What did the US do while remaining officially neutral to guide the course of the war?

While the U.S. remained neutral, they secretly aided the British with arms and other essential items. This was part of the Lend Lease Act, which was designed to help England counter unrestricted German U-boat attacks in the Atlantic. This not only helped guide the course of the war, it also propelled the U.S. into finally entering the war and turning the tide in favor of the Allies.