Close, but no cigar

The only known German diagram of a nuclear weapon.

Eventually the passage of time tends to reveal materials that can confirm previous suspicions. Lots of foot work, arm bending, and a desire by archivists to reveal materials and shed some new light on the probability that Germany during the World War II era was developing, and some contend test, a nuclear weapon.

"New light on Hitler's bomb"

Here are some thoughts by Hans Bethe regarding Germany and the nuclear bomb.

"The Farm Hall tapes show that Werner Heisenberg did not know how to calculate the critical mass in 1945, indicating that he did not work on atomic bombs during the war."

"The German Uranium Project"

NOVA aired Hitler's Sunken Secret some time ago. I guess its focus was on the discovery of a ship containing canisters of "heavy water"--deuterium:

One of the most daring clandestine operations of World War II was the 1944 sinking of the Norwegian ferry Hydro with its cargo of "heavy water" destined for the Nazi's secret atomic bomb project. Although the mission was declared a success, no one ever established if the special shipment was actually on board. In this program, NOVA plunges 1,300 feet beneath a remote Norwegian lake to find the answer.

Exploring the pristine lake bottom with a remotely operated vehicle, the expedition team locates the remarkably well-preserved ship, along with evidence of a mysterious cargo in steel drums. Analysis of the contents of one of those drums will solve a six-decade-long mystery about the role the Allies played in preventing a Nazi nuclear bomb.
The program features participants in the Hydro affair, including a member of the Norwegian Resistance who slipped aboard the vessel on the night of February 21, 1944, and helped plant explosives in the bow that were timed to go off the following day when the ferry was over the deepest part of Lake Tinn. Intelligence had indicated that the Hydro would be transporting railroad flatcars loaded with barrels of heavy water produced by the nearby Norsk hydroelectric plant, which at that time was the world's largest power station. The Germans had conquered Norway early in the war and immediately ordered the Norsk plant to double its output of heavy water.

Crucial to the Nazi nuclear program, heavy water was extracted from ordinary water by using electricity to break apart ordinary water molecules and concentrating the solution until all that remained was the rare, heavier form of the liquid. With a bigger, "heavier" nucleus than ordinary water, heavy water was an ideal substance for slowing neutrons in a nuclear reactor, a key step in triggering a chain reaction....

With a sufficient supply of heavy water and uranium, the Germans could use reactors to produce bomb-grade material for nuclear weapons that would render the Third Reich invincible. Fear of that outcome sparked the Allies to undertake their own crash program. This became the Manhattan Project, which ultimately produced the first atomic bomb.
The Norwegian partisans had no inkling of the reason for their mission. All they knew was that it had top priority from their contact in London and that innocent Norwegian civilians were likely to be aboard on the last, fatal voyage of the Hydro. ...
NOVA interviews one of the civilians who survived the sinking and who remembers seeing barrels floating among the debris. These barrels were immediately recovered by the Germans and shipped to Berlin. However, had they been filled with heavy water they should have sunk, not floated. This is just one of the mysteries NOVA solves by snaring a barrel, bringing it to the surface, and seeing just what's inside.

Transcript:

Hitler's Sunken Secret

NOVA's Hitler's Sunken Secret was better than I expected: A bit of science; a bit of mystery. It was a decent description of Germany's attitude towards the production of nuclear weapons--again, money politics, war strategy. Their discovery of fissionable characteristics of uranium was known in the late '30's and they were in need of the moderating quality of deuterium--lots of it to meet the qualifications of weapons grade plutonium production. The appropriated Norwegian fertilizer plant was used to supply the deuterium and a shipment was to be sent to Germany via the ferry across a Norwegian lake. Well, intelligence reports were somewhat colored and the full scope of Germany's attitude towards nuclear weapon production was not fully understood, thus the order was given to sink the ferry. It was successfully sunk with the loss of lives to boot. But the curiosity of historians wanted to make certain of the existence of drums of deuterium and answer a few mysterious questions. The ferry was found and one drum was brought to the surface for analysis. Sure enough, it was filled with deuterium which even matched the manifest records. But the curious question...why was there no German security around and on board the ferry? The answer was revealed in the politics and war strategy of Germany--a simple matter of not really realizing the long range value of nuclear weapons for a militaristic country as Germany. Quicker solutions were necessary for them. In other words, the production of nuclear weapons was a low priority for them and the extra security was not needed. And, there was sufficient science in the program too: Cursory explanation of nuclear weapon manufacture, physics of fission, and chemistry. It is worth viewing a second time.

And Japan?

"Nuclear Weapons History: Japan's Wartime Bomb Projects Revealed"