The correct answer is the Lend Lease Act.
If you are referring to World War II, the US maintained their policy of neutrality by implementing the Lend Lease Act. This law allowed the US to lease military equipment and resources to members of the Allied forces during World War II. If the resources were damaged, then the country borrowing them agreed to fix/pay for a replacement. If it was not used, it would be returned to the United States after the war.