The films that you are talking about are "documentary" films (as opposed to the "technical" films that the engineers and scientists actually expended the majority of the film on), and were made for military brass and elected officials. They were used as ways to brief the President and select members of Congress (e.g., the Joint Committee on Atomic ENergy) on the status of the nuclear testing program, which was itself an expensive program and involve the expenditure of (very expensive) fissile materials. They are a visually stimulating alternative to a traditional written report, which of course were produced in great volumes. We have some records of some of these films being screened at the White House, or in Congress, or eventually being released to the public (e.g., the 1952 Ivy Mike documentary was broadcast on TV in 1954).

The origins of these films appear to be with the Operations Crossroads test series in 1946. Crossroads, unlike the others, was not a secret test series, and international observers — even Soviets! — were invited to attend. In many respects it was exactly the opposite of the only previous nuclear test (Trinity), which was only observed by a relatively small number of people sworn to secrecy. The photography and film work was done by the military (who also ran the test in general, as the civilian Atomic Energy Commission did not yet exist).

After Crossroads, the military judged that a permanent photography unit be established in charge of the technical and documentary film production. They created a Top Secret studio in Los Angeles known as Lookout Mountain, and charged them with producing these film reports. After the end of atmospheric nuclear testing in 1962, their work shifted into other military topics, notably the war in Vietnam, until it was disbanded in 1968.