I’m still doubtful that any sort of successful test took place. However, even if they only actually tried (..and failed.) to detonate some sort of prototype it’s very interesting, as would be the physical size if this took place, in relation to delivery methods.
For sure there is a lot of hogwash talked about what was found in Germany at the end of the war. Yet, there is no denying that Germany was, factually, well ahead in many areas. Their jet engines were axial-flow, they had swept-wing jet fighters in service, they had the V1 & V2, – some of their weaponry, such as tanks were vastly superior to the average allied stuff – the list is endless and can’t be simply dismissed. Fortunately, they were led by a small cadre of fanatical idiots.
A fact often overlooked is that the Germans had the worlds ONLY Supersonic wind-tunnels. These fell into the British sector at the end of the war and I was told by a British test-pilot that they were spirited back to the UK and were very influential. I think there were at least two. A subject well-worth a thread of it’s own I would say….! ( I wonder if any have survived…? – but I digress.)
Politics is not relevant here, nor is it really a place to posture and moralise. (The Allies scooped-up a lot more than just the scientists – conveniently forgotten now – , but also those who knew where the wealth etc was hidden.) Not because they aren’t important, but because we’re here to talk ‘Historic Aviation’.

Regarding the Germans not having a means to deliver a bomb;- The V2 would have been ideal. If that didn’t have the payload, they had plenty of a/c that were large enough.
Getting back to what was actually found by the Allies at the end of the war;- I do recall seeing some photos of a reactor at Haigerloch, but I don’t recall ever seeing any images of a weapon ‘dirty’ or otherwise.
I should have looked earlier, but there is a topic on the dreaded Wikipedia;-

http://en.wikipedia.org/wiki/German_atomic_bomb_project

Much of this is over my head, but there is an interesting footnote;-

Recent developments[edit]

A book by Rainer Karlsch, Hitlers Bombe, published in 2005, alleged that Diebner’s team conducted the first successful nuclear weapon test of some type (employing hollow charges for ignition) of nuclear-related device in Ohrdruf, Thuringia on 4 March 1945.[107] However, Karlsch has been criticized for displaying “a catastrophic lack of understanding of physics” by physicist Michael Schaaf, who is himself the author of an earlier 2001 book about Nazi atomic research which controversially paints Heisenberg as a pacifist who allegedly tried to prevent development of a Nazi nuclear weapon, while Karlsch himself has acknowledged that he lacked absolute proof for the claims made in his book.[108]
Shaaf’s own motives for denouncing Karlsch might be explained by the underlying theory expounded in Michael Schaaf’s book that Heisenberg did not support development of a nuclear weapon which was discredited in Karlsch’s 2005 work which uncovered Heisenberg’s speech notes from the Harnack Haus conference of July 1942, located in KGB archives at Moscow. These speech notes revealed Heisenberg was a strong advocate for development of a Nazi nuclear weapon.[109] Retired Luftwaffe Field Marshall Erhard Milch also recounted and corroborated the speech notes found in KGB archives.
A similar project was described in David Irving’s 1967 book The Virus House, where it was claimed that some of Diebner’s researchers had unsuccessfully attempted to produce fusion using conventional explosives and heavy paraffin as a deuterium carrier. Irving also describes a further experiment in 1943 carried out by Trinks and Sachsse, which used a hollow sphere of silver filled with deuterium, imploded by conventional explosives. Again it was unsuccessful, no trace of radioactivity being produced.[110]
Science historian Mark Walker also published his analysis in 2005,[111] and in 2005 Karlsch and Walker published an article on the controversial historical evidence, briefly referenced in the article.[112] The Physikalisch-Technische Bundesanstalt (PTB, Federal Physical and Technical Institute) tested soil samples in the area of the alleged test, and in 2006 it issued its results: keinen Befund (nothing found).[113] Karlsch published a follow-on book with Heinko Petermann to elaborate on issues raised in his first book.[114]

On the face of it then, if the Ohrdruf device was a serious attempt to detonate a device, it probably failed. Probably. As a complete layman in these matters, I just can’t imagine such a detonation passing unnoticed.
Reading through all the bumpf, I suppose the main thing that hits me is that they were certainly right at the cusp of getting their fusion reactor to work. Had that been the case, the path to a fission device would have been that much more direct and certain. Had Japan not attacked the US, – or done so much later, the cards might all have played-out differently. I also recall that Van Braun drew-up plans for larger, multi-stage developments of the V2, capable of reaching the USA. All of this also has a good deal of bearing on the silly criticism often levelled against RAF Bomber Command.
How much of what the Germans were doing was known to the Allies can only be speculation, but they seemed to have had a pretty good idea. No wonder they chose to concentrate on Winning the war in the ETO first.

That interests me is that the general opinion, for years, seems to have been that in fact, the Germans were miles behind the Allied effort. I’m curious about the ‘when, where and what’ of these tests. I’ve always had the feeling that had the war dragged on for another year or so, we might have had some nasty surprises. That said, I read the other day that the US high command planned to drop the A-Bomb on Germany too, but the rapid German collapse at the end of 44/early ’45 obviated that, thank God.
The ‘what if’s’ don’t really concern me, but I think that if these tests did in fact take place, it puts a very interesting spin on that final phase of the war. There was a huge ‘gold-rush’ for German science and personnel. There may even still be some stuff that’s still Classified. One is forced to wonder which side got hold of all the research etc…..