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Deaf Smith
08-15-2010, 08:50 PM
http://www.upa.pdx.edu/IMS/currentprojects/TAHv3/Content/PDFs/Operation_Downfall.pdf

Yes gas, poison gas, to get the Japanese defenders that would have been dug in all over Japan if we had invaded.

This and Gen. Marshals idea of using atomic bombs to clear the beach heads would have made even the bloodbath that would have happened even worse.

It’s a very interesting read.

Deaf

Wizard
08-16-2010, 12:23 AM
http://www.upa.pdx.edu/IMS/currentprojects/TAHv3/Content/PDFs/Operation_Downfall.pdf

Yes gas, poison gas, to get the Japanese defenders that would have been dug in all over Japan if we had invaded.

This and Gen. Marshals idea of using atomic bombs to clear the beach heads would have made even the bloodbath that would have happened even worse.

It’s a very interesting read.

Deaf

It's just my opinion, but I doubt very seriously that poison gas, especially during the monsoon season, would have been all that effective. US forces in the Pacific had precious little experience in the widespread use of poison gas under any circumstances.

Nor, I suspect, would atomic weapons have had much effect in the tactical role; especially since almost all the Japanese troops would have been dug in, in prepared fortifications, in particularly mountainous terrain that is characteristic of southern Kyushu.

I think the fighting on Kyushu would have much more closely resembled that of Okinawa than the campaign on Luzon. The kamikazes would have most likely been much more effective than on Okinawa, if only because so many of the novice pilots that were lost on the long overwater flight to Okinawa, would actually be more likely to strike their targets near Kyushu. There would be no way to deploy radar picket ships to give warning of kamikaze attacks as at Okinawa.

Again, just my opinion.

Deaf Smith
08-16-2010, 08:06 PM
I think the monsoon season in Japan is not in November Wizard.

As for A-bombs, I sure hope Gen. Marshal was not thinking ground detonations, as talk about dirty bombs. But who knows, he might considering that is what would be needed to get to the caves. An earthquake.

Deaf

Wizard
08-16-2010, 09:22 PM
I think the monsoon season in Japan is not in November Wizard.

I was thinking about Operation Coronet.


As for A-bombs, I sure hope Gen. Marshal was not thinking ground detonations, as talk about dirty bombs. But who knows, he might considering that is what would be needed to get to the caves. An earthquake.

Deaf

I don't know the details of how the atom bombs might have been used in a tactical role in either the Kyushu or the Kanto Plain operation. An air-burst detonation would make little sense since it would only affect troops out in the open, which surely would be a small minority of the Japanese defenders. Even bunkers with moderate overhead protection would protect all but those in very close proximity to ground zero.

Conversely, a ground-level detonation would have a much smaller effective area and the effects would be restricted by terrain features on anything but a completely flat plain. Only those caves or fortifications in very close proximity (a matter of a few hundred yards) to ground zero would be likely to be collapsed by a ground detonation. To produce even moderate ground tremors, an atomic explosion would have to be deep underground, something I don't think the Allies had the technology to accomplish in 1945.

Uyraell
08-17-2010, 01:55 AM
The Allies certainly had the technology to accomplish deep-ground detonation in 1945.
Grand Slam.
One of those casings with a nuclear payload would, I suggest, provide a more than adequate subterranean detonation and explosion.

The wisdom of doing such a thing: I call into question.

The feasibility thereof: I have no doubts.

Kind and Respectful Regards my friends, Uyraell.

Wizard
08-17-2010, 03:06 AM
The Allies certainly had the technology to accomplish deep-ground detonation in 1945.
Grand Slam.
One of those casings with a nuclear payload would, I suggest, provide a more than adequate subterranean detonation and explosion.

The wisdom of doing such a thing: I call into question.

The feasibility thereof: I have no doubts.

Kind and Respectful Regards my friends, Uyraell.

I'm not so sure that the mechanism of an atomic bomb, which was quite different and quite a bit more complex than the explosive and fuse in a grand slam bomb, would survive the tremendous impact necessary to bury it deep enough, especially in rocky terrain, to achieve the desired effect.

The Grand Slam bomb was designed to undermine the foundations of buildings, bridge piers, and heavy fortifications by creating a crater or cavity underneath, or very near, those foundations, resulting in their collapse. This really wouldn't be of much help in knocking out caves and other underground fortifications that typified Japanese defenses, some of which extend a hundred feet or more underground and featured reinforced concrete shoring and blast shields.

A nuclear blast might destroy cave entrances if they were within a few hundred yards of the detonation point, but the Japanese typically connected their caves and firing points with numerous tunnels having a dozen or more entrances. It would, in effect, be using atomic bombs to destroy a handful of bunkers and cave entrances, while leaving the underground portions of the fortification complex intact. The US would have had only a dozen or so nuclear devices, and to use them successfully in a tactical role they would have to guarantee knocking out entire fortification complexes over a wide area of several miles at least.

It's my opinion that in the mountainous terrain, with bedrock very near the surface, of southern Kyushu, atomic weapons wouldn't be effective in destroying significant portions of the Japanese underground fortifications.

Uyraell
08-17-2010, 03:42 AM
The terrain of deployment is a highly relevant factor, I agree there, Wizard.
The fusing issues with an atomic bomb are somewhat less complex than might be thought.

We are long accustomed to the knowledge that both A-bombs as dropped were "air-burst" weapons, detonating 60 or 80 feet above ground, and that they did so reliably.
But, that same accustomisation to the above information tends by it's own nature to blind us to the secondary characteristics of both A-bomb fuses: they could detonate at impact if necessary.

I'd respectfully suggest that since that is so, then it would not have taken much to reinforce the ground-impact detonation system to survive impact and cratering for long enough to be effective, thus detonating the now below-ground A-bomb.

As I said above, I agree the terrain is a highly relevant factor, but then too it was equally relevant at Beilefeld, and at the V2/A4 dome in France.
Both areas are cross-grained with ridges, and both would focus much of an atomic blast upwards to the atmosphere, yet I'd think there'd be sufficient of the blast having an effect to be terrifying even so.
And the Grand Slam was successfully dropped at each site.

Kind and Respectful Regards Wizard my friend, Uyraell.

Wizard
08-17-2010, 02:48 PM
The terrain of deployment is a highly relevant factor, I agree there, Wizard.
The fusing issues with an atomic bomb are somewhat less complex than might be thought.

I can't agree with this.

Both atomic bombs which were actually used on Japan were quite complex in their arrangement, and the detonating fuse for the chemical explosive was probably the simplest part of their mechanism. The bomb used at Hiroshima relied on bringing together two small (a few pounds each) masses of fissile material to form a critical mass. The "gun type" bomb did this by using essentially a gun barrel to fire one mass into the center of another mass thus achieving a mass of critical proportions.

The "implosion type" bomb, used at Nagasaki, was more sophisticated and used a very complicated layer of chemical explosives wrapped around a hollow sphere of plutonium to crush or "implode" the sphere into a tightly packed density of critical mass. In either case, if the body of the bomb were deformed in the slightest, as often happened on ground impact, it was highly likely that the internal mechanism for achieving critical mass might be impaired. Such impairment would almost certainly cause the bomb not to work, or to work in an inefficient manner, causing a low grade detonation of greatly lessened power.

For example, the precise arrangement of the chemical explosive in the implosion bomb was crucial because the shock wave of the explosion front had to be symmetrical and arrive at the fissile core at precisely the same instant over the entire surface of the core. Just the slightest variation in the way the chemical explosive detonated, or it's physical shape upon detonation, would throw the symmetry of the shock wave off sufficiently to cause failure of the bomb. In the gun type bomb, the slightest warping of the gun barrel would be sufficient to cause the projectile mass to be slowed down and cause only a partial explosion in the critical mass, seriously degrading the yield of the bomb.

With bombs relying exclusively on detonation of a mass of chemical explosive (i.e.the grand slam bomb), deformation of the body of the bomb does not matter as long as the fuse works while remaining in substantial contact with the explosive mass.


We are long accustomed to the knowledge that both A-bombs as dropped were "air-burst" weapons, detonating 60 or 80 feet above ground, and that they did so reliably.

Actually, the Hiroshima bomb detonated in an air burst at the altitude of 1,900 feet. The Nagasaki bomb detonated in an air burst at 1,650 feet.


But, that same accustomisation to the above information tends by it's own nature to blind us to the secondary characteristics of both A-bomb fuses: they could detonate at impact if necessary.

Both atomic bombs used on Japan, had radar altimeter fuses and barometric pressure fuses to produce an air burst. The necessary radar antennas were attached to the bomb's tailfin assembly. There was an impact fuse in each bomb, but it was strictly a back-up fuse; if the atomic bomb detonated at ground level, the scientists all felt that much of it's power would be dissipated in digging a crater.


I'd respectfully suggest that since that is so, then it would not have taken much to reinforce the ground-impact detonation system to survive impact and cratering for long enough to be effective, thus detonating the now below-ground A-bomb.

It's not the actual fuses or fusing systems that I'm referring to, but the bodies of the bombs themselves. Unlike chemical explosives which can be highly deformed and still be effective as long as they remain in contact with their fuses, the atomic bombs rely on the separate parts of the internal mechanisms of the bombs remaining in exact relationship to each other in order to function as designed. No matter how hardened the external bomb case, extreme impacts of the sort required to dig a grand slam bomb in deep enough into the earth to be effective, are almost certain to slightly warp or distort the position of the internal parts of an atomic bomb. The explosive "lens" of an implosion type bomb, if only slightly distorted, will explode, but will not produce the precision in the explosive wave front required to properly compress the fissile material and achieve critical mass.


As I said above, I agree the terrain is a highly relevant factor, but then too it was equally relevant at Beilefeld, and at the V2/A4 dome in France. Both areas are cross-grained with ridges, and both would focus much of an atomic blast upwards to the atmosphere, yet I'd think there'd be sufficient of the blast having an effect to be terrifying even so. And the Grand Slam was successfully dropped at each site.

Kind and Respectful Regards Wizard my friend, Uyraell.

I have no doubt that any atomic bomb detonated in any terrain, at any altitude, would be terrifying to anyone nearby who witnessed it, but the question really is, how many dug in and protected defenders would it kill or permanently incapacitate, and over what area would such an explosion destroy underground fortifications to the extent that they would be of no use in repelling an invasion?

I'm not at all convinced that comparing the success of the grand slam bomb in destroying missile storage/launch facilities in Europe is useful in determining the probability that an atomic bomb would be equally successful in destroying deep underground fortifications in Japan.

Best regards,
Wizard

Deaf Smith
08-17-2010, 07:37 PM
Well guys, I'm sure the RAF could have got 1000 Lancasters to pattern bomb the invasion beaches with Grand Slams. Now THAT would have taken care of the caves!

In fact, I wish at Iwo Jima they had done just that using B-29s to carry the Grand Slams and maybe have stopped alot of them from using the caves.

Happly, the Japanese surrendered and we didn't have to try moving soldiers over radioactive ground or firing mustard gas shells into caves (for you see that is how they would have delivered the gas, with shells.)

Deaf

Rising Sun*
08-17-2010, 08:13 PM
I have no doubt that any atomic bomb detonated in any terrain, at any altitude, would be terrifying to anyone nearby who witnessed it, but the question really is, how many dug in and protected defenders would it kill or permanently incapacitate, and over what area would such an explosion destroy underground fortifications to the extent that they would be of no use in repelling an invasion?

Rounded death rates for Hiroshima were:
- within 500 metres of hypocentre - 90% on day of detonation; 98% total
- 500 to 1000 metres of hypocentre - 59% on day of detonation; 90% total
- 1000 to 1500 metres of hypocentre - 20% on day of detonation; 45% total
- 1500 to 2000 metres of hypocentre - 11% on day of detonation; 23% total
- Average 0 to 2000 metres of hypocentre - 37% on day of detonation; 56% total
http://www.hiroshimacommittee.org/Facts_NagasakiAndHiroshimaBombing.htm

From that we can infer that about 90% of troops above ground within 500 metres of the hypocentre would be killed on the day of detonation, and the rest wouldn't be likely to be able to put up much resistance. About 60% between 500 and 1000 metres would be killed, with perhaps a small proportion of survivors able to put up effective resistance. For practical purposes, given the enormous reduction in defenders within a radius of about 1000 metres of the hypocentre, it would be a relative walkover for the vastly more numerous attackers, subject to what is said later about them being at risk of radiation sickness.

So, if the weapon is detonated in the middle of a two kilometre front where the enemy has concentrated his troops, the attacker gets a huge advantage from it. However, one would need to know the disposition of defenders to know whether that would have been likely. Given the opportunities for wide fronts and defence in depth, the Japanese may not have had any or many choke points where an atomic bomb would have conferred such an advantage on the Allies.

I have no idea what the effect of being in a weapon pit up to deep in a cave would have in reducing casualty rates. There might be some indication here, from the shielding effects of buildings.
http://www.rerf.or.jp/cgi-bin/frame.cgi?home=ds86a&page=Chapter7

Against any sheilding effect is the consequence of coming out of caves to fight and the constant exposure anyone in a weapon pit or, presumably, cave mouth would experience following the detonation:


Anyone staying within 1 kilometer of the hypocentre within 100 hours of the explosion was seriously affected by external exposure to gamma rays of induced radiation; therefore, those who were not exposed to the initial radiation but entered the city to aid victims or search for relatives and those who lived in the range of radio*active contamination were affected by residual radiation.
http://www.hiroshimacommittee.org/Facts_NagasakiAndHiroshimaBombing.htm

Allied troops entering the area would also be subject to the same risk and reduction in efficiency, and probably a greater reduction in efficiency than the enemy as they need to engage in vigorous exertion while the enemy sits in static positions. The longer the sick enemy delays the attackers, the sicker and less efficient the attackers become.

I have some recollection that there was to be a delay between detonation and moving Allied troops into the area but I can't recall what it was, assuming I'm correct in thinking there was to be a delay. The knowledge about radiation effects was pretty primitive at the time so it would have been a somewhat arbitrary figure.

Tactical use of atomic weapons would have produced a tactical dilemma for the Japanese. By the time the Allies were invading the Japanese would have been well aware of the effects of radiation, but with no understanding of what reduction might be caused by weapon pits, bunkers, caves etc. A commander would be faced with the choice of hoping that sufficient troops at the detonation site survived in fighting condition to present an effective defence or reinforcing with fresh troops who would then succumb to radiation sickness and become less effective. The better choice would be to use the fresh troops in an uncontaminated area, but this then means that the defender is no longer fighting on the ground and from the fortifications of first choice and has limited time and resources to construct fortifications and move men and materiel into the new defensive position. This significantly improves the attacker’s ability to overwhelm the defences with fewer casualties. Assuming, of course, that the attacking forces have not moved through the detonation site and acquired radiation sickness, in which case they will be of reduced efficiency which may cancel out any disadvantage the defender suffers by having to create quickly a new defensive position.

Wizard
08-18-2010, 12:37 AM
Rounded death rates for Hiroshima were:
- within 500 metres of hypocentre - 90% on day of detonation; 98% total
- 500 to 1000 metres of hypocentre - 59% on day of detonation; 90% total
- 1000 to 1500 metres of hypocentre - 20% on day of detonation; 45% total
- 1500 to 2000 metres of hypocentre - 11% on day of detonation; 23% total
- Average 0 to 2000 metres of hypocentre - 37% on day of detonation; 56% total
http://www.hiroshimacommittee.org/Facts_NagasakiAndHiroshimaBombing.htm

From that we can infer that about 90% of troops above ground within 500 metres of the hypocentre would be killed on the day of detonation, and the rest wouldn't be likely to be able to put up much resistance. About 60% between 500 and 1000 metres would be killed, with perhaps a small proportion of survivors able to put up effective resistance. For practical purposes, given the enormous reduction in defenders within a radius of about 1000 metres of the hypocentre, it would be a relative walkover for the vastly more numerous attackers, subject to what is said later about them being at risk of radiation sickness.

So, if the weapon is detonated in the middle of a two kilometre front where the enemy has concentrated his troops, the attacker gets a huge advantage from it. However, one would need to know the disposition of defenders to know whether that would have been likely. Given the opportunities for wide fronts and defence in depth, the Japanese may not have had any or many choke points where an atomic bomb would have conferred such an advantage on the Allies.

I have no idea what the effect of being in a weapon pit up to deep in a cave would have in reducing casualty rates. There might be some indication here, from the shielding effects of buildings.
http://www.rerf.or.jp/cgi-bin/frame.cgi?home=ds86a&page=Chapter7

Against any sheilding effect is the consequence of coming out of caves to fight and the constant exposure anyone in a weapon pit or, presumably, cave mouth would experience following the detonation:


http://www.hiroshimacommittee.org/Facts_NagasakiAndHiroshimaBombing.htm

Allied troops entering the area would also be subject to the same risk and reduction in efficiency, and probably a greater reduction in efficiency than the enemy as they need to engage in vigorous exertion while the enemy sits in static positions. The longer the sick enemy delays the attackers, the sicker and less efficient the attackers become.

I have some recollection that there was to be a delay between detonation and moving Allied troops into the area but I can't recall what it was, assuming I'm correct in thinking there was to be a delay. The knowledge about radiation effects was pretty primitive at the time so it would have been a somewhat arbitrary figure.

Tactical use of atomic weapons would have produced a tactical dilemma for the Japanese. By the time the Allies were invading the Japanese would have been well aware of the effects of radiation, but with no understanding of what reduction might be caused by weapon pits, bunkers, caves etc. A commander would be faced with the choice of hoping that sufficient troops at the detonation site survived in fighting condition to present an effective defence or reinforcing with fresh troops who would then succumb to radiation sickness and become less effective. The better choice would be to use the fresh troops in an uncontaminated area, but this then means that the defender is no longer fighting on the ground and from the fortifications of first choice and has limited time and resources to construct fortifications and move men and materiel into the new defensive position. This significantly improves the attacker’s ability to overwhelm the defences with fewer casualties. Assuming, of course, that the attacking forces have not moved through the detonation site and acquired radiation sickness, in which case they will be of reduced efficiency which may cancel out any disadvantage the defender suffers by having to create quickly a new defensive position.

The caveat here is that the above casualty figures correlated with the distance from the hypocenter (ground zero) applies only to the defenders who might be caught above ground and out in the open. As on Iwo Jima and Okinawa, most of the defenders would be underground or at least protected from blast, heat, and the worst of the radiation unless the attack happened to somehow catch them off guard and above ground. At most, probably only a few hundreds would be directly affected by the atomic bombs.

That doesn't bode well for the effectiveness of tactical nukes. In fact, it would appear that a tactical atomic bomb would mostly effect the civilian population of the area under attack. The Japanese military had no plans to evacuate civilians on Kyushu, but were going to use them as support troops. Given the nature of Japanese defensive fortifications in the latter part of the war, I would opine that tactical use of atomic bombs would turn out to be a massive waste of valuable resources.

My recollection is that the Manhattan Project scientists had advised waiting 48 hours before allowing American troops into an area where a nuclear device had been used. We now know this would have led to significant American casualties from radiation exposure. Only those Japanese troops who had been caught above ground at the time of the explosion, or who subsequently ventured out in the open, would be exposed to serious radiation; even a few feet of soil or rock overhead would protect against serious radiation exposure.

Do you have a source that indicates gas would be introduced into the underground fortifications by use of artillery shells? Or are you just surmising that would be the method? It doesn't seem to be a very effective way of using poison gas. On Iwo Jima, I believe, the plan was to lay down a gas barrage on the surface of the island, and then land specially trained troops who would pump gas into the fortifications through the ventilation openings. The Japanese would counter, of course, with gas masks and protective clothing, which probably would become less effective as the gas concentration became increased with time.

It was Roosevelt who vetoed the use of gas on Iwo Jima out of concern for world public opinion.

Uyraell
08-18-2010, 12:51 AM
Wizard, I apologise for having given inaccurate altitudes of detonation for both A-bombs.

I did read Leslie Grove's very informative tome some years ago, and yes, I'm reasonably familiar with the detonation mechanisms in each case.

My point with regard to the Grand Slam casing is that it was designed to survive impact without distorting (It was, in effect, battleship armour,).
The way I thought about it was: put a nuclear payload in a non-distorting casing, and one then has a very useful though admittedly dangerous weapon, capable of either digging out the defenders, or rendering them neutralised in place.

That the Grand Slam was successfully employed with a conventional payload suggested to me that it might be successful with a nuclear payload.

In short, the "dig-down" at impact for which Grand Slam was designed would be considerably augmented by the nuclear payload. That detonating such a payload underground in such a manner would be less efficient in causing casualty rates I do not debate: the point is plain enough.
However: the purpose of a nuclear payload Grand Slam would not be `a-priori to cause casualties directly.
The purpose would be to cause cave-in, implosion of the caverns/hollow spaces/caves nearby, and thus render the occupants unable to successfully defend against an incoming attack.
Accordingly, my thought was that the "loss of efficiency" in terms of over-all casualties as a result of detonation would have been accepted, as part of the price of what would amount (imho) to super-efficiency in the undermining/cave-in/implosion of cavern-spaces role.

Kind and Respectful regards Wizard my friend, Uyraell.

Rising Sun*
08-18-2010, 06:28 AM
Do you have a source that indicates gas would be introduced into the underground fortifications by use of artillery shells? Or are you just surmising that would be the method? It doesn't seem to be a very effective way of using poison gas. On Iwo Jima, I believe, the plan was to lay down a gas barrage on the surface of the island, and then land specially trained troops who would pump gas into the fortifications through the ventilation openings. The Japanese would counter, of course, with gas masks and protective clothing, which probably would become less effective as the gas concentration became increased with time.

It was Roosevelt who vetoed the use of gas on Iwo Jima out of concern for world public opinion.

I think this was meant for Deaf Smith as I haven't made any comments about gas.

Wizard
08-18-2010, 02:33 PM
Wizard, I apologise for having given inaccurate altitudes of detonation for both A-bombs.

No apology necessary. The point is pretty much irrelevant to the present discussion; I mentioned it only in the interest of historical accuracy.


I did read Leslie Grove's very informative tome some years ago, and yes, I'm reasonably familiar with the detonation mechanisms in each case.

Then you will understand that the atomic bombs of 1945 were considerably more delicate and sensitive to disruption of their internal mechanisms than any bomb dependent on chemical explosives alone.


My point with regard to the Grand Slam casing is that it was designed to survive impact without distorting (It was, in effect, battleship armour,).

Both of the atomic bombs used on Japan in 1945, though intended as air burst weapons, were encased in heavy armor. I'm not sure what was the reason for this, since, if they worked as intended, they would experience no impact.


The way I thought about it was: put a nuclear payload in a non-distorting casing, and one then has a very useful though admittedly dangerous weapon, capable of either digging out the defenders, or rendering them neutralised in place.

That the Grand Slam was successfully employed with a conventional payload suggested to me that it might be successful with a nuclear payload.

While I understand your point, I do not completely agree that the technology of atomic bombs was sufficiently understood in 1945 to allow them to be used successfully as tactical nuclear weapons against fortifications and underground defenses.


In short, the "dig-down" at impact for which Grand Slam was designed would be considerably augmented by the nuclear payload. That detonating such a payload underground in such a manner would be less efficient in causing casualty rates I do not debate: the point is plain enough.
However: the purpose of a nuclear payload Grand Slam would not be `a-priori to cause casualties directly.
The purpose would be to cause cave-in, implosion of the caverns/hollow spaces/caves nearby, and thus render the occupants unable to successfully defend against an incoming attack.
Accordingly, my thought was that the "loss of efficiency" in terms of over-all casualties as a result of detonation would have been accepted, as part of the price of what would amount (imho) to super-efficiency in the undermining/cave-in/implosion of cavern-spaces role.

Kind and Respectful regards Wizard my friend, Uyraell.

First of all, I do not believe that the grand slam bomb casing could be hardened sufficiently to protect the internal mechanism of a nuclear weapon while still allowing the bomb to impact the ground with sufficient force to dig it in deeply enough to be effective against fortified underground defenses. However, this is an argument which hinges on technical data that, in all probability, is classified, and to which neither of us have access. So I freely admit I cannot prove my case. However, it seems to me that the US had not tested any such bombs by 1945, and would not be likely to waste such a valuable weapon in a manner that left anything to chance.

Secondly, I think the power of an underground nuclear blast would not be sufficient to produce catastrophic destruction over a widespread area. Again, in 1945, there had been no testing of underground nuclear explosions, and such things as optimum depth, yield, and destructive power were completely unknown. It wasn't until the US began testing nuclear devices that could be potentially used for excavating canals, artificial harbors, etc. in 1962, that such data became available. Therefore the use of atomic bombs to destroy underground fortifications would be largely experimental in 1945. Wikipedia suggests that underground nuclear explosions generate "minor earthquakes" http://en.wikipedia.org/wiki/Effects_of_nuclear_explosions which might trigger disruption of nearby fault lines and cause a major quake. But this is a pretty tenuous theory, and I doubt any military staff would be willing to base invasion plans on such a possibility.

Given, that an atomic air burst would kill or incapacitate only those defenders caught above ground, and there is a distinct possibility that an underground atomic detonation might not occur at all, or might destroy only those fortifications within a few hundred yards proximity, I believe there is a definite possibility that the atomic bombs, had they been used in a tactical role, might have been very disappointing weapons.

I don't know if this was understood, or even considered, by the senior American military leadership. The various nuclear tests carried out between 1945 and the mid-1960's certainly suggests to me that there was a great deal that needed to be learned about the potential uses of atomic weapons before they could be successfully employed as suggested in the plans for Operation Downfall.

pdf27
08-18-2010, 03:17 PM
Important technical point here - a ground burst is, in nuclear terms, one where the fireball touches the ground, not the device itself. For a 20kT device, that means an initiation at ~750ft above ground level or less - something they would be keen to avoid due to issues with the reliability required of the fusing system, but hardly insuperable.

Furthermore, against the sort of fortifications that the Japanese would have constructed, an airburst would probably be better. If I'm using my Nuclear Bomb Effects Computer correctly (goes with my copy of [i]The Effects of Nuclear Weapons[i], which is highly recommended btw) then for a 20kT optimum airburst the max overpressure is 6.5 PSI @ 1 mile - which drops to 3.25 PSI for a surface burst. The surface burst provides an overpressure of 6.5 PSI at 0.65 miles - so a surface burst will only have 40% of the effectiveness of an airburst.

Uyraell
08-19-2010, 03:24 AM
Given, that an atomic air burst would kill or incapacitate only those defenders caught above ground, and there is a distinct possibility that an underground atomic detonation might not occur at all, or might destroy only those fortifications within a few hundred yards proximity, I believe there is a definite possibility that the atomic bombs, had they been used in a tactical role, might have been very disappointing weapons.



The Grand Slam had been originally designed by Barnes Wallis for release at between 22,000 and 23,000 feet altitude, from which height it would accelerate to transonic speed in free-fall, to impact the ground to a depth of variously 40, 60, or 90 feet, depending on the density of the ground at the target. (ie: softer ground, greater penetration to detonation depth.) Source: R.V. Jones: "The Secret War".

At Beilefeld, the weapon had been dropped from just on 14,000 feet, and apparently penetrated to a depth of some 24 to 28 feet, as confirmed by post-war research. I agree that after that information, little else is available. I agree any related information is likely to be still classified.

Now, to confound matters a little: I agree that tactical employment of a nuclear bomb in the manner I suggest in 1945 may well have proven to be a disappointment on the field of battle.
That in no way alters my view that it could well have been feasible, however. A nuclear payload in a Grand Slam casing does not, to me, seem that far-fetched.

You've made very many extremely good points, Wizard my friend, and I've thoroughly enjoyed our exchanges in this discussion.
While I agree with much of what you've said, Wizard, my original thought in my initial post was that what I suggested could easily have been achieved. Would it have resulted in a successful tactical employment? Possibly: I don't put the odds of success at greater than 45 to 50 % at best.

Kind and Respectful regards Wizard my friend, Uyraell.

Nickdfresh
08-19-2010, 07:22 AM
Isn't it possible that a nuclear detonation over subterranean fortifications may well have sucked the oxygen out of the air?

Rising Sun*
08-19-2010, 08:16 AM
Isn't it possible that a nuclear detonation over subterranean fortifications may well have sucked the oxygen out of the air?

pdf 27 will know, but I suspect not because I think the heat is generated by the atomic reaction rather than combustion which consumes oxygen.

People died from asphyxiation in the Tokyo firestorms from convential bombs but I don't think this was an issue at Hiroshima and Nagasaki.

Perhaps air might have been sucked out of caves by the reaction after the explosion displaced air above ground, but I don't know whether this would have killed or injured the inhabitants.

pdf27
08-19-2010, 02:27 PM
pdf 27 will know, but I suspect not because I think the heat is generated by the atomic reaction rather than combustion which consumes oxygen.

People died from asphyxiation in the Tokyo firestorms from convential bombs but I don't think this was an issue at Hiroshima and Nagasaki.

Perhaps air might have been sucked out of caves by the reaction after the explosion displaced air above ground, but I don't know whether this would have killed or injured the inhabitants.

Umm.... the nuclear initiation itself doesn't suck much (any) oxygen out of the air. However, remember that a nuclear device is the mother of all firebombs, and highly likely to start a firestorm on a suitable target (although strangely a lot depends on bomb size).

I can't be bothered to dig my piecutter out right now, but the short answer is "maybe". A suitably sized airburst over say Hamburg, Dresden or Tokyo would probably have caused a similar firestorm.

Wizard
08-19-2010, 07:09 PM
Umm.... the nuclear initiation itself doesn't suck much (any) oxygen out of the air. However, remember that a nuclear device is the mother of all firebombs, and highly likely to start a firestorm on a suitable target (although strangely a lot depends on bomb size).

I can't be bothered to dig my piecutter out right now, but the short answer is "maybe". A suitably sized airburst over say Hamburg, Dresden or Tokyo would probably have caused a similar firestorm.

Though I am by no means a technical expert on these matters, I do know that a firestorm is only possible if a certain temperature level is maintained for a certain period of time. That depends on the temperature level reached by the initiating explosion or incendiary device, and the amount of combustible material it has available to feed on.

I may be wrong, but it's my understanding that neither the Hiroshima nor the Nagasaki atomic explosions triggered firestorms. The heat they generated, while certainly intense enough, lasted for too short a period of time to create the requisite conditions.

pdf27
08-20-2010, 12:45 AM
You aren't relying on the device creating sufficient heat - frankly it won't. It will however create sufficient heat to set fire to a very large area, which when combined with the right atmospheric conditions will create a firestorm. Certainly from photos of Hiroshima and Nagasaki it would appear that everything capable of burning close to Ground Zero has done so - note the way that a number of masonry buildings appear pretty much intact, so the flattening of the area was not done by blast. Whether that technically qualifies as a firestorm or not I don't know, but the effects can't have been all that dissimilar.

http://newsjunkiepost.com/wp-content/uploads/2009/08/hiroshima_wideweb__430x323.jpg

Wizard
08-20-2010, 01:33 AM
You aren't relying on the device creating sufficient heat - frankly it won't. It will however create sufficient heat to set fire to a very large area, which when combined with the right atmospheric conditions will create a firestorm. Certainly from photos of Hiroshima and Nagasaki it would appear that everything capable of burning close to Ground Zero has done so - note the way that a number of masonry buildings appear pretty much intact, so the flattening of the area was not done by blast. Whether that technically qualifies as a firestorm or not I don't know, but the effects can't have been all that dissimilar.

http://newsjunkiepost.com/wp-content/uploads/2009/08/hiroshima_wideweb__430x323.jpg

There's no question that almost all the combustible structures near the hypocenter of both the Hiroshima and Nagasaki atomic bomb attacks were completely destroyed by blast and heat. There is also no question but that an atomic explosion can create a firestorm under certain conditions, but neither of the two atomic bombs dropped on Japan were sufficient to create a firestorm.

The definition of a firestorm is; "A large usually stationary fire characterized by very high temperatures in which the central column of rising heated air induces strong inward winds which supply oxygen to the fire"

The crucial element of a firestorm are the very strong (some definitions state 'hurricane force") winds which develop and feed oxygen and more combustible material into the central fire.

The bombing of Dresden created a true firestorm, as did the 9-10 March, 1945, incendiary bombing of Tokyo. Witnesses in both cases described very strong winds created by the fires which sucked small vehicles, trees, roofs, and other items into the fire, along with people and animals. These are the only two instances of which I am aware, of true firestorms, although it's entirely possible that the incendiary bombing campaign carried out by the US XXI Air Force against Japanese cities in 1945, may have created others.

pdf27
08-20-2010, 02:32 AM
Read the original comment in post #17 ;)

Wizard
08-20-2010, 11:59 AM
Read the original comment in post #17 ;)

Have already read the comment, but read it again at your suggestion.

I assume you stand by your original statement that a nuclear explosion "doesn't suck much (any) oxygen out of the air"?

Since neither of the nuclear explosions over Japan in 1945 appear to have started a firestorm, it seems to me the prospect of a nuclear explosion killing or incapacitating defenders in underground defenses through oxygen depletion would have to be very slight.

Question; has any atmospheric nuclear explosion anywhere in the world, under any circumstances, been known to have created a firestorm?

pdf27
08-20-2010, 02:10 PM
Correct. A nuclear initiation essentially consists of a very small ball of incredibly hot gas. The soft X-rays given off by this ball superheat a larger volume of air (the fireball), with the thermal pulse and blast effects coming from this fireball. There will be a small amount of Oxygen within the fireball reacting with Nitrogen in the atmosphere (one of the original concerns in the Manhattan project was that the atmosphere would catch fire as a result), but that's about the only actual oxygen consumed by the device itself. Hence the "much (any)" comment - some will be consumed, but it's an insignificant amount. The blast and thermal pulse however will replicate much of the destruction caused by the RAF fire raids of WW2.

I'm pretty sure there won't have been any firestorms as a result of nuclear initiations anywhere in the world - Hiroshima and Nagasaki are the only candidates as the atmospheric nuclear tests which have taken place were all AFAIK situated to minimise what could catch fire in order to reduce fallout.

Wizard
08-20-2010, 08:41 PM
...I'm pretty sure there won't have been any firestorms as a result of nuclear initiations anywhere in the world - Hiroshima and Nagasaki are the only candidates as the atmospheric nuclear tests which have taken place were all AFAIK situated to minimise what could catch fire in order to reduce fallout.

Well, I suspect then that the answer is no, no atomic explosions have ever initiated true firestorms.

I have seen references to a "firestorm" occurring at Hiroshima, but I believe this is a loose application of the term; the description is too brief and only mentions a "whirlwind" associated with the blaze triggered by the blast. There is no mention of the very strong winds accompanying a true firestorm, nor of oxygen or other combustible materials being sucked into the fire. It appears that both Hiroshima and Nagasaki experienced fires of severe intensity, but of too brief a duration to generate the conditions for a true firestorm.

I have reviewed all of the accounts in my possession of the Nagasaki atom bomb explosion, and none of them seem to mention anything other than a large conflagration triggered by the blast. No mention of very strong winds or materials being sucked into the fire is made.

Deaf Smith
08-20-2010, 10:27 PM
Do you have a source that indicates gas would be introduced into the underground fortifications by use of artillery shells? Or are you just surmising that would be the method? It doesn't seem to be a very effective way of using poison gas. On Iwo Jima, I believe, the plan was to lay down a gas barrage on the surface of the island, and then land specially trained troops who would pump gas into the fortifications through the ventilation openings. The Japanese would counter, of course, with gas masks and protective clothing, which probably would become less effective as the gas concentration became increased with time.

Wizard,

In WW1 shells were THE main way gas was used. Yes it was also released by canister so prevailing winds would carry it over the enemy lines but that depends on the winds.

If you have watched the PBS documentary, The American Experience Victory in the Pacific

http://www.pbs.org/wgbh/americanexperience/films/pacific/

In fact you can watch the video!

http://video.pbs.org/video/1449123274/

It mentioned using gas in the assault as well as Gen. Marshal's idea of nuking the beaches.

Deaf

Wizard
08-20-2010, 11:25 PM
Wizard,

In WW1 shells were THE main way gas was used. Yes it was also released by canister so prevailing winds would carry it over the enemy lines but that depends on the winds.

Yes, I'm aware that artillery barrages were the primary method of releasing gas on enemy lines during WW I. However, the enemy generally wasn't dug into caves and underground bunkers during WW I, and it just seemed to me that firing a gas shell into a cave entrance wouldn't be a very efficient way of delivering the large quantities of gas that would be required to saturate the many tunnels and deep chambers typically found in Japanese defensive fortifications.

Wind and other meteorological conditions are always of concern when using poison gas, no matter what the delivery method. During WW I there were several occasions when changing winds blew the poison gas back in the faces of those who had released. Rain, winds, temperature, humidity, even clouds and sun can all have unpredictable effects when using poison gas.

On Iwo Jima and Okinawa, the Americans sometimes pumped gasoline into the ventilation shafts of recalcitrant enemy fortifications and then ignited it with WP grenades. This seems like a much better way of delivering poison gas, as well, especially if the fortifications are very extensive.

In any case, I was just curious if there were any concrete pl;ans or if any American troops had been trained in any tactics applicable to the delivery of poison gas, in anticipation of the Kyushu landings.


If you have watched the PBS documentary, The American Experience Victory in the Pacific

http://www.pbs.org/wgbh/americanexperience/films/pacific/

In fact you can watch the video!

http://video.pbs.org/video/1449123274/

It mentioned using gas in the assault as well as Gen. Marshal's idea of nuking the beaches.

Deaf

Thanks for the links, I had not seen these documentaries.

pdf27
08-21-2010, 03:57 AM
Well, I suspect then that the answer is no, no atomic explosions have ever initiated true firestorms.

I have seen references to a "firestorm" occurring at Hiroshima, but I believe this is a loose application of the term; the description is too brief and only mentions a "whirlwind" associated with the blaze triggered by the blast. There is no mention of the very strong winds accompanying a true firestorm, nor of oxygen or other combustible materials being sucked into the fire. It appears that both Hiroshima and Nagasaki experienced fires of severe intensity, but of too brief a duration to generate the conditions for a true firestorm.
Agreed. However, I would suggest that the duration of the fire is a function of the nature of the target rather than the nature of the bomb - the incendiaries dropped on Dresden or Tokyo typically had a pretty short duration burn too. However, there is one possibility that is bomb-related - and that is the amount of blast damage created. When trying to create a firestorm, the RAF would typically drop large HE bombs first to break open roofs, etc. to let the incendiaries in, whereas completely flattening an area will create a firebreak. It is possible that the way a nuclear device works (thermal pulse first, then blast) may have a similar effect in damping down a fire. So much depends on device size and distance from the initiation point however - blast and thermal effects do not drop off in the same way with distance.

Wizard
08-21-2010, 12:53 PM
Agreed. However, I would suggest that the duration of the fire is a function of the nature of the target rather than the nature of the bomb - the incendiaries dropped on Dresden or Tokyo typically had a pretty short duration burn too. However, there is one possibility that is bomb-related - and that is the amount of blast damage created. When trying to create a firestorm, the RAF would typically drop large HE bombs first to break open roofs, etc. to let the incendiaries in, whereas completely flattening an area will create a firebreak. It is possible that the way a nuclear device works (thermal pulse first, then blast) may have a similar effect in damping down a fire. So much depends on device size and distance from the initiation point however - blast and thermal effects do not drop off in the same way with distance.

I concur, and yes, the duration of the fire would normally more to do with the nature of the target than the type of bomb employed. I did not suggest otherwise. On that topic, it's informative to note that during the Tokyo incendiary bombing of 9-10 August, the bomber stream was not one big formation, but rather a long line of bombers that, in effect, kept adding incendiary bombs to the fire over a period of several hours. The planners of the Tokyo bombing did add some high explosive GP bombs to the bomb loads, in order, I presume, to break up and scatter combustible material and possibly, to deter fire fighting personnel.

pdf27
08-21-2010, 06:39 PM
I'd be curious as to whether that was down to logistical concerns (e.g. airfield restrictions) or deliberate design. The RAF usually tried to get very concentrated raids over the target, although that may have been more to do with overwhelming the German nightfighter defence - not a problem the USAAF faced over Japan!

Nickdfresh
08-21-2010, 07:09 PM
U.S.A.A.F. B-29 bombers were flying much lower and stripped of much of their armament than their European counterparts as the Jet Stream made high altitude bombing far more difficult IIRC. Perhaps the need for concentration over the target was mitigated by the increased accuracy and low levels?

Wizard
08-21-2010, 09:28 PM
I'd be curious as to whether that was down to logistical concerns (e.g. airfield restrictions) or deliberate design. The RAF usually tried to get very concentrated raids over the target, although that may have been more to do with overwhelming the German nightfighter defence - not a problem the USAAF faced over Japan!


U.S.A.A.F. B-29 bombers were flying much lower and stripped of much of their armament than their European counterparts as the Jet Stream made high altitude bombing far more difficult IIRC. Perhaps the need for concentration over the target was mitigated by the increased accuracy and low levels?

The reason the 9-10 August Tokyo incendiary raid did not feature compact formations of B-29's had to do with many factors.

As PDF27 points out there were no significant numbers of night fighters over Tokyo and the few that were there, were ineffective, therefore there was no need for tight formations to concentrate defensive firepower. In fact, General LeMay ordered the B-29's that participated stripped of most defensive armament so they could carry more bombs.

Normally, when conducting high altitude bombing missions using high explosive bombs, the B-29's used very compact formations to concentrate the bomb patterns and increase the number of bombs on, or near, the target. In order to achieve these compact formations with large numbers of aircraft, the first bombers to take off would circle at a rendezvous point while the later bombers joined up, and the formation was completed. This required an extra margin of fuel which meant the B-29's had to carry smaller bomb loads. For the Incendiary raids, LeMay deleted the extra fuel margin in favor of heavier loads of incendiaries, thus the bombers simply took off and headed for the target without formating. Tight bomb patterns were not required due to the very low bombing altitudes (7,000 to 14,000 feet) of the incendiary raids. The main bomber stream was proceeded by "pathfinder" planes which dumped their flares and incendiary bomb loads in an "X" pattern. Succeeding bombers simply bombed into the heart of the growing fires.

North Field on Tinian, from whence most of the B-29 raids originated, was, in August, 1945, the largest air field in the world with four identical runways which could accommodate large numbers of aircraft taking off, but it still could not launch enough aircraft to obviate the need for the aircraft to rendezvous, if tight formations were required.

doramide7
09-24-2010, 09:36 PM
I can't agree with this.

Both atomic bombs which were actually used on Japan were quite complex in their arrangement, and the detonating fuse for the chemical explosive was probably the simplest part of their mechanism. The bomb used at Hiroshima relied on bringing together two small (a few pounds each) masses of fissile material to form a critical mass. The "gun type" bomb did this by using essentially a gun barrel to fire one mass into the center of another mass thus achieving a mass of critical proportions.

Wizard
Well guys, I'm sure the RAF could have got 1000 Lancasters to pattern bomb the invasion beaches with Grand Slams. Now THAT would have taken care of the caves!

In fact, I wish at Iwo Jima they had done just that using B-29s to carry the Grand Slams and maybe have stopped alot of them from using the caves.

Happly, the Japanese surrendered and we didn't have to try moving soldiers over radioactive ground or firing mustard gas shells into caves (for you see that is how they would have delivered the gas, with shells.)

Wizard
09-24-2010, 10:14 PM
Well guys, I'm sure the RAF could have got 1000 Lancasters to pattern bomb the invasion beaches with Grand Slams. Now THAT would have taken care of the caves!......

You're sure? Based on what, exactly?

Did the RAF have that many Grand Slam bombs in stock? What base would the Lancasters have flown from? Could they have been sure of even hitting the underground fortifications? And even if they did, just how effective would such bombs have been against underground fortifications? And just what effect would giant craters all over the invasion beaches have had on the Allied troops, tanks, and other vehicles which would have had to traverse them?

No offense, but I'd like to hear from some experts who actually knew the what kind of performance to expect from the Grand Slam bombs, and the other factors I've questioned, so could you please cite some authoritative sources?

pdf27
09-25-2010, 02:10 AM
He's been banned as a spammer anyway, but for your actual point...

The effects of a bomb (overpressure, blast, etc.) decline with the cube of the distance from the bomb to the target. Double the distance, you have an eighth of the effect. Hence, doubling the size of the bomb only gives a 25% increase in useful area - which is why big bombs are only used against either extremely hard targets (railway viaducts, the V-3 site, etc.) or where damage needs to be kept very concentrated (the blockbusters dropped during the RAF fire raids - removing the roofs in a large, continuous area was more effective at getting a big enough fire started than smaller, spaced-out bombs).

The other point people miss about the Tallboy and Grand Slam bombs is that they needed to be dropped from a long way up to be effective - they were in fact originally designed to be dropped from 40,000 ft, to explode below their target and undermine it. Barnes Wallis was planning a newly designed bomber just for these bombs, but it never got off the drawing board for obvious reasons. The B-29 could probably just about have done this with Tallboy, but it wasn't until the B-36 came along that this was possible with Grand Slam - by which time tactical nuclear weapons had made the entire idea obsolete anyway. Stripped out Lancasters could make it up to about 20,000ft with Tallboy and a bit less with Grand Slam, which was just about enough to work but not enough to use the bombs as originally designed.

It's also worth noting that only a few of the very best squadrons in the RAF ever dropped these bombs, starting with 617 squadron whose motto "Après moi le déluge" may give you a hint as to where you might have heard of them before. The bombs were very rare, took an enormous amount of time to make and each aircraft only got one to drop at a time - so were only ever used for very, very precise targets and highly trained crews.

Wizard
09-25-2010, 12:58 PM
He's been banned as a spammer anyway, but for your actual point...

The effects of a bomb (overpressure, blast, etc.) decline with the cube of the distance from the bomb to the target. Double the distance, you have an eighth of the effect. Hence, doubling the size of the bomb only gives a 25% increase in useful area - which is why big bombs are only used against either extremely hard targets (railway viaducts, the V-3 site, etc.) or where damage needs to be kept very concentrated (the blockbusters dropped during the RAF fire raids - removing the roofs in a large, continuous area was more effective at getting a big enough fire started than smaller, spaced-out bombs).

The other point people miss about the Tallboy and Grand Slam bombs is that they needed to be dropped from a long way up to be effective - they were in fact originally designed to be dropped from 40,000 ft, to explode below their target and undermine it. Barnes Wallis was planning a newly designed bomber just for these bombs, but it never got off the drawing board for obvious reasons. The B-29 could probably just about have done this with Tallboy, but it wasn't until the B-36 came along that this was possible with Grand Slam - by which time tactical nuclear weapons had made the entire idea obsolete anyway. Stripped out Lancasters could make it up to about 20,000ft with Tallboy and a bit less with Grand Slam, which was just about enough to work but not enough to use the bombs as originally designed.

It's also worth noting that only a few of the very best squadrons in the RAF ever dropped these bombs, starting with 617 squadron whose motto "Après moi le déluge" may give you a hint as to where you might have heard of them before. The bombs were very rare, took an enormous amount of time to make and each aircraft only got one to drop at a time - so were only ever used for very, very precise targets and highly trained crews.

All points I was aware of, hence my questions. And the poster had not been banned at the time I posted my response. I suspect the poster wasn't serious about the issues anyway, since his message seemed to ignore the obvious negative factors of such a suggestion. The book I have on Barnes Wallis details the problems associated with the design, production, and use of very large bombs, and gives a good idea of the limitations of these very specialized weapons.