By Colin Salt
One of the biggest cliches in alternate history is a German atomic bomb in World War II. This fits better with the other cliche of Operation Sea Lion succeeding than one might imagine, because both had an extremely remote (to put it mildly) chance of success. In spite of conspiracy theories, recent atomic forensics has reinforced the conventional wisdom that the German program was moribund.
Take the Little Boy-style gun-type bomb, which is the simplest and easiest way to build a nuclear weapon. In a short and oversimplified explanation, it amounts to just firing one chunk of highly enriched uranium into another at high speed. James Kunetka's Parting Shot had this as the secret nuclear weapon the Germans made, and rightfully so. But even that has challenges of its own. Amazingly, a well-documented "control group" exists: The atomic program of apartheid South Africa, which succeeded in making several functional warheads before being dismantled completely. This has been considered one of the best-run nuclear weapons of any country, and one of the choices it made was going for a gun-type. In contrast, the German program was anything but well-run (to the point where I'd argue that it ranked among the worst-handled nuclear weapons attempts in history, with the only competition coming from the hopeless attempt by Gaddafi's Libya.)
It still took the South African's multiple years to get the basic design right, and this was in peacetime with a considerable amount of hindsight that the Germans obviously would not have. Furthermore, the construction of the devices was delayed significantly by the biggest bottleneck for a gun-type nuclear bomb: The need for large amounts of highly enriched uranium. South Africa's HEU enrichment program snarled and stumbled, and in World War II, even the United States could barely make enough for Little Boy before August 1945. Especially with 1940s technology, enriching the uranium with Germany's constant shortage of resources would be extremely hard to do and even harder to keep secret. And if the Allies found out, the inevitable air raids would impede the program even more.
But let's assume the Germans get a working bomb. Either they get the gun-type enriched and built successfully, or they somehow luck into a considerably more complicated Fat Man-style implosion device, which requires either plutonium or a smaller amount of HEU than a comparable gun-type. They now have the problem of no viable delivery systems. It's often stated that the B-29 cost as much to develop as the nuclear bomb. This leaves out that the Superfortress was as essential to the A-Bomb as the enrichment plants-it was the only Allied bomber that could even carry a bulky 1940s nuke.
The Germans had no bomber even close (especially if the device was bulkier and less efficient than the actual American ones). About the only sorta-kinda-maybe-a-little-viable aerial delivery method I can think of would be to stuff the device into a lumbering Me 323 Gigante transport and send it on a one-way trip, and that would be as vulnerable as you'd think. It's either that, a similar slow transport against opponents with air superiority, or the limited defensive use of just keeping it on the ground and detonating it when Allied troops came near. Fantasies of nuclear armed V-2s are just those.
Like Sea Lion, the German atomic bomb makes for good fiction. Also like Sea Lion, it has little basis in fact.