United Kingdom

After the end of World War II, the United States decided to closely guard its nuclear weapon technology, even from the Allies. The country that felt the most hurt and bitter by the American attitude was Britain. The UK and the US had solid war-time cooperation on atomic energy, illustrated most notably by the agreements at Hyde Park in 1942 and Quebec in 1943. London felt entitled to information on how to manufacture the bomb due to those wartime agreements. Much to the UK’s chagrin, the American Congress passed the McMahon Act of August 1946, which outrightly prohibited any kind of American atomic cooperation with any nation. That also included its close transatlantic ally, Britain. The guarded attitude by the US towards sharing nuclear technology and technological wherewithal with any other nation was “shaped by their desire to first put in place a mechanism of international control acceptable to both the American president and Congress” as well as to international allies and adversaries. 1