Cash and carry was a diplomatic trade policy set in place by the FDR administration; it was crafted during a special session of the U.S. Congress on September 21, 1939, as a result of the outbreak of the Second World War in Europe. It replaced the Neutrality Act of 1937, by which belligerent parties would purchase only non-military goods from the United States so long as the client states in question paid in cash at the time of purchase and assumed full responsibility for transportation. The 1939 "Cash and Carry" revision allowed for the purchasing of military arms to belligerents on the same cash-and-carry basis.
The purpose of the policy was to maintain neutrality between the United States and European nations while giving aid to Britain by allowing them to buy non war materials.
Another article on American neutrality can be read here...
