In November 1942, i.e., at the height of the battle for the Caucasus and Stalingrad, the arms deliveries practically came to a complete halt. Disruptions in shipments had already begun in the summer of 1942, when German aircraft and submarines almost entirely wiped out the infamous Convoy PQ 17 that was abandoned (at the order of the Admiralty) by the British destroyers assigned to escort it. Tragically only 11 of the original 35 ships arrived safely into Soviet ports – a catastrophe that was used as a pretext to suspend subsequent convoys from Britain until September 1942.
A new convoy, the PQ 18, lost 10 of its 37 vessels along its route, and another convoy was not sent until mid-December 1942. Thus, for three and a half months, when one of the most decisive battles of the entire Second World War was being waged on the Volga, fewer than 40 ships carrying lend-lease cargo arrived intermittently in Murmansk and Arkhangelsk. For this reason, many were understandably suspicious that London and Washington were spending that time just waiting to see who would be left standing after the battle of Stalingrad.
As a result, between 1941 and 1942 only 7% of the wartime cargo shipped from the US made it to the Soviet Union. The bulk of the weapons and other materials arrived in the Soviet Union in 1944-1945, once the winds of war had decisively shifted.