The Allies were always able to ship war supplies to Russia through Murmansk and Archangel - that is where the vast majority of the 10 million tons of strategic raw materials and the thousands and thousands of tanks,trucks,planes,and even boots sent to the Soviet Union by USA and Britain during WW2 were landed.
In the Winter,when ice made these ports unusable,aid was shipped through Iran.However,this was only for a few months each year,most of the aid was shipped to Murmansk and Archangel.
So,your question is based on an entirely false premise,as the Allies were able to get war supplies to Russia year round.
Hope this helps!
