Duct matching

On February 10, 1955, John Cockcroft received a diplomatic letter attaching a translated Soviet article about that nation’s first “peaceful” (though it wasn’t) reactor at Obninsk (that location only got clarified later). Cockcroft handwrote to his technical guru, John Dunworth: “Do Reactor Physics have any views on this?” Dunworth’s handwritten response is hard to decipher but begins thus: “It looks like a pressurized water device. The duct in the middle photo strongly correlates…” Dunworth was wrong, Obninsk was not at all a Pressurized Water Reactor.

First UK knowledge of Obninsk reactor
Snelling, R. W. 1955. Snelling to Cockcroft, Feb. 10, 1955. AB 6/1659. National Archives, Kew, United Kingdom.