Precautionary measures
mostly, which were ultimately ineffective because it was like a small dam made by beavers trying to hold back a flash flood. See, the Reds/Stalin didn't expect Germany to be
able to attack that soon; they thought they'd have enough time to ramp up and invade first. They thought these additional precautions would be enough to respond to a hypothetical German attack and infiltration at
that time.
Unfortunately, Stalin and the Soviets
heavily underestimated the Germans and Hitler, and they
were ready -- but sort of but not really.
See, while they
did attack early, were
sort of ready compared to the Reds, there were critical flaws in Germany's plans:
- They hoped to blitz all the way through the Soviet Union as they did France and other countries and win decisively before such supply issues would be a problem, since France and Poland were basically next door to Germany
- The taking of and reliance on Soviet oil infrastructure to supply their forces with critical fuel reserves
Germany's batshit insane gambit of zerg rushing worked...
initially.
After losing a
massive chunk of their territory from the German advance, the Soviets eventually managed to stabilize the front line, with the linchpin being Stalingrad which held. This basically fucked the German's over as their time basically run out.
The Germans basically repeated the mistake the French did centuries prior -- the infamous Russian Winter and supply lines.
They hadn't prepared for the killer cold because they didn't think they needed to, their supply lines were stretched thin, and they hadn't managed to take the oil fields which their strategy heavily relied upon. Soldiers
literally froze to death, fuel was limited, spare parts were nonexistent, and food and other essentials were scant and hard to come by.
The Soviets held, moved their production behind the Urals, ramped up said production while the enemy was banging on the gates, and then literally drowned the Germans with numbers, ironically counter-zerging them.
If the Soviets hadn't held Stalingrad and Germany won that battle, Russia would've been fucked... but so would Germany to ultimately a lesser extent, since Stalin ordered all the oil infrastructure further south to be scuttled if it were in danger of falling to the Germans.
Germany needed those oil fields not just for fuel but for war materiel production, after all.