Quebec Agreement 1943
British scientists carried out important work as part of the British contribution to the Manhattan Project, and in July 1945 British authorization to use nuclear weapons against Japan was granted. Hyde Park Aide-Mémoire, in September 1944, extended Anglo-American cooperation to the post-war period, but by the end of the war American enthusiasm for the alliance with Britain had diminished. The McMahon Act ended technical cooperation by controlling “limited data.” On January 7, 1948, the Quebec Agreement was replaced by a modus vivendi, an agreement that allowed for a limited exchange of technical information between the United States, Great Britain and Canada. The departure of Igor Gouzenko and the resulting espionage conviction of Alan Nunn May, a British physicist who worked at the Montreal laboratory, prevented American officials from exchanging information with the United Kingdom.  Congress, which was unaware of the existence of Hyde Park Memory Aid because of the loss of the American copy, passed the McMahon Act.  Signed by Truman on August 1, 1946 and came into force at midnight on January 1, 1947, this Act ended technical cooperation. Its control over “limited data” prevented U.S. allies from obtaining information.  Other scientists were denied access to the documents they had written a few days earlier.  The McMahon Act fuelled resentment of British scientists and officials and led directly to the British decision of January 1947 to develop its own nuclear weapons.  In the United States, the British veto on the use of nuclear weapons was all the rage when, on May 12, 1947, the Joint Atomic Energy Committee was informed of the Quebec Agreement (but not of the November 1945 agreement) , which led to strong pressure on Truman to abandon the provision.  On January 7, 1948, Bush, James Fisk, Cockcroft and Mackenzie reached an agreement, known as modus vivendi, that allowed the limited exchange of technical information between the United States, Great Britain and Canada, which officially rewrote the Quebec agreement.   Like the Quebec agreement it replaced, the modus vivendi was classified as “Top Secret”.
 The 1943 Quebec Agreement dealt with the atomic bomb. The U.S. government`s decision to continue work on a hydrogen bomb was not made until 1950. When the agreement was reached, we obviously did not know whether the hydrogen bomb would ever become a reality. asked the Prime Minister whether he would issue a white paper containing the corresponding correspondence on the end of his secret agreement with President Roosevelt. It was clear that the elimination of Italy from the war was the allies` main priority; This was to be done by the end of 1943. After that, there was the next hope that Germany would be defeated in the autumn of 1944, which would only keep Japan among the Axis powers.  I would like to ask the Prime Minister if it was not a fact that it was better to keep knowledge of this matter in the hands of a few people and that the war cabinet was informed that there had been discussions and agreements with the 962-member government on this matter, but that they were not. Indeed. to know more about the details, or what the agreement was, but simply that an agreement had been reached, and the case rested there? Bush was in London on July 15, 1943 to attend a meeting of the Anti-U-Boat Committee of the British War Cabinet.
Sir Stafford Cripps took him to Churchill, who told Bush that the president had given him his word of honour on full cooperation and that he was outraged by the obstruction of American bureaucrats. Bush proposed that the matter be settled with Stimson, who was also in London.