SECTION 7 – NAGASAKI ATOMIC BOMBING

ATOMIC BOMBINGS OF
HIROSHIMA & NAGASAKI (1945)

Replica “Fat Man”
Atomic Bomb

(Nagasaki)

The Official Story

“FAT MAN” ATOMIC BOMB
(Nagasaki)

“Fat Man” (also known as Mark III) is the codename for the type of nuclear bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 1945. It was the second of the only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation marked the third nuclear explosion in history. It was built by scientists and engineers at Los Alamos Laboratory using plutonium from the Hanford Site, and it was dropped from the Boeing B-29 Superfortress Bockscar piloted by Major Charles Sweeney.

The name Fat Man refers to the early design of the bomb because it had a wide, round shape. Fat Man was an implosion-type nuclear weapon with a solid plutonium core. The first of that type to be detonated was the Gadget in the Trinity nuclear test less than a month earlier on 16 July at the Alamogordo Bombing and Gunnery Range in New Mexico. Two more were detonated during the Operation Crossroads nuclear tests at Bikini Atoll in 1946, and some 120 were produced between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb. The Fat Man was retired in 1950.

Bombing of Nagasaki

Bomb assembly

The first plutonium core was transported with its polonium-beryllium modulated neutron initiator in the custody of Project Alberta courier Raemer Schreiber in a magnesium field carrying case designed for the purpose by Philip Morrison. Magnesium was chosen because it does not act as a tamper. It left Kirtland Army Air Field on a C-54 transport aircraft of the 509th Composite Group’s 320th Troop Carrier Squadron on 26 July and arrived at North Field on Tinian on 28 July. Three Fat Man high-explosive pre-assemblies (designated F31, F32, and F33) were picked up at Kirtland on 28 July by three B-29s: Luke the Spook and Laggin’ Dragon from the 509th Composite Group’s 393d Bombardment Squadron, and another from the 216th Army Air Forces Base Unit. The cores were transported to North Field, arriving on 2 August, when F31 was partly disassembled in order to check all its components. F33 was expended near Tinian during a final rehearsal on 8 August. F32 presumably would have been used for a third attack or its rehearsal.

On 7 August, the day after the bombing of Hiroshima, Rear Admiral William R. Purnell, Commodore William S. Parsons, Tibbets, General Carl Spaatz and Major General Curtis LeMay met on Guam to discuss what should be done next. Since there was no indication of Japan surrendering, they decided to proceed with their orders and drop another bomb. Parsons said that Project Alberta would have it ready by 11 August, but Tibbets pointed to weather reports indicating poor flying conditions on that day due to a storm and asked if the bomb could be made ready by 9 August. Parsons agreed to try to do so.

Fat Man F31 was assembled on Tinian by Project Alberta personnel, and the physics package was fully assembled and wired. It was placed inside its ellipsoidal aerodynamic bombshell and wheeled out, where it was signed by nearly 60 people, including Purnell, Brigadier General Thomas F. Farrell, and Parsons. It was then wheeled to the bomb bay of the B-29 Superfortress named Bockscar after the plane’s command pilot Captain Frederick C. Bock, who flew The Great Artiste with his crew on the mission. Bockscar was flown by Major Charles W. Sweeney and his crew, with Commander Frederick L. Ashworth from Project Alberta as the weaponeer in charge of the bomb.

Bombing of Nagasaki

Bockscar lifted off at 03:47 on the morning of 9 August 1945, with Kokura as the primary target and Nagasaki the secondary target. The weapon was already armed, but with the green electrical safety plugs still engaged. Ashworth changed them to red after ten minutes so that Sweeney could climb to 17,000 feet (5,200 m) in order to get above storm clouds. During the pre-flight inspection of Bockscar, the flight engineer notified Sweeney that an inoperative fuel transfer pump made it impossible to use 640 US gallons (2,400 l) of fuel carried in a reserve tank. This fuel would still have to be carried all the way to Japan and back, consuming still more fuel. Replacing the pump would take hours; moving the Fat Man to another aircraft might take just as long and was dangerous as well, as the bomb was live. Colonel Paul Tibbets and Sweeney therefore elected to have Bockscar continue the mission.

The target for the bomb was the city of Kokura, but it was found to be obscured by clouds and drifting smoke from fires started by a major firebombing raid by 224 B-29s on nearby Yahata the previous day. This covered 70% of the area over Kokura, obscuring the aiming point. Three bomb runs were made over the next 50 minutes, burning fuel and repeatedly exposing the aircraft to the heavy defenses of Yahata, but the bombardier was unable to drop visually. By the time of the third bomb run, Japanese anti-aircraft fire was getting close; Second Lieutenant Jacob Beser was monitoring Japanese communications, and he reported activity on the Japanese fighter direction radio bands.

Sweeney then proceeded to the alternative target of Nagasaki. It was obscured by clouds, as well, and Ashworth ordered Sweeney to make a radar approach. At the last minute, however, bombardier Captain Kermit K. Beahan found a hole in the clouds. The Fat Man was dropped and exploded at 11:02 local time, following a 43-second free-fall, at an altitude of about 1,650 feet (500 m). There was poor visibility due to cloud cover and the bomb missed its intended detonation point by almost two miles, so the damage was somewhat less extensive than that in Hiroshima.

An estimated 35,000–40,000 people were killed outright by the bombing at Nagasaki. A total of 60,000–80,000 fatalities resulted, including from long-term health effects, the strongest of which was leukemia with an attributable risk of 46% for bomb victims. Others died later from related blast and burn injuries, and hundreds more from radiation illnesses from exposure to the bomb’s initial radiation. Most of the direct deaths and injuries were among munitions or industrial workers.

Mitsubishi’s industrial production in the city was also severed by the attack; the dockyard would have produced at 80 percent of its full capacity within three to four months, the steelworks would have required a year to get back to substantial production, the electric works would have resumed some production within two months and been back at capacity within six months, and the arms plant would have required 15 months to return to 60 to 70 percent of former capacity. The Mitsubishi-Urakami Ordnance Works, which manufactured the type 91 torpedoes released in the attack on Pearl Harbor, was destroyed in the blast.

Source: Wikipedia