This silent film shows the final preparation and loading of the "Fat Man" bomb into "Bockscar," the plane which dropped the bomb on Nagasaki. It then shows the Nagasaki explosion from the window of an observation plane. This footage comes from Los Alamos National Laboratory. I have not edited it in any way from what they gave me except to improve the contrast a little — it is basically "raw." I have annotated it with some notes on the bombing and what you can see — feel free to disable it if you don't want it.
I suggest leaving them on. This is the first time I've ever seen a video benefit from YouTube annotations! [via Nuclear Secrecy and MeFi]