What was the plan if the Hiroshima and Nagasaki bombers were attacked?

My understanding is that Japan didn’t try to shoot them down because they didn’t think a single bomber was going to do anything. But did they have a plan if they got shot at or intercepted by fighters? Would the bombs have gone off if they crashed?

For months, USA had been sending a single bombers to drop a single bomb. They were intercepted at first. With Japan’s fuel shortage, Japan usually stopped scrambling a squadron of aircraft to 31,000 feet to stop a lone bomber. (It probably would have taken 20 minutes at full throttle to get that high)

I don’t know what provisions were made should Japan have intercepted the Enola Gay.

That’s very interesting.

Just to be clear, was the US doing this with the goal of lulling the Japanese into ‘tolerating’ such sorties to set the stage for Enola Gay* to fly in unopposed?

*or whatever plane was eventually used

I suspect that the plan was to make the Japanese spend a lot of fuel, and risk only a few bombers. The Japanese decided not to play. Then the possibilities changed.

Tris

Cite?

I don’t know about bombing missions, but the U.S. had been sending single B-29s outfitted as reconnaissance planes over Japan beginning in November 1944. The planes flew too high for Japanese defenses, so there was no real need to send more than one on a mission.

The 509th Composite Group (which dropped the bomb on Hiroshima) had multiple practice missions beforehand.

“In late May, the 509th was moved to Tinian Island, where they operated combat missions starting June 30, 1945. They dropped bombs on Japanese-controlled islands throughout July to practice radar and visual bombing procedures, in addition to dropping pumpkin bombs in Japan, and practicing missions with inert Little Boy and Fat Man prototypes.”

According to the cite, neither the Hiroshima nor Nagasaki attacks were made by a “single bomber.” Enola Gay was accompanied by two other B-29s as observers, and Bock’s car was accompanied by three. Of course, only one plane carried a bomb.

From places like Hershey’s book, the folk in Hiroshima assumed the single bomber was a weather recon flight. These were quite common. There’d often not even be an air raid alert issued in these cases.

While there were other bombers in the group, some distance was maintained at the time of the bombing for added safety. Remember, the bombing aircraft had to dive and turn to get to a more favorable position for the blast. No point in putting the other bombers into the same danger so they could be further away and higher. A person on the ground might have only seen the one bomber.

The post asking for a cite referred to the statement that pre-Hiroshima flights were conducted by a single bomber. Practice missions (i.e. by “The Great Artiste”) may have involved just one bomber carrying out a raid on Japanese targets (it’s unclear to me whether the entire mini-group that eventually bombed Hiroshima went out on these practice missions, or just one bomber at times).

To address the last part of this question - the answer is mostly no. If the plane was shot down, the bomb would almost certainly NOT have exploded with a nuclear detonation. It’s possible that the conventional explosives would have gone off in an uncontrolled manner, resulting in either a conventional explosion spreading radioactive material (a dirty bomb) or a fizzle (partial nuclear detonation). But the odds of the plane being shot down resulting in a full nuclear detonation are tiny at best. Getting a nuclear weapon to detonate properly is very difficult and requires extremely precise timing - something that typically doesn’t occur during a plane crash.

This is correct except in the case of the “Little Boy” Hiroshima device. That was a gun-type device with limited safety interlocks. It was considered so risky that that a high likelihood existed for a nuclear detonation in the event of a crash.

For this reason the weapons officer Deak Parsons unilaterally and without informing General Groves made the decision to not load the bomb with cordite explosives until after takeoff. Source: “Racing for the Bomb”, by Robert S. Norris.

Little Boy probably would have caused a pretty substantial fizzle- it wasn’t terribly safe, being a very redundant gun-type weapon.

But yeah, the Japanese weren’t afraid of a handful of bombers at high altitude in daytime; most of the really destructive raids until then had been hundreds of bombers at low level at night.

As mentioned the 509th Composite dropped a number of large conventional bombs similar in size to the ‘Fat Man’ type A-bomb on Japan (called ‘pumpkin bombs’) in the few weeks prior to the nuclear attacks.
https://en.wikipedia.org/wiki/Pumpkin_bomb
More specifically Mann in “The B-29 Superfortress-A Comprehensive Registry…” says 18 such missions from July 20 of which details are given of 16 missions totaling 51 sorties with no losses. According to Polmar’s “Enola Gay” Japanese fighters were spotted on at least a few of these missions but didn’t intercept.

But the common knowledge aspect is that F-13’s (recon B-29’s, less confusingly designated RB-29’s by the time of the Korean War) and other special mission B-29’s flew alone or in small groups over Japan from late 1944, even in daylight. B-29’s constrained to formation speeds, at first near 30k ft, but later daylight bombing altitude was low 20’s, were not that difficult to intercept. Lone a/c able to go full speed and fly as high as they were able were difficult targets. This Japanese list which correlates B-29 losses over Japan by tail number with causes gives one F-13 possibly downed by fighters but no details, it just disappeared per US reports, 42-93863 Feb 14 1945
http://aomorikuushuu.jpn.org/mia.html

Even obvious day bombing raids were often not intercepted by summer 1945, as the Japanese day fighter force conserved fuel for the expected invasion. And B-29’s did conduct conventional bombing raids in daylight as well as night in that period. To get an idea of scale of fighter opposition same list credits 3 B-29’s to fighters June 6, 2 by a/c of the Akeno Fighter School in a raid on Mitsubishi a/c factory near Kobe. One by JNAF 302nd Air Group on June 10, 2 on June 22 (info is probably from US reports since no specific Japanese fighter units are given), and the last two in daylight on June 26 (again seems to be US info for one, the other just disappeared per US reports). After that a handful of B-29’s were downed by Japanese night fighters, the last being 44-86344 by JAAF 18th Sentai Aug 2 (unknown cause in US reports). The combat loss rate of B-29’s was quite low by WWII standards by spring-summer '45 and as the list shows most direct combat losses were to AA fire.

The obvious inference from the mission planning of 509th Composite Group was that the threat from Japanese fighters to small numbers of B-29’s at ~30k ft was basically dismissed. The Silverplate’ A-bomb capable B-29’s were also faster than standard ones, though in part from removal of defensive armament except the tail guns which meant ‘what to do’ in case of successful interception would seem to have been ‘run, and try to keep the enemy fighters within the field of fire of the tail guns’. I’ve never come across a specific discussion of the risk assessment though as from a primary source.

From The Making of the Atomic Bomb by Richard Rhodes:

From Wiki:

Great thread, thanks for the good info folks.

This idea of a B-29 being capable of high and fast flight, therefore not easy to intercept, seems the model for bomb delivery going into the cold war. No doubt this contributed heavily to very high speed interceptor fighter development.

(There is another contemporary thread asking why a fighter would need to be able to fly Mach 2, and the thread does give interception as a reason. But now, nukes are delivered by missiles, hence fast bombers / faster interceptors idea is obsolete. As are Nike missile sites around major cities. Interesting to visit, if you can find one.)

The 509th’s bombers were all the “Silverplate” variant, with all guns removed except for the tail turret to reduce weight and drag. If a Japanese fighter could have reached them, they’d be defenseless.

Except you know, by that time, the Japanese didnt have much in the way of fast, high altitude fighters.

https://en.wikipedia.org/wiki/Air_raids_on_Japan#Air_defenses
*
Japan’s air defenses were unable to stop the Allied air attacks.[203] Owing to the short range of the country’s land-based radar, and Allied attacks on IJN picket ships, the defenders typically had only about an hour to respond to incoming B-29s once they had been detected. Japanese signals intelligence units could provide longer warning times of incoming raids by eavesdropping on the bombers’ radio communications, but were unable to predict the target of the attack. As a result, fighter units did not have enough time to scramble and reach the bombers’ cruising altitude before they arrived over their target, and most raids were intercepted by only small numbers of aircraft. Moreover, the American bombers were capable of flying faster at high altitude than many Japanese fighters.[204] Even when the fighters managed to close within gun range, the well-built B-29s were often able to sustain large amounts of damage. Due to the difficulty of intercepting and downing B-29s, the Japanese fighter pilots increasingly perceived their efforts as being futile.[139] From August 1944 Japanese aircraft occasionally conducted suicide ramming attacks on B-29s, and several specialized kamikaze fighter units were established in October; by the end of the war, ramming tactics had destroyed nine B-29s and damaged another 13 for the loss of 21 fighters.[205]…During the last weeks of the war Superfortresses were able to operate with near impunity owing to the weakness of the Japanese air defenses; LeMay later claimed that during this period “it was safer to fly a combat mission over Japan than it was to fly a B-29 training mission back in the United States”.[213]

Overall, Japanese fighters shot down 74 B-29s, anti-aircraft guns accounted for a further 54, and 19 were downed by a combination of anti-aircraft guns and fighters. IJAAF and IJN losses during the defense of Japan were 1,450 aircraft in combat and another 2,750 to other causes.[214]*

Note this-During the last weeks of the war Superfortresses were able to operate with near impunity owing to the weakness of the Japanese air defenses; LeMay later claimed that during this period "it was safer to fly a combat mission over Japan than it was to fly a B-29 training mission back in the United States"
There was almost no danger.

and to add to what was said earlier: Four days later the 509th Composite Group’s modified “Silverplate” B-29s began flying practice raids against Japanese cities, each armed with a single high-explosive “pumpkin” bomb; further practice missions took place on 24, 26 and 29 July. Japanese fighters did not attempt to intercept these aircraft, and their bombing altitude of 30,000 feet (9,100 m) was beyond the range of most anti-aircraft guns

Except that rear turret.

Also known as a tail turret, as stated in that quote.

Nobody said Japan *had *high-altitude interceptors then, either. That lack is what made Silverplate safe.