Nuclear weapons had been invented and used by the USA and in 1949 the Soviet Union produced its first atom bomb, followed by Britain in 1952.
Roedd arfau niwclear wedi eu dyfeisio a’u defnyddio gan yr Unol Daleithiau ac ym 1949 cynhyrchodd yr Undeb Sofietaidd ei fom atomig cyntaf, ac fe’i dilynwyd gan Brydain ym 1952.