Trivia

The XB-51 serving as the film's Gilbert XF-120 did not survive the making of the film. While in the process of shooting additional flight footage, the pilot attempted to get the plane to lift without the full thrust required, with the result that the plane prematurely rotated and stalled, crashing at the end of the Edwards runway. The crash killed pilot Major James R. Rudolf and radar officer Staff Sgt. Wilbur R. Savage, and destroyed the only surviving prototype of the plane.

Feature film debut of James Garner but Garner earlier appeared in the RKO production Juana de Arco (1948) as a tumbler. He also appeared in Warner Bros.' The Girl He Left Behind (1956), which was released approximately one week before, but shot one month after, Toward the Unknown (1956).

The scene with William Holden losing control and tumbling in the X-2 is depicted with footage from test pilot Chuck Yeager's 70,000-foot free-fall in the Bell X-1A in 1953.

The uncredited little boy playing James Garner's son is five-year-old actor Jon Provost who a year later would start playing "Timmy" in the TV series Lassie (1954).

Second of two films in which William Holden and Charles McGraw played military pilots with McGraw being Holden's immediate superior. The first was The Bridges at Toko-Ri (1954).