1940 May 3 - German troops occupy Norway, seizing the world's only heavy-water production plant at Vemork.
May 19 - Otto Frisch and Rudolf Peierls submit a memorandum to the British government estimating the critical mass of uranium 235 needed for an atomic bomb and urging a bomb research project. More » 1954 April 12 to May 6 - Hearings regarding Oppenheimer's loyalty cause him to lose his security clearance. More » 1957 May 15 - First British H-bomb exploded at Christmas Island in the Pacific. More » 1972 May 26 - President Nixon and General Secretary Brezhnev sign the Anti-Ballistic Missile (ABM) Treaty, the Strategic Arms Limitation Treaty (SALT) and the Interim Agreement on Strategic Offensive Arms, in Moscow. 1974 May 18 - India sets off a low-yield device (8 kilotons) under Rajasthan desert. More » 1976 May 28 - President Gerald Ford and General Secretary Leonid Brezhnev sign the Underground Nuclear Explosions for Peaceful Purposes (PNE) Treaty. More » 1998 May 11 - India conducts three underground nuclear tests, its first in 24 years. One of the tests is a thermonuclear weapon.
May 13 - India conducts two more nuclear tests.
May 28 - Pakistan conducts five nuclear tests in response to India's nuclear tests.
May 30 - Pakistan conducts its sixth nuclear weapons test. The explosion is in the 1 to 5 kiloton range. 2002 May 24 - Strategic Offensive Reductions Treaty is signed between the U.S. and Russia. More » 2008 May 25 - North Korea conducts its second nuclear test. The device's yield is estimated at 2-3 kilotons.