...I find some of your arguments, below, dubious.
Well you don't have to because I can back up what I said.
Blast Waves/Pressures:
An air blast does not transfer a strong concussive effect on the ground as air is far less dense then earth about 1.2kg/m3 and 1500kg/m3 respectfully, thus only about 1/1000th of the energy from the air shockwave is transferred to the ground (for a given radius) Concrete is about 2500kg/m3 So even a lightly buried bunker is only going to have about 0.048% of the energy from the blast be transferred to it. Negligible.
A ground burst by comparison for a given radius is about 60%.
This is why the 'Grand Slam' bomb was developed to penetrate into the ground/concrete of a bunker and
then detonate as a literal ground burst transferring the whole 6.5tons of TNT of blast directly at the structure.
About 1 in 20 people survived at the very centre of the Hiroshima and Nagasaki blasts with little more than having been in their basements, hardened structures or underground at the time with no real formal 'bunkered' protection. Fact. You can go look that up from any site/book/source whatever that has statistics on the civilians killed.
Akiko Takakura survived the detonation of the 16kt warhead at a distance of just 300 meters from the hypocenter, with only minor injuries, due in most part to her position of residing in the lobby of the bank of Japan, a reinforced concrete building, at the time of the Nuclear explosion. To name a specific case.
A typical German blast door would be rated to a couple hundred kg, but since they vary and have differing statistics, then one would have to ask the number of blast doors and size of the blast void behind them, it would be very difficult to crunch the numbers unless considering specific examples.
To give an idea of even how good basic German bunker design such as was used on the Atlantic wall in the channel islands, one bunker took about 70 1-ton shells off a British ship on Alderney and the door is still intact today (not claiming these shells were direct hits, but the bunker was able to withstand heavy continued bombardment without being compromised).
Blast Size & Effect:
For those that assume that a major battle would be a good location you have to consider the blast and damage radius; from the bombs dropped on Japan we know that only about 26% of people were killed within 3mi of the epicenter of the blast, and that ~85% of all those killed were within an area about half a mile in radius.
Hence you've got about a 2km blast zone where it will be tactically useful.
OTOH I don't wonder about this; this is plainly wrong.
Sure operations ranged over many kilometers of frontage. That's not to say that there weren't areas more important than others. And more importantly, if the conventional friendly troops have appropriate plans, the wonder weapon will be a battle winner. In that it will open a sudden, unexpected breach in the enemy line, which armored friendly troops can immediately exploit.
Really this is wrong is it?
Sources;
http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki
http://www.nukefix.org/weapon.html
Numbers don't generally lie.
For most battles you can find a battle map showing the scale of the battle. If we take the Battle of the Bulge for instance;
and we know that the nuclear blasts at maximum are about 3mi in radius, then one can get a comprehension of the scale of the battle. Remember only about 1mi represents the blast centre of tactical effectiveness.
We also have to remember that Allied and Axis forces would be typically very close together, meaning that to drop a bomb on the enemies front means your also dropping it on your own men. Furthermore the Germans aren't going to be stupid if they see Allied troops falling back they are going to pursue, or realise that they they are retreating so that the German positions can be bombarded. Thus the Germans know they have to move out from where they are.
Another battle map with scale;
http://upload.wikimedia.org/wikipedia/commons/1/1c/Aachen.jpg
If a bomb had been dropped at Aachen the entire forest would have been burnt to a crisp, Allied and Axis troops alike ¬.¬
Finally remember the Mining of the German trenches at the Somme in the Great War? The Allied Generals know they can't go right in after dropping the bombs because their troops will get covered by radioactive particulate, and the generals knew this long before the bombs were dropped in Japan. They also knew that the radiation would decay exponentially over time, thus it is immediately very strong enough to kill of people within hours or days, but after about 48hrs it has decayed a thousand times to a low level which might be considered safe to move into the region.
Hence they cannot move into a sudden hole in the line, since they know they have to wait about 2 days before they can move into the area, or condemn the troops they sent to a very painful and messy death from radiation sickness (and they did know about this before the atomic bombing of Japan, but what they didn't know with much certainty was the scale of effect radiation would have on troops).
The generals knew that a few tens of people had been killed from radiation sickness throughout the Manhattan Project and before and were well knowledgeable in it effects, but also weren't certain of the level of contamination from a blast. Hence 48hrs was stated as a minimum time to wait before moving into a blast zone (REF: Colonel Seeman advising Major General Hull on Operation Downfall).
While yes,
today we know that it would be possible to a level to move earlier than 48hrs with adequate forms of protection and preparedness.
Then they didn't know quite how strong the radiation was in the environment, what black rain was or how to deal with the level of devastation wrought.
Choice of Target(s):
Look up the Interim Committee [
http://en.wikipedia.org/wiki/Interim_Committee] as well as what Allied Intelligence knew on the Nazi atomic bomb project. It was well known to the Allies in 1943 that the Germans would not (likely) be able to catch up with the Allied effort, hence Szilards and Einstein’s fear that the Nazis may build the bomb were actually unfounded.
The scientists at the Manhattan Project were not informed of this fact and so right up until before the fall of Germany were under the impression that the Nazis were still working on the weapon and so they were building theirs.
The point being that the Allies knew that they didn't have to build the bomb anyway, but it was built anyway. Thus when it appeared that the bomb might be ready before the fall of Germany the awkward question had to be asked of how should it be used.
There is much debate on the issue and many sources and opinions here is an overview article; [
http://www.anzasa.arts.usyd.edu.au/ahas/bomb_historiography.html]
The fact of the matter is that it was decided not to bomb Germany, and that Japan should be bombed instead. Plus there is the fact that this thread is about a tactical use, not a strategic use. It is likely that had the bomb been used in a strategy context in Germany it might have been the Ruhr or another similar strategic target, but it is unlikely to have been a city although claim and counter claim are pointless without reading the various sources, for that reason we cannot hope that people here will do so, and so arguing city or not city is pointless. From what I know/read/seen I believe that the Allies would not have made themselves another Dresdan.
The Allies were always very conscious about Nazi propaganda because occupied Europe
did believe it (read up on its effectiveness), and they also had a moral imperative to be 'better than the Soviets' war crimes were something that it was important the Allies be not seen to conduct after they had called the Soviets out on it.
As a final aside, when, in all human history, during a war, was a new revolutionary weapon used for demonstration purposes only, just in order to impress the enemy?
Thermopylae springs to mind right away...
Then you have siege artillery from the Dark Ages and Medieval era desired to make castles surrender without a fight since you could reduce their walls.
Then there is the development of the Musket/Arquebus whose use against various medieval lords and later new world/oriental 'primitives' was more than a demonstration enough.
Then there is the machine-gun...
The list isn't endless, but half of just even having a military, is just a demonstration of will and capacity for a nation to fight if called for. Look at Switzerland for example
.
EDIT: With that last section, I know that's not exactly what you meant, but my implication from the examples is that a demostration does generally involve some blood. At the same time, the point of 'shock and awe' is to spill as little blood as possible in creating that 'shock and awe', the Japanese were a very 'fanatical' people therefore it is likely they would have needed more convincing than the Germans the game was up, particularly since their armies were well on the retreat by mid '44, while Japan still held Manchuria, parts of China and much of their home islands still and had the deathwish spirit to boot.