U.S. World War II Nuclear Weapons

References:
History of Project A by N.F. Ramsey (1.6 MB PDF)

Mark I “Little Boy”

Length: 126 inches
Diameter: 30 inches
Weight: 8,900 lbs
Yield: 15~ kilotons

Unit Designation

Notes

L-1

All non-nuclear components assembled and dropped near Tinian on 23 July 1945. Test was a complete success, the device's radar fuze successfully firing in mid-air.

L-2

All non-nuclear components assembled and dropped near Tinian on 24 July 1945. Test was a complete success, the device's radar fuze successfully firing in mid-air.

L-5

All non-nuclear components assembled and dropped near Tinian on 25. July 1945. Test was a complete success, the device's radar fuze successfully firing in mid-air.

L-6

Assembled device with non-nuclear components was used on Iwo Jima on 29 July 1945 to perform a successful test of procedures for emergency reloading of a live unit from a Silverplated B-29 onto another aircraft.

After this test it was flown to Tinian, where on 31 July 1945 a full up drop test was conducted. The device's radar fuze operated as intended.

L-11

Assembled during the night of 5 August 1945 with active nuclear components. The fissile projectile had been delivered on 26 July 1945 by the USS Indianapolis, and the fissile target insert had arrived during the night of 28/29 July 1945 on three otherwise empty ATC C-54s.

The assembled device was placed onto it's transport trailer and sent to the loading pit after 1400 Hours on 5 August 1945. At 1500 hours, B-29-45-MO #44-86292 was backed over the loading pit and the device was loaded shortly afterwards.

Final testing of the unit at the ready hardstand did not finish until 1800 Hours 5 August.

The loaded B-29 took off at 0245 Hours 6 August. At 0730 Hours, the RED arming plugs were inserted, arming the device. At 0847 Hours, all ARCHIES were tested with positive results.

Dropped at 0915 ½ Hours. After falling for 43 seconds, the device was initated at 1,900 feet over Hiroshima. Yield was about 15 kilotons.

L-11 Being Assembled
L-11 in Loading Pit

Model 1561 “Fat Man”

Length: 128 inches
Diameter: 60 inches
Weight: 10,300 lbs
Yield: 21~ kilotons

Notes: 2,830 pounds of the Model 1561's weight was a 3/8 inch (9.52 mm) thick steel case intended to protect the device from antiaircraft fire as it descended to the target.

Unit Designation

Notes

F-13

Special inert unit assembled on 1 August 1945 with cast plaster blocks standing in for explosives. Used to test electronics and fuzing.

F-18

Special inert unit similar to F-13 assembled for a drop on 3 August 1945. However due to uncertainity on how internal venting of the sealed unit would work; the barometric switches were modified and the unit dropped on 5 August 1945. Electronics and fuzing system functioned as designed.

F-31

Active unit. Scheduled for dropping on 11 August 1945 (At one point it was 20 August). Advanced two days to 9 August 1945.

Device was fully assembled, loaded, and checked out on B-29-36-MO #44-27297 by 2200 hours on 8 August 1945.

The loaded B-29 took off at 0347 hours on 9 August 1945. At 0400 hours the RED plugs were inserted, arming the device.

Dropped at 1158 Hours. Initation was at 1,650 feet over Nagasaki. Yield was about 21 kilotons.

F-32


F-33

Identical to “active” device except for substitution of lower quality explosive lens. Components arrived on Tinian on 2 August 1945 at 1230 hours. Assembly began later that day. Fully ready by 5 August 1945, but not dropped until 8 August 1945 due to lack of key personnel and aircraft which were tied up in the L-11 LITTLE BOY mission against Hiroshima. Device functioned as designed.

F-101


F-102


F-103