Even though the U.S. was desperately trying to build up its military forces throughout 1941, Roosevelt decided to give the British some of the United States' most advanced weapons. Military aid to Britain was greatly facilitated by the Lend-Lease Act of March 11, 1941, in which Congress authorized the sale, lease, transfer, or exchange of arms and supplies to "any country whose defense the president deems vital to the defense of the United States." Related Objects
Even so, Churchill’s appointment as minister of munitions in July 1917 was made in the face of a storm of Tory protest. Excluded from the cabinet, Churchill’s role was almost entirely administrative, but his dynamic energies thrown behind the development and production of the tank (which he had initiated at the Admiralty) greatly speeded up the use of the weapon that broke through the deadlock on the Western Front. Paradoxically, it was not until the war was over that Churchill returned to a service department. In January 1919 he became secretary of war. As such he presided with surprising zeal over the cutting of military expenditure. The major preoccupation of his tenure in the War Office was, however, the Allied intervention in Russia. Churchill, passionately anti-Bolshevik, secured from a divided and loosely organized cabinet an intensification and prolongation of the British involvement beyond the wishes of any major group in Parliament or the nation—and in the face of the bitter hostility of labour. And in 1920, after the last British forces had been withdrawn, Churchill was instrumental in having arms sent to the Poles when they invaded the Ukraine.
The following year was equally crucial, witnessing Germany’s attack on Russia and America’s entry into the war. Churchill had already established a warm relationship with President Franklin Roosevelt and put aside an instinctive dislike and distrust for Soviet premier Joseph Stalin. Churchill, a firm anticommunist, knew Stalin for what he was—unlike Roosevelt, who consistently made allowances for the Soviet dictator, fondly calling the genocidal despot ‘‘Uncle Joe.’’ Despite their personal and national differences with respect to communist Russia, Churchill and Roosevelt remained staunch allies throughout the war. They quickly decided on a ‘‘Germany first’’ strategy, but in early 1942 the main threat was from Japan, which was rolling up easy victories in the Philippines, Singapore, and Malaya.

Churchill Speech