Largest-yield nuke a B-29 could have delivered, safely?

I was just wondering…about what would have been the largest yield nuclear weapon that a B-29 bomber could have delivered, and still escaped the blast? Tens of kilotons? Hundreds? Megatons, even?

I know the Enola Gay made a big turn after dropping the 13kt “Little Boy,” to make sure it was safely out of harm’s way, but I don’t know if Bock’s Car did the same when dropping the bomb on Nagasaki. And I don’t know if the turn was necessary for dropping a nuke, or if it was just for the sake of being cautious, or if it could have been foregone with other changes to the attack plan. Can anyone enlighten me?

Well, thanks for your patience,
Ranchoth

Some of the early thermonuclear weapons were in the 10 MT range. The largest U.S. thermonuclear bomb was about 25 MT (B-41).

The trick to making these weapons survivable for the crew that dropped them was the addition of parachutes to the bomb. This gave the crew enough time to escape the area of the blast. A great deal of engineering went into designing parachutes that could quickly and gently slow down a very heavy bomb that was traveling at a high speed. Conventional parachutes were useless for this task.

Not directly answering the question asked, but perhaps relevant: I recall hearing as a child in the early 50s, when the B-52s were first coming on line, that the one bomber the U.S. had that was capable of delivering a thermonuclear bomb to the U.S.S.R. on a direct flight was the B-36.

The B-29s would probably have been quite capable of delivering H-bombs within their flight range, but they were not particularly long-range bombers as were later developments. (Remember that one major point to taking Iwo Jima was to have an airbase close enough for the B-29s to carry significant payload to bomb Japan.)

According to my copy of Volume 1 of the Nuclear Weapons Databook*, the B-29 was officially capable of delivering the Mk-III, Mk-IV, Mk-5, and Mk-6 bombs, in addition, of course, to the Little Boy and Fat Man devices. Except for LB (a gun-type weapon), all of these were implosion/fission bombs. The Mk-III was the first production model of the Fat Man. The maximum yield of the later ones was in the 40 Kt range, according to the Databook.

So much for the bombs the plane was officially rated to deliver. What was theoretically possible? The B-29 could carry a bomb load of 20,000 pounds, so it was theoretically capable (from a physical standpoint, at least) of carrying almost any of the nuclear weapons in the U.S. arsenal. (A notable exception: the Mk-17, the first droppable thermonuclear device, which weighed in at a whopping 21 tons, and had a yield “in the megaton range.” It was delivered by the B-36. The Databook has a really cool picture of this mammoth bomb.) So the B-29 might have been adapted to deliver the 8,850-lb B53 bomb, with a yield of 9 Mt. (Of course, you’d have to spring for the optional rack to hold it.) First deployed in 1962, the B53 was designed for the B-52 bomber, and the warhead version, the W53, was designed for the Titan II missile.

According to Enola Gay by Gordon Thomas and Max Witts, before they actually dropped the bomb, no one knew for sure how far away would be far enough. Col. Tibbets was concerned about damage to the plane from the blast and shockwave, and wanted to be at least seven miles from the aiming point when the bomb detonated. His 155-degree diving turn accomplished this. I’m guessing that continuing in a straight line would have put them closer at detonation, or he wouldn’t have bothered with the turn. FYI, the Hiroshima bomb was dropped from an altitude of 31,060 feet.

I don’t happen to know how far away from a 9 Mt blast one has to be to live to tell about it, but I’m guessing seven miles may not be quite far enough. Maybe with one of mks57’s parachutes you could put a few more miles between yourself and thermonuclear incineration. But all in all, I’d prefer to be speeding away from the scene in a jet, rather than the B-29, which had a top speed of 357 mph.

BTW, I’ll mention, just to make you jealous, that I’ve been in the cockpit of the Enola Gay, and sat in the bombardier’s and pilot’s seats. (I used to work for the National Air and Space Museum.)

  • Ranchoth, I think you should try to get your hands on a copy of this book. A) It’s fascinating in its own right, and 2) I’ve used it to answer a couple of your questions now.

Yes, *Bockscar * (no apostrophe) also made the same diving turn as Enola Gay.

For more information, see Decision at Nagasaki: the Mission that Almost Failed by Lt. Col. Fred Olivi, co-pilot of the Bockscar

The turn is necessary because due to the momentum of the bomb and plane, the bomb would basically be travelling at teh same speed as the plane, and therefore would detonate almost directly under it.
Not fun, I should think.

A B-29 travels at about 10 km/minute and the lethal radius (thermal effects) for a 9 MT weapon is about 29 km (Nuclear Weapons Effects Calculator). With a ribbon parachute, the time of fall for the first thermonuclear weapons was about 200 seconds (A Hindenburg in the Bomb Bay, Chuck Hansen).

I remember reading that one of the reasons for the bare aluminum on the fuselage of the B-29/36 was thermal effects from nuclear weapons. They didn’t want anything that would absorb heat and burn, like paint.

Many nuclear weapons had a lay-down fusing option, where the weapon would be retarded by a parachute, land on the ground, and detonate after a programmed delay, giving the flight crew extra time to leave the area.

[nitpick]It was P-51s that were based on Iwo Jima, allowing the B-29s to have fighter escort all the way to their targets. Iwo Jima also provided a closer point for emergency landings of crippled bombers. But I don’t believe the bombers themselves were based there.

THe obvious question is: What about bursts from x-rays and other particles? How dangerous to the crew in an airplane above the blast? (And what other particles would one worry about–gamma rays? Not sure.)

Ummm, no. The plane was called Bock’s Car: two words, with apostrophe, because the pilot was Captain Frederick Bock.

If you’re basing the claim on the fact that the nose art doesn’t have an apostrophe and seems to run the two words together, I don’t accept that artistic choice as an authority for the plane’s actual name. And neither do most scholarly writers I’ve consulted, e.g. Thomas and Witt (mentioned above), Richard Rhodes (The Making of the Atomic Bomb), Peter Wyden (Day One), to name a few.

X-rays and gamma rays have a relatively short range in comparison to the blast and thermal effects. For a 9 MT device, the 500 rem dose radius is about 4.7 km. Some devices are designed to produce large numbers of neutrons, like the so-called neutron bomb. As device yield scales up, thermal effects represent an increasing share of the device’s total energy output.

Someone else will have to confirm this, but I remember being told that planes would make a steep climb before releasing the bombs. This would give the plane more time to get away as the bomb traveled upwards for a distantance and then fell.

A little OT, but if ever in Albuquerque, drop into the Atomic Museum. They have a whole lot of the nuclear bombs, warheads, missles, cruise missles, etc. from the US arsenal. An F-105 on a pylon, a B-52 with one of the very large thermonuclear devices under it. A great display if you like this sort of thing.

The Air Force developed a flight maneuver that “tossed” the bomb towards the target in an upward arcing trajectory. The aircraft would immediately reverse course after weapons release. I believe this was done to make low-altitude bombing runs survivable. One of the pilots wrote an account of his experiences with the training for this maneuver in Air & Space Smithsonian magazine IIRC.

Standard delivery method for small jets is a high loft maneuver. Basically it’s an Immelman, with the weapon released on the upward portion of the turn. No idea if the B-29 is capable of this maneuver.

Nuclear Weapons in the Strategic Air Command and the Nuclear Weapons Archive say that the Mk-5 could be configured up to a 120kt yield, and the Mk-6 to a 160 Kt yield. (I don’t know if they were using tritium-deuterium boosting to do this, or something else.) With 160 kt blast’s lethal radius of 5.5 kms, and by mks57’s figures, this would seem to fit well within a safe margin to drop from a B-29.

Consider me burning with more jealousy than a thousand suns. :cool:

I think you’ve sold me! I’m going to take a look for it after payday. Thanks!

That was the LABS (Low Altitude Bombing System). The link mentions how it could have been used on an A-1 Skyraider on a nuclear mission (!). There was also another method called “Over the Shoulder” which drops the weapon from a more straightforward “loop” rather than an Immelman. (I don’t know how “popular” a method this was, compared to the LABS.)

And there does seem to be confusion over whether or not the B-29 that attacked Nagasaki is properly named Bockscar, Bock’s Car or Bocks Car. The photograph of the nose doesn’t have an apostrophe, and it may or may not have a space in it. I guess only Capt. Bock could tell us, for sure. :smiley:

And thanks again for all the help, everyone! I knew I could count on you guys. I salute ye!

It seems pretty clear to me that it’s “Bocks Car”. There is no apostrophe and there is a space between the “s” and “c”. If you look close, you’ll see that the “s” and “c” don’t overlap while all the other letters do.

I’m basing it on the words of Fred Olivi, who actually flew the dang thing and was actually there. In his book it’s always Bockscar, and while the Lt. Col is deceased now he did live most of his life in this area where I live currently and thus was well known to many in the aviation crowd around here. Everyone I’ve spoken to who knew Olivi personally has told me that he always referred to it as Bockscar, no apostrophe. So, apparently, the guys who worked on and flew the thing always left off the apostrophe.

In other words, no, I’m not basing it on the nose art at all.

And it occurs to me that the whole debate about how to spell the name of the airplane might be of more concern to scholars and nitpickers than it ever was to either the flight crews or Captain Bock.

If the bomb was parachuted down, would there be any chance of anti-aircraft fire striking it? I often wondered about that when I read reports of the US using those “daisy cutter” devices in Afghanistan.