The program was under the direct control of the White House, with Roosevelt paying close attention, assisted by Harry Hopkins, W. Averell Harriman, and Edward Stettinius Jr.. Roosevelt often sent them on special missions to London and Moscow, where their control over Lend Lease gave them importance. The budget was hidden away in the overall military budget, and details were not released until after the war.
A total of $50.1 billion (equivalent to $681 billion presently) was involved, or 11% of the total war expenditures of the U.S. In all, $31.4 billion (equivalent to $427 billion today) went to Britain and its Empire, $11.3 billion (equivalent to $154 billion today) to the Soviet Union, $3.2 billion (equivalent to $43.5 billion today) to France, $1.6 billion (equivalent to $21.7 billion today) to China, and the remaining $2.6 billion to the other Allies. Reverse lend-lease policies comprised services such as rent on bases used by the U.S., and totaled $7.8 billion; of this, $6.8 billion came from the British and the Commonwealth, mostly Australia and India. The terms of the agreement provided that the materiel was to be used until returned or destroyed. In practice very little equipment was in usable shape for peacetime uses. Supplies that arrived after the termination date were sold to Britain at a large discount for £1.075 billion, using long-term loans from the United States. Canada was not part of Lend Lease. However it operated a similar program called Mutual Aid that sent a loan of $1 billion and $3.4 billion in supplies and services to Britain and other Allies.
This program effectively ended the United States' pretense of neutrality and was a decisive change from non-interventionist policy, which had dominated United States foreign relations since 1931. (See Neutrality Acts of 1930s.)
After the defeat of France during June 1940, the British Commonwealth and Empire were the only forces engaged in war against Germany and Italy, until the Italian invasion of Greece. Britain had been paying for its material with gold as part of the "cash and carry" program, as required by the US Neutrality Acts of the 1930s, but by 1941 it had liquidated so many assets that its cash was becoming depleted.
During this same period, the U.S. government began to mobilize for total war, instituting the first-ever peacetime draft and a fivefold increase in the defense budget (from $2 billion to $10 billion). In the meantime, as the British began becoming short of money, arms, and other supplies, Prime Minister Winston Churchill pressed President Franklin D. Roosevelt for American help. Sympathetic to the British plight but hampered by public opinion and the Neutrality Acts, which forbade arms sales on credit or the loaning of money to belligerent nations, Roosevelt eventually came up with the idea of "lend–lease". As one Roosevelt biographer has characterized it: "If there was no practical alternative, there was certainly no moral one either. Britain and the Commonwealth were carrying the battle for all civilization, and the overwhelming majority of Americans, led in the late election by their president, wished to help them." As the President himself put it, "There can be no reasoning with incendiary bombs."
In September 1940, during the Battle of Britain the British government sent the Tizard Mission to the United States. The aim of the British Technical and Scientific Mission was to obtain the industrial resources to exploit the military potential of the research and development work completed by the UK up to the beginning of World War II, but that Britain itself could not exploit due to the immediate requirements of war-related production. The shared technology included the cavity magnetron (key technology at the time for highly effective radar; the American historian James Phinney Baxter III later called "the most valuable cargo ever brought to our shores"), the design for the VT fuze, details of Frank Whittle's jet engine and the Frisch–Peierls memorandum describing the feasibility of an atomic bomb. Though these may be considered the most significant, many other items were also transported, including designs for rockets, superchargers, gyroscopic gunsights, submarine detection devices, self-sealing fuel tanks and plastic explosives.
During December 1940, President Roosevelt proclaimed the U.S.A. would be the "Arsenal of Democracy" and proposed selling munitions to Britain and Canada. Isolationists were strongly opposed, warning it would result in American involvement with what was considered by most Americans as an essentially European conflict. In time, opinion shifted as increasing numbers of Americans began to consider the advantage of funding the British war against Germany, while staying free of the hostilities themselves. Propaganda showing the devastation of British cities during The Blitz, as well as popular depictions of Germans as savage also rallied public opinion to the Allies, especially after the defeat of France.