Carey Wilson narrates this short subject about the atomic bomb testing carried out in Nevada. At the time this movie was made, about twenty nuclear bombs had been detonated in the Silver State. Over the course of this short, about half that number of mushroom clouds arise on the screen.
The movie makes clear -- within, as Wilson notes, the issue of security -- that the purpose of running these tests is to ascertain the effects on structures, including the planes which release the bombs, and those within the blast and radiation perimeters. Here is discussion of the safety procedures taken for those who participate.