A significant number of extra casings were shipped to Tinian Island and used in various tests with “dummy” bombs which contained all the active components of a working atomic bomb, but no fissile material to test out and prove the assembly procedures for the actual devices themselves.
This unit was assembled with non-nuclear components and dropped on 23 July 1945. Test was a complete success.
Unknown whether this is a test unit or L-11; the unit dropped on Hiroshima.
This is the actual unit which was dropped on Nagasaki.
Final Bomb Assembly
Fat Man devices after they were assembled, underwent a final procedure outside the Assembly Building, where their crevices were filled with putty, and then over-sprayed with sealant to maintain the proper environment within the device during the time it would take to deliver it to the target.
Note the writing on the tail fin assembly and the logo on the bomb’s polar plate and on the worker’s coveralls.
This is a frame taken from a color movie taken of the sealant application, showing the color of the device and sealant/putty.
Once the device was virtually complete, workers began to sign their names and various exhortations onto the device.
The completed Fat Man device is being lowered/checked over on it’s transport dolly for the trip to the airfield.