ATTACK ON HIROSHIMA : DROPPING THE BOMB

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:

*--*

DATE LOCATION DEATHS August-October, 1940* England 14,000-plus Aug. 23, 1942 Stalingrad 40,000 July 24-Aug. 2, 1943 Hamburg, Germany 50,000 Feb. 13, 1945 Dresden, Germany 35,000 March 3, 1945 Berlin 25,000 March 9-10, 1945 Tokyo 100,000-plus Aug. 6, 1945 Hiroshima, Japan 80,000** Aug. 9, 1945 Nagasaki, Japan 35,000**

*--*

* Includes London “blitz”

** Does not include later deaths from radiation

Atomic Arcana

* Americans received valuable weather data from a Chinese guerrilla leader: Mao Tse-tung.

* Nine Nagasaki shipbuilders, sent to work in Hiroshima, survived the Aug. 6 bombing, returned home and also survived the Aug. 9 bombing.

* It would take approximately 2,000 B-29s to carry enough conventional explosives to equal the blast at Hiroshima.

* 23 American POWs were killed in Hiroshima.

* The Enola Gay was 400 miles away from Hiroshima before the crew could no longer see the mushroom cloud.

* In 1945, the Gallup Poll reported that 85% of Americans endorsed the dropping of the A-bombs; today about 59% do so.

* Radar officer Lt. Jacob Beser was the only man to fly on both atomic strike planes.

* Enola Gay pilot Tibbets carried poison pills for his crew in case they were shot down.

What They Saw

The Hiroshima explosion created a cloud that has become a signature of nuclear destruction. Here’s how it happened:

A. With the flash of bluish-white and ultraviolet light, air is heated to about 18 million degrees. Resulting fireball creates a heat wave traveling at the speed of light (186,000 miles per second).

B. The following blast forms wall of pressure, moving about 2 miles per second. Part reflects off ground. When reflected wave catches up with the original, pressure doubles.

C. Pressure creates suction, drawing wind into blast area at up to 620 m.p.h.; fireball and hot gasses rise.

D. Fireball touches ground; dirt and other debris are sucked into the rising column, creating mushroom cloud.

On the Ground

More than a third of those who died were within 0.6 of a mile of the hypocenter--the point on the ground directly beneath the explosion. Ultimately, about a third of Hiroshima’s 320,000 residents would perish.

Hiroshima Toll

Killed: 37%

Slightly injured: 10%

Seriously injured: 15%

Not injured: 37%

Missing: 1%

*--*

% killed Buildings Miles from hypocenter or missing destroyed 0.6 85% 100% 1.2 48% 99% 1.8 7% 91% 2.4 1% 83% 3.0 1% 67%

*--*

Reflections

ALBERT EINSTEIN: Before World War II began, he wrote President Franklin D. Roosevelt a letter saying an nuclear bomb might be possible and urged that the government build one.

“I made one great mistake in my life--when I signed the letter to President Roosevelt recommending that an atomic bomb be made.”

****

PRESIDENT HARRY S. TRUMAN: Did not even know of the atomic project’s existence until he became President when Roosevelt died April 12, 1945. He made the decision to drop the bomb.

“The final decision of where and when to use the atomic bomb was up to me. Let there be no mistake about it. I regarded the bomb as a military weapon and never had any doubts that it should be used.”

****

BRIG. GEN. LESLIE GROVES: As a military engineer and deputy chief of construction for the U.S. Army, he built the Pentagon before assuming overall command of the atomic project.

“I considered it my duty to recommend that the bomb should be dropped. After all, great numbers of our boys were dying every day.”

****

J. ROBERT OPPENHEIMER: Physicist who led the team of scientists that built the bomb in a Los Alamos, N.M., laboratory. Resigned two months after the bombs were dropped.

“If atomic bombs are to be added as new weapons to the arsenals . . . of nations preparing for war, then the time will come when mankind will curse the names of Los Alamos and Hiroshima.”

****

COL. PAUL TIBBETS: Commander of the strike force assembled to drop the atomic bombs--the 509th Composite Group. He piloted the Enola Gay--the bomber named after his mother--on the first atomic mission.

“I had been expecting to see something big, but what is big? What I saw was of a magnitude and carried with it a connotation of destruction bigger than I had really imagined.”

Sources: World Book Encyclopedia; “Saga of the Superfortress,” by Steve Birdsall; “The Making of the Atomic Bomb,” by Richard Rhodes; “Enola Gay,” by Gordon Thomas and Max Morgan Witts; “Day One,” by Peter Wyden; “Fall of Japan,” by Keith Wheeler

Researched by TOM REINKEN / Los Angeles Times