Hundreds of extras were brought in to shoot the picture, and some 300 pilots were involved in the filming. Because the aerial battles required ideal weather to shoot, the production team had to wait on one occasion for 18 consecutive days for proper conditions in San Antonio. If possible, Wellman attempted to capture footage in the air in contrast to clouds in the background, above or in front of cloud banks to generate a sense of velocity and danger. Wellman later explained, "motion on the screen is a relative thing. A horse runs on the ground or leaps over fencers or streams. We know he is going rapidly because of his relation to the immobile ground". Against the clouds, Wellman enabled the planes to "dart at each other", and to "swoop down and disappear in the clouds", and to give the audience the sense of the disabled planes plummeting. During the delay in the aerial shooting, Wellman extensively rehearsed the scenes for the Battle of Saint-Mihiel over ten days with some 3500 infantrymen. A large battlefield with trenches and barbed wire was created on location for the filming. Wellman took responsibility for the meticulously-planned explosions himself, detonating them at the right time from his control panel. According to Peter Hopkinson, at least 20 young men, including cameraman William Clothier, were given hand-held cameras to film "anything and everything" during the filming.