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Blog Topic: B-29 Escape Tactic, after dropping atom bomb

March 28, 2015

Illustration of B-29 bomber making escape turn after dropping the atom bomb.

play animation stop animation B-29 escape turn & power dive

This animation shows a B-29 Superfortress making a 155° escape turn, combined with a power dive, after dropping an atomic bomb. The bomb continues traveling forward, detonates at 1,800 feet. (Not drawn to scale). Animation by ©

In reading about the B-29 bombers involved in the atomic bomb missions of Hiroshima and Nagasaki, it became evident to me
that these missions were flown quite differently from any previous high level bomb runs of WW2. Once the B-29 bomber dropped the atomic bomb at 30,000 feet, it immediately went into a hard 155 degree turn while simultaneously diving.

Bombing with Conventional Weapons

American high level bombing missions with conventional weapons were typically at about 24,000 to 25,000 feet, and these bombers (often times a formation of airplanes) continued to fly straight forward or gradually turn to head back to base. There wasn't any special escape maneuver used since there was no danger of being caught in the bomb blasts. They just held formation after the bombs were dropped.

Low altitude bombing involved a danger from the blast, which could destroy the aircraft, but this was handled with a time delay on the bomb's fuse. So a low altitude bomber would come over and drop its bomb, which would impact on the target and detonate after the bomber was safely out of range.

Unique escape turn maneuver for B-29 carrying atom bomb

The 155 degree escape turn maneuver was unique to the B-29s on the atomic bomb missions. It was used to put the maximum distance between the airplane and the detonation of the bomb, whose shock wave was extreme and its mushroom cloud quickly boiled up 30,000 to 50,000 feet into the atmosphere. Containing dirt, dust, and debris at extremely elevated temperatures with a potential to actually ignite the airplane, we now also know that those clouds were also highly radioactive.

A B-29 bomber was traveling at approximately 300 miles per hour when it dropped the atomic bomb. The detonation point for the bomb was set at about 1800 feet above ground level to do maximum damage to the city and it took a about 45 seconds for the bomb to fall the 28,200 feet, down to the detonation point. That means the bomb traveled forward for 45 seconds, at close to 300 miles per hour. In that 45 seconds, the bomb traveled two and a quarter miles in the forward direction – the same direction that the bomber was moving when the bomb was dropped. The way to put maximum distance between your B-29 bomber and the the bomb's detonation point was to turn around and fly in the opposite direction.

So the bomber immediately went into an escape turn after dropping the atomic bomb. The act of turning slowed down the bomber, so a dive was needed to pick up speed again. When worked out mathematically, a 155 degree turn and dive to increase speed, would obtain the maximum distance between the bomber and the point of the detonation.

In practice runs they thought they could get almost 7 miles away from the detonation, using this turn/dive technique. Paul Tibbits, commander of the Enola Gay during the first atomic bomb mission, and commander of the composite group in charge of delivering these atomic bombs, thought that 7 miles was pretty good, and would be a safe distance. But the scientists at Los Alamos disabused him of that idea stating that they really could not determine a safe distance.

Concern over atom bomb blast destroying B-29 bomber

The detonation of the atom bomb was really going to create a huge explosion, and this was the reason for all the concern about the blast destroying the B-29 Superfortress bomber. To put this in perspective, a B-24 Liberator bomber with a full bomb load of conventional bombs, and standard gas loads for an average flight, would carry about 8 tons of bombs.The atom bomb was estimated to have nearly the energy equivalent to 20,000 tons of TNT, in a single explosion. So the atom bomb would be equivalent to the combined bomb loads of approximately 2,500 B-24 Liberator bombers, all detonating simultaneously at one point.

As it turned out, with the first bomb, which was dropped on Hiroshima, they did get approximately 6 to 7 miles away from the blast, following this procedure. On the second mission with Bock's Car, Major Sweeney, the pilot, was apparently distracted during the turn and continued a bit beyond the 155 degrees and somebody had to warn him that he was still turning. The planes received two heavy jolts. The first was a shock wave from the bomb's detonation and the second was the shock wave from the blast down into the ground's surface underneath the initial explosion, which was then reflected back up into the air.

So I found it very interesting to learn about this turn/dive escape maneuver for the B-29 bombers on the atom bomb missions. I also saw a nice illustration of this in a model display at Wendover Air Field in Utah, on a recent visit there, and will get the photos from that trip put up soon.

~ Jon

Reference and further reading
1Felt, Jonathan S., dir. Men Who Brought the Dawn: The Atomic Missions of Enola Gay and Bock's Car.
Greenwich Workshop, 1995. Documentary.


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