Fifty years ago today, the first of two atomic bombs was dropped on Japan. The Hiroshima bombing and the second, three days later at Nagasaki, brought World War II to an end. Atomic weapons--like the long bow, machine gun and submarine before them--forever changed the complexion of warfare. Half a century later, those bombs and their progeny continue to cast a shadow over our world--as the ultimate threat and the ultimate deterrent.
Mission Into History
Within two weeks of presidential approval, the first atomic bombing in history was complete. Here's how the drama unfolded. Hourly times are those on the Pacific Island of Tinian until the flight reaches Iwo Jima.
JULY 31
President Harry S. Truman issues final, handwritten order to use the bomb.
AUG. 1
On Tinian, mission commander and pilot Col. Paul Tibbets drafts order for mission, specifying number of planes to be used and personnel.
AUG. 5
2:15 p.m.: Orders arrive on Tinian confirming takeoff time in just over 12 hours.
3-3:30 p.m.: Sign painter gives the strike plane a new name, Enola Gay--after Tibbets' mother.
3:30 p.m.: The bomb, dubbed "Little Boy," leaves storage area and is winched into the Enola Gay.
Midnight: Tibbets gives final briefing to 26 men who will fly to Japan in the three planes. In the year he has been in command he has never used the words "atomic" or "nuclear." Now, he describes the weapon as "very powerful."
AUG. 6
2:45 a.m.: Enola Gay departs.
2:55 a.m.: Navigator Capt. Theodore van Kirk makes first log entry. Enola Gay is on its three-hour leg to the Iwo Jima rendezvous point.
3 a.m.: Weaponeer Capt. William Parsons begins to arm the bomb.
4:52 a.m. (Japan time, one hour behind Tinian): Enola Gay begins to circle over Iwo Jima.
4:55 a.m.: Great Artiste, carrying instruments to measure the blast, and No. 91, camera plane, arrive; all three ascend to 9,000 feet.
5:05 a.m.: The three form a loose V formation, Enola Gay leading, and at 205 m.p.h. and 9,200 feet, head toward Japan.
6:30 a.m.: Parsons completes arming the bomb; Tibbets informs crew they are carrying atomic weapon; Enola Gay begins climb to attack altitude.
7:09 a.m.: Air-raid warning sounds in Hiroshima as American scout plane Straight Flush approaches to check weather conditions.
7:25 a.m.: Straight Flush advises Enola Gay, now at 26,000 feet, that weather is clear; Tibbets informs his crew target will be Hiroshima.
7:31 a.m.: All-clear signal given in Hiroshima.
8:05 a.m.: With Enola Gay at 30,800 feet, Van Kirk announces they are 10 minutes from aiming point, Aioi Bridge.
8:12 a.m.: Van Kirk informs Tibbets they have reached initial point of bombing run.
8:13:30 a.m.: Tibbets declares, "It's yours," passing control of plane to bombardier Maj. Thomas Ferebee.
8:14 a.m.: Crew dons Polaroid goggles to protect their eyes.
8:15:17 a.m.: Bomb falls clear and Ferebee yells "Bomb away!" Enola Gay, at 328 m.p.h., begins steep power dive and right turn to escape blast.
8:16 a.m.: After a 5.5-mile drop, the bomb detonates 800 feet southeast of the Aioi Bridge. Explosive yield: 12,500 tons of TNT.
Atomic Delivery
The airplane that delivered the atomic bombs was the first intercontinental, pressurized bomber. It could lift its crew and load above 30,000 feet, out of range of most ground weapons and interceptors.
B-29 PROFILE
First prototype flight: Sept. 21, 1942
Weight: 70,000 pounds
Height: 27 feet, 9 inches
Required runway: 8,000 feet
Length: 99 feet
Internal power: 150 electric motors*
Propeller span: 16.5 feet
Top speed: 350 m.p.h.
Cruising speed: 220 m.p.h.
Range: 4,000 miles
Wingspan: 141 feet
Power: Four Wright 18-cylinder engines, 2,200 horsepower each
Protective weapons: 12 .50-caliber machine guns and one 20-millimeter cannon; all guns except 20-mm cannon in tall were removed from atomic bombers.
Inside the Bomb
The Hiroshima bomb used a set of switches to guide electrical current from batteries to a detonator. That explosive drove a small piece of uranium down a "gun barrel" and into a larger piece, achieving the volume necessary for explosion--critical mass. The sequence:
1. Bomb drops, closing first switch and initiating timer that holds all circuits open, allowing bomber to begin getaway.
2. After 15 seconds, timer closes second switch; current continues to another, controlled by height detector.
3. At 5,000 feet, next switch closes, allowing current to reach small radar set.
4. Radio waves from radar bounce off ground, reach bomb's antennae, closing final switch.
5. Conventional charge behind uranium bullet detonates, driving bullet into uranium target, causing explosion.
Length: 10 1/2 feet
Diameter: 29 inches
Weight: 9,700 pounds
A-Bomb in Context
How the atomic attack deaths compare to other notable bombing targets of World War II:
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