Supplies to the Soviet Union had been sent via the North Cape to Murmansk and Archangel soon after the German invasion but the number of ships available was limited and convoys were vulnerable to German air and submarine attack. Supplies were also sent from American pacific ports to Vladivostok in Soviet-flagged ships but Allied planners wished to open another supply route through Iran. Though officially neutral, the Shah was widely viewed as pro-German by the allies. Following the Shah's refusal to open Iran up as a supply route for war materiel to the USSR; the allies invaded and occupied Iran in August 1941. The Shah, who urged his military not to resist the invasion, was deposed and his young son placed on the throne as titular head of an allied controlled puppet government. Iranian oil fields were secured and the line of supply to Russia established and maintained for the remainder of the war.