Actually, Jack Northrop had begun work on flying wing aircraft as early as the late 1920s, and flew a his first (albeit with a tail boom) when the elder Horton was only 15. A series of scaled designs in the early 40's resulted in the post-war YB-35 and YB-49, which are both roughly the same dimensions as the current…

Bell and Williams Research (now International) built a jet belt in the early 1960s. They didn't call it a "jet pack" but it was powered by a jet engine.