Under the Lend-Lease policy of March 1941, the US agreed to supply its Allies with food, oil and weaponry until the end of the war. In return, the US leased army and naval bases in Allied territories. When the Lend-Lease policy was established, the US was neutral; in December 1941, it joined the war after the Japanese bombed Pearl Harbour. The US had supply routes in the Atlantic, Indian and Pacific Oceans. The Soviet Union, a valued ally, was the recipient of a large proportion of US supplies. US-supplied Studebaker trucks were used by the Red Army to send troops and supplies along dirt roads to the frontline. The North Atlantic supply route was the most dangerous because ‘wolf packs’ of German U-boats preyed on US supply ships. By 1942, U-boats had sunk 828,000 tons of shipping along the US east coast. Ocean-going convoys, where large numbers of merchant ships were escorted by destroyers or battleships, helped to deter U-boat attacks.