The only surviving Ho 229 - German WW2 aircraft, the first pure flying wing powered by jet engines. 1944.
In the United States, from the 1930s Jack Northrop and Cheston L. Eshelman autonomously dealt with their own plans. The Northrop N-1M, a scale model for a long-range aircraft, first flew in 1940. The Eshelman FW-5, which was regularly alluded to as The Wing, was a trial lodge monoplane.