Paperclip continued to deliver German scientists, engineers, and technicians to the United States for years past the end of WWII. One of the most important of these was Friedwardt Winterberg, who was brought to America before the ink was dry on his PhD in 1955. Winterberg is important because his doctoral supervisors were the wartime nuclear physicists Werner Heisenberg and Kurt Diebner, the latter of whom was much more important than the former.
Winterberg's career looks respectable if not particularly noteworthy at first glance; he spent his working years at the University of Nevada - Las Vegas as a physics professor. But it is in his writing that you get major clues as to what wartime German nuclear science was really up to. Winterberg's books explore various means of provoking nuclear detonations, often with an emphasis on prompt fusion, or fusion in synergy with fission, rather than fission alone. Most modern nuclear weapons incorporate this concept, broadly speaking, but what I am getting at here is a particular concept known as a "Prandtl - Meyer hydrogen bomb". This bomb design utilizes shock waves as described in earlier investigations of how those behave in water (hydrodynamics). It appears very likely that wartime SS scientists, most of them Austrian, attempted to build a megaton class hydrogen bomb based on Prandtl - Meyer principles rather than the Soviet "sloika" or the later US Teller - Ulam configuration. There is fragmentary but consistent information about this in the most recently discovered archival documents.
By far the best and most thorough investigation into the WWII German nuclear weapons program is "Forgotten Creators" by former MIT and US Navy scientist Dr. Todd Rider. The author spent nearly a decade digging through public and private archives and libraries and many hundreds of original WWII papers that had never seen the light of day since the end of the conflict were published for the first time (this was in 2019). The book is more properly a survey of the totality of German science since the 19th century, but a significant portion---around 1,000 pages---deals specifically with the German nuclear effort.
You can download it here: https://riderinstitute.org/revolutionary-innovation/ There are also links to several video presentations the author made in 2022 to various entities such as the Smithsonian and the Hidden History Podcast with D. Ray Smith, the former lead historian at Oak Ridge National Laboratory.
For the Japanese program---which was directly linked to the German version by late in the war if not all the way through---Robert K. Wilcox's book, "Japan's Secret War" is the best resource. The third and final edition of this work also appeared in 2019. It contains some of the findings of a former USAF, CIA, and DIA intelligence officer named Dwight Rider (perhaps a distant cousin of the "Forgotten Creators" author) who had more than 13,000 NARA documents in his possession at the time of his death, all of them having to do with the WWII Japanese atomic bomb. Around 400 original wartime papers are cited in "Secret War".
Several here have mentioned Richard Rhodes and his book, "The Making of the Atomic Bomb". Although Rhodes was a very good author and his research was quite thorough within the bounds of the documentation then available to the public, his book is now unfortunately well behind the latest archival findings. Credit where credit is due: he was one of the barest handful or Western writers to give any kind of proper credit to WWII Japanese nuclear science. But he missed both the German effort and the overall Axis cooperation on WMD's by a wide margin simply because he did not have access to the original wartime documents that were finally declassified at the 50 year mark past the end of the conflict, that is in 1995. Suzuki's disclosures were crucially important to a proper understanding of what was really going on during the war: a frantic race among all of the major powers to weaponize the atom and develop both practicaly weapons and the means of delivering them on target.
Winterberg's career looks respectable if not particularly noteworthy at first glance; he spent his working years at the University of Nevada - Las Vegas as a physics professor. But it is in his writing that you get major clues as to what wartime German nuclear science was really up to. Winterberg's books explore various means of provoking nuclear detonations, often with an emphasis on prompt fusion, or fusion in synergy with fission, rather than fission alone. Most modern nuclear weapons incorporate this concept, broadly speaking, but what I am getting at here is a particular concept known as a "Prandtl - Meyer hydrogen bomb". This bomb design utilizes shock waves as described in earlier investigations of how those behave in water (hydrodynamics). It appears very likely that wartime SS scientists, most of them Austrian, attempted to build a megaton class hydrogen bomb based on Prandtl - Meyer principles rather than the Soviet "sloika" or the later US Teller - Ulam configuration. There is fragmentary but consistent information about this in the most recently discovered archival documents.