British efforts to aid the Soviet Union in the early months of the war in the East are underexplored and simplified in the historiography of Allied supply to Russia during the Second World War. In fact, British leaders recognized within weeks of the German invasion that the Eastern Front was the most important front in the war against Nazi Germany and that the Soviets were likely to continue to resist for a long time. Britain then became increasingly committed to supplying the Soviets with material aid. Given the difficulties involved, and Soviet uncooperativeness, British aid prior to the Moscow Supply Conference was substantial and relatively swift. The expansion of aid into a large scale effort, later established on a lend-lease basis, had its origins in the evolution of British assessments and priorities over the summer of 1941.