FDR signs the Lend-Lease Act March 1941; Wikimedia Commons

Diverging from a non-interventionist policy begun after WWI, in March 1941 the U.S. Congress  enacted Public Law 77-11, the Lend-Lease Act.

Formally titled : An Act to Further Promote the Defense of the United States, the law authorized a program that supplied the United Kingdom, USSR, Republic of China, Free France and other Allied nations with war materiel.