One has to bear in mind the extremely rapid technical development of tanks in the 1930s, especially the latter half of the decade, in combination with doctrinal confusion in most armies.

With a large weapons budget the Soviets tried out a bit of everything: very light and amphibious tanks, armoured cars, 'infantry' tanks and 'cavalry' tanks, and multi-turretted heavies.

I'll put aside the very light tanks (the Wehrmacht recognised these as suitable only for training, though they were of course forced to use them in combat for several years) and the heavies (which the Wehrmacht barely pursued due to resources issues and the need to focus efforts on building up a core of mediums).

The basis of Soviet armoured power were their T-26 and BT-5/7 series. Although both would have been experienced by the Germans at Kama, the T-26 was simply a local version of the Vickers '6-ton', the derivatives of which equipped many armies including those of Poland, Rumania and Italy. The BT was of course the only real export success for the American, Walter Christie. So both tanks would have looked fairly derivative to observing Germans.

In 1933 Soviet military power generally was fledgling. Kama was a mutually convenient operation because both nations were military pariahs. German armoured development was yet to start in earnest, and the Soviets were a long way from the massive factories and fleets of 1939.

To return to technical development, it is here that we can see the nations that had the best tanks in 1941 were those that made a few good decisions half a decade earlier. The key Soviet decisions were to develop a lightweight tank engine of massive power, a 500hp V-12 diesel. Germany with her proud automotive traditions and Nazi militarism were also able to develop decent petrol engines through Maybach, but Western nations mostly had to blunder along with converted truck engines or over-worked motors. The issue was tanks really needed their own engines with had limited commercial application, so non-militarist/fascist powers were at a disadvantage. The 500hp V2 engine gave the T-34 great speed and the KV-1 decent performance, at a time when most 'heavy' tanks could only manage walking pace.

The other key Soviet decision was to base their medium on the BT and Christie's greatest achievement, his long-travel suspension. Even in just the early 1930 tank suspension was a huge technical problem: a system that was strong, but offered any wheel travel, was hard to design (one reason for the success of the Vickers 6-ton was its suspension, which was still very crude). Tracks had only a short life and couldn't manage much speed. The Soviets solved these issues in part by over-engineering at a time other rival powers were held back.

The invasion of Poland and Germany's success was a wake-up call for Stalin, and his armed forces- extremely modern in 1935- were becoming obsolete. Secrecy and the purges distracted Germany and other powers. Many designers had to work from prisons. And indeed there were huge technical struggles, but several key Soviet weapons were just coming into service in 1941, and it was this newness, as much as anything, that prevented the Germans gaining a realistic appraisal of Soviet power- had they even wanted to do so once bent on invasion.

Among the weapons that were to play a key part in the war which were just entering service were the T-34 and Kv-1, the MiG-3, Yak-1 and LaGG-3 fighters, and IL-2 ground attack plane, as well as various classes of field and anti-tank artillery.