from wikipedia:
http://en.wikipedia.org/...i/Lend-lease#Significance
Much of the aid can be better understood when considering the economic distortions caused by the war. Most belligerent powers cut back severely on production of nonessentials, concentrating on producing weapons. This inevitably produced shortages of related products needed by the military or as part of the military-industrial complex.
The USSR was highly dependent on rail transportation, but during the war practically shut down rail equipment production: only about 92 locomotives were produced. 2,000 locomotives and 11,000 railcars were supplied under Lend-Lease. The USSR had a pre-war stock of over 25,000 locomotives and 600,000 railcars. The Lend-Lease stock did not start being shipped until 1944.[citation needed] Likewise, the Soviet air force received 18,700 aircraft, which amounted to about 14% of Soviet aircraft production (19% for military aircraft).[7]
Although most Red Army tank units were equipped with Soviet-built tanks, their logistical support was provided by hundreds of thousands of U.S.-made trucks. Indeed by 1945 nearly two-thirds of the truck strength of the Red Army was U.S.-built. Trucks such as the Dodge 3/4 ton and Studebaker 2 1/2 ton, were easily the best trucks available in their class on either side on the Eastern Front.[citation needed]U.S. supplies of telephone cable, aluminum, canned rations, and clothing were also critical.
Lend Lease was a critical factor that brought the U.S. into the war, especially on the European front. Hitler cited the Lend-Lease program when he declared war on the U.S. on 11 December 1941.
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Personally I doubt that the soviet union would have won had the Third Reich been at war only with them. The soviet union got a *ton* of aid from the US, but more importantly, as others mentioned, the strategic bombing of Nazi Germany seriously hurt their economy; a germany free from bombing, able to focus entirely on the USSR would have rolled them up much more nicely; plus, had they not been at war in the west, they may have started operation barbarosa on time, and botten to moscow earlier.....