DerAdlerIstGelandet said:
Horton was experimenting with them before Northrop though I believe. I believe Horton was experimenting with flying wing gliders in the early 30's but I may be mistaken.
Northrop built an all-wing airplane in 1927.
The first glider, the Horten Ho I, was first flight tested at Bonn-Hagelar in July 1933.