This is Fat Man, the second atomic weapon ever used in war. It was dropped on August 9, 1945 by the United States on Nagasaki, Japan. This is a replica of the containment structure of the bomb, and is on display at the National Atomic Museum outside of Albuquerque (NM).

The first atomic bomb was dropped three days earlier on Hiroshima.

Another view is at the White Sands Missle Range Web site. Also see these other links.