I guess I have little to add to what everyone has stated. Let me rephrase my own post then so maybe you understand it a little better:
in 1941 and even in 42 the USSR had the utter bulk(meaning not everything) of its industry on RAILS, I am very sure using a industrial machine half disassembled inside a rail wagon does NOT work.
As such the USSR production within the time frame of 41 and 42 was abysmal (by USSR standard). There for the meager little aid that they did get from the USA was most needed. It does not mean that in terms of production they relied on the USA because the USSR couldn't produce anything themselves, it simply means they had a bad year, after which they recovered and started a production line that could be match by very few nations (essentially the USA only).
They continued to receive lend lease after 42, but these quantities where not very significant compared to the USSR's own production.
People seem to forget that the USSR was about to collapse and get annexed in 41 and 42, and you seem to forget that its industry was NOT operational during these critical 2 years. At such a low in the war any tank from anyone would have been a huge gift. So long as it helped them survive just long enough to get their own production back up.
So yes the USSR produced far more then it got in lend-lease (over the course of the entire war), I am not debating that issue, I am merely stating that what they got in 41 and 42 was at such a critical moment that it actually mattered. Many soviet tank divisions where half Russian half English in tanks (obviously crew being all Russian), yes even the UK gave a lend-lease to Russia, mostly in old obsolete tanks. Obviously the matter of half British tank divisions counts for the early day's in 41 - 42, after that their own tanks(which where superior anyway) where rolling off the assembly lines in huge numbers.
The USSR was not going to collapse, or get annexed in 1941 or 1942. The entire premise is a fallacy, and it is ludicrous to even suggest it as a possibility. This is a somewhat complex problem, so I will attempt to explain it.
We are talking about expectation, versus reality. The idea that the USSR was going to collapse and be annexed is based on the German expectation. The problem is, the German expectation was not grounded in reality. Their reality, was "We will invade, beat them up, take a couple of places on the map and they will collapse". They never pondered the possibility of "what if they don't just collapse". As we know, the USSR didn't collapse. Nor was it ever even realistically considered.
Your argument seems to, and I don't want to put words in your mouth, but it seems to suggest that Lend Lease somehow saved the USSR from this so called imminent collapse. This is, not grounded in reality.
Here is reality. The USSR lost around 5 million men irrecoverably in the first three months of the war. The German military reached their 2 objectives, Leningrad and Moscow, and they shattered the Soviet military in the process. What Lend Lease had the USSR recieved by this point? Nothing. The British went on to send something like 500 obsolete tanks before the battle for Moscow, of which a dozen or so actually took part. That is the most meaningful Lend Lease contribution to the actual turning point of the war. You see, Germany invaded, caught the USSR mostly by suprise and eviscerated the Soviet armies. Marched to Moscow and Leningrad and looked to be on the verge of accomplishing their strategic goals.
A quick aside. Even if Germany takes Moscow and Leningrad, nothing changes. The USSR still continues to fight. This is where we can reference expectation versus reality. Reality is, even if Moscow is lost the USSR continues to fight and Germany is only marginally closer to accomplishing what most modern military historians now consider to be an impossible endeavor. So we are going to carry on this fun little fantasy. That being, IF the USSR could have lost the war to Germany, December 1941 was the CLOSEST to that point of defeat it would ever be. Germany at its strongest, Russia at its weakest. Germany at the gates of Moscow. No outside help that would make a strategic difference was coming in 1941.
What happened? The Soviets between June and December raised the equivalent manpower of 800 rifle divisions. Many of these divisions (no, sorry Siberians didn't save Moscow), took part in Moscow. Again what happened? The Soviets attacked with mass and determination in the dead of winter and drove the Germans back. They took the entire operational impetus around Moscow AND Leningrad away from Germany. The following summer some German general staff officers said that Germany had already lost the ability to win the war by military means, again that is summer 1942 some in the general staff were voicing this issue. What is the state of Lend Lease? It's trickling in in 1942. It's something, but it isn't much.
The greatest threat to the survival of the USSR ended in December 1941, before outside help was flowing in. The German general staff in fact knew that they had lost the ability to take Moscow and that is why in 1942 you see a total shift in the operational axis of the German military. Moscow is considered lost, so they shift towards the Caucasus mountains.
What does this shift represent in real terms. It represents that Germany no longer believes it can win a quick decisive war, the perception we talked about earlier in this post. The perception that if we beat them up and take a couple of cities they will collapse. That is what Case Blue represents. It represents a shift from a decisive victory to preparing for a long, drawn out, economic and attrition based campaign in which cutting off oil from Baku could be telling.
That is why Germany lost the ability to win the war in 1941 at the Gates of Moscow. Lend Lease didn't rescue the USSR. Lend Lease didn't enable the USSR to win. It helped them win faster.