Especially take note of Carey Sublette's comment on the design history in the blog comments: Mr. Sublette is definitely a name to be reckoned with, as far as unclassified nuclear analysis goes. His thought, that the design was basically taken direct from the Thin Man bomb design, is an especially interesting one.
As for why the unclassified world thought what it thought for so long, I always presumed it was because men in the 1940's naturally assumed that the rod moves into the long tube, not the tube moves to surround the rod. (Cut to shot of train going into tunnel.)
Especially take note of Carey Sublette's comment on the design history in the blog comments: Mr. Sublette is definitely a name to be reckoned with, as far as unclassified nuclear analysis goes. His thought, that the design was basically taken direct from the Thin Man bomb design, is an especially interesting one.
As for why the unclassified world thought what it thought for so long, I always presumed it was because men in the 1940's naturally assumed that the rod moves into the long tube, not the tube moves to surround the rod. (Cut to shot of train going into tunnel.)