The Lend-Lease Act allowed the officially neutral United States to become what Roosevelt called the 'arsenal of democracy,' shipping tanks, aircraft, and food to nations fighting Axis powers. Over the course of the war the U.S. sent more than $50 billion in aid, decisively tipping the balance of resources toward the Allies while keeping America formally out of combat for nine more months.
For eighteen months, Roosevelt had watched Britain fight alone against Nazi Germany while American isolationist sentiment, hardened by the trauma of World War I, blocked direct intervention. His solution was a legal sleight of hand: rather than selling or lending weapons outright, which cash-strapped Britain couldn't afford anyway, the U.S. would lend or lease material with repayment terms deferred, in Roosevelt's famous analogy, like lending a garden hose to a neighbor whose house is on fire.
The bill passed Congress after bitter debate, with isolationist senators warning it was a step toward war, and Roosevelt signed it on March 11, 1941. Within weeks, American destroyers, aircraft, and ammunition began flowing across the Atlantic despite the constant threat of German U-boats.
By war's end, Lend-Lease aid had reached the Soviet Union, China, and dozens of other Allied nations, including 400,000 jeeps and trucks and 12,000 armored vehicles to the USSR alone. Stalin himself later credited American trucks and Spam with helping keep the Red Army moving during its most desperate campaigns.