These declassified photos reveal the preparations leading up to the bombings of Hiroshima and Nagasaki. On August 6th and 9th of 1945, atomic bombs were dropped on the two cities.

Here are the previously unseen pictures of the final preparations:

Soldiers checking the casings of the "Fat Man" atomic bomb

National Archives

Geophysicist Francis Birch (left) marks "Little Boy" L-11 as Norman Ramsey, who would later win the Nobel Prize in Physics, looks on. This is the actual atomic bomb dropped on Nagasaki.

National Archives

Final bomb assembly

National Archives

Fat Man nearly assembled and ready to be placed inside its casing.

National Archives

A technician puts putty to the forward polar plate of "Fat Man."

National Archives

Sealant is applied using a spray gun.

National Archives

National Archives

A frame taken from a colored movie, showing the color of the device and sealant/putty.

National Archives

Workers and soldiers sign their names and write messages on the "Fat Man."

National Archives

A closer look.

National Archives

“A Second Kiss for Hirohito!” signed by Rear Admiral W.R. Purnell, USN on the side of the "Fat Man".

National Archives

Fully-assembled "Fat Man" loaded onto a transport trailer.

National Archives

The bomb being transported to the airfield, under cover with an escort.

National Archives

A bomb pit on the airfield.

National Archives

The bomb pits, measuring roughly 8 feet by 12 feet, still exist today.

(L) National Archives/ (R) Jeffrey Tripp/FLICKR

Soldiers ready for the preliminary pit alignment.

National Archives

National Archives

The bomb's alignment was checked over very carefully by eye and hand.

National Archives

They made sure everything's in place while the MPs kept watch.

National Archives

National Archives

With the use of a hydraulic lift, they lowered the bomb and its trailer into the pit.

National Archives

National Archives

Workers check "Little Boy" for the very last time. Still covered with tarp for security reasons.

National Archives

Now the aircraft Enola Gay, a Boeing B-29 Superfortress bomber, is backed up slowly over the pit.

National Archives

The cover is removed and the bomb is prepared for loading.

National Archives

National Archives

"Little Boy" is raised using a hydraulic lift and gets loaded into the belly of Enola Gay.

National Archives

National Archives

National Archives

After the bomb is secured inside the plane, all connections and equipment are re-checked.

National Archives

From there, "Little Boy" and "Fat Man" were flown over Hiroshima and Nagasaki, respectively, and dropped World War II ended shortly afterwards.

National Archives / Charles Levy / AP

H/T: Atchuup