America had prototype jets, experimentals, during WWII. When the Joint Chiefs discovered that the Nazi's had made an experimental test of an atomic bomb they decided that Germany had to be taken quickly. There wasn't time to reconfigure America's war production for jet planes. Germany had to be taken in a matter of months. Hence the horrific bombing of Germany. America used thousands of bombers and fire bombing technique to stop Germany before they could deploy nuclear weapons.
Also, America produced rocket planes in preparation for the possibility of Hortan bombers with nuclear weapons. The X-15 was an experimental rocket plane taken from the WWII designs.