Hi! This is my first time posting in this subreddit, and I hope that this question doesn't break the rule on "example seeking" questions, since this is a topic that I'm a genuinely interested in.
The wartime innovations made by the Western Allies and the Germans are well known and commonly discussed in popular literature: the radar, digital computing, assault rifles, jet fighters, guided munitions, synthetic rubber and fuels, infrared imaging, various magnetic/acoustic mines and torpedoes, and of course, the atomic bomb. Even some of the more outlandish "paper" projects, such as the Ho 229 bomber and the bat bomb, seem to be a fixture of modern discussions on WWII technology.
The Soviets, however, don't seem to feature as much in such discussions. On one hand, it makes sense: the Red Army was fighting across a very wide frontage, on harsh terrain and with a conscript army raised under wartime conditions - it only made sense for them to stick with simpler equipment that were easier to supply and maintain. The rapid loss of territory and industrial capacity at the beginning of the war probably didn't do much good for the tech department, either. On the other hand, the Soviets came up with many successful pieces of military technology in the post-war years, such as the T-54/55 main battle tank and the MiG-15 jet fighter, so obviously they didn't just spend the war scrapping together cheap trash either.
Off the top of my head, I can name three innovations that put the Soviets ahead in their respective fields:
What have I been missing? Were there significant, functional wartime innovations by the Soviets - in terms of weapons, command and control, logistics or otherwise - that most people haven't read about? Thanks a lot in advance!
So I'm just going to name a single one that pops out the most when I think of WW2 Soviet military developments (I hope that's okay), which is Soviet deep battle.
I'll try to briefly describe it, but there are people who are more qualified for that on this sub, that have already done so in more depth here.
In short: Soviet deep battle is a doctrine developed over the course of WW2. Not nearly as famous as for example the Katyusha you mentioned, but it could be argued it had a far larger impact than the latter. Soviet deep battle paved the way for 'operational art', a step in between the strategic and tactical level, that would later on become the standard for armies. It emphasized breakthrough and deep ^(think: hundreds of kilometers deep) penetration into enemy lines. These breakthroughs were done with relatively small groups (army size) and relied greatly on qualities such as deception and overwhelming firepower to breakthrough, after which more (preferably mobile) troops (army groups) would pour through the lines and advance far and wide, while destroying soft targets, eventually destroying the entire front line of the enemy.
It encompasses more things than just what I mentioned here, but these are very hard to summarize and your main question was about innovations in general, so instead I recommend reading The evolution of Operational Art if you wish to learn more about the subject.
This is far from a complete list, but off the top of my head:
Cast armour. The Soviets figured out pretty quickly that casting complex pieces of armour was easier than cutting them out and welding them in several pieces. The tradeoff was that the armour was about 10% weaker, which meant that the part had to be thicker, but widespread use of casting was very common. The use of variable thickness armour allowed the Soviets to have tanks with equal protection to German ones at a fraction of the weight. The Americans came to the same conclusion and also used casting extensively in the manufacture of medium tanks.
Automatic welding. Boris Paton's automatic welding method was received with skepticism, by technologists at the time, but it allowed for a consistent high quality weld, even if the operation of the mechanism was performed by a weak or unskilled labourer. This also allowed for drastic increases in tank production.
Night vision. The Germans are well known for having night vision equipment in limited service in 1945, but small batches of Soviet tanks had night vision equipment in 1942, and a night vision sight for the PPSh was accepted into service in 1943, although it's unlikely that it was built in large numbers either.
Sources:
A. Ulanov, D. Shein Perviye T-34
A. Solyankin et al Sredniy Tank T-34 1939-1945
A. Ulanov Sovetskiye Nochniye
P. Samsonov Night Vision and Mine Rollers
P. Samsonov Night Vision