In the summer of 1941 three million German troops attacked the Soviet Union launching the largest military invasion in history.
The surprise attack brought the Soviets into the war on the Allied side and saw the Red Army engage in a titanic four-year battle with the Nazi invaders.
While the war may ultimately have ended with the hammer and sickle flying over Berlin, in 1941 and 1942 German victory seemed inevitable as Hitler's forces blitzkrieged their way ever eastward capturing vast tracts of Soviet territory.
Prime Minister Winston Churchill knew Britain's hopes of winning the war depended on keeping the Red Army fighting so he committed to supplying the Soviets with munitions and materials to help them continue the battle.
The only way of transporting supplies to Russia from the United Kingdom and North America was to send merchant ships through the waters off German-occupied Norway and in to the Arctic Ocean then on to the northern Russian ports of Archangel and Murmansk.
The merchant ships sailed with Royal Navy escorts to protect them from air and submarine attacks, but as well as the enemy the convoys had to contend with freezing temperatures and raging seas.
Starting in August 1941, the convoys continued carrying vital supplies to Russia until the end of the war in 1945.
Many men and ships were lost and the sailors endured torrid conditions but the convoys achieved Churchill's goal and kept the Soviet Union fighting.
Arctic convoys by numbers: