 Macmillan's previous attempt to create an agreement at the May 1960 summit in Paris had collapsed due to the 1960 U-2 incident.He was a force in the negotiations leading to the signing of the 1963 Partial Test Ban Treaty by the United Kingdom, the United States and the Soviet Union.He sent Lord Hailsham to negotiate the Test Ban Treaty, a sign that he was grooming him as a potential successor.