The Treaty on the Limitation of Underground Nuclear Weapon Tests (Aka-the Threshold Test Ban Treaty (or TTBT)) was signed in July 1974 by the US and the USSR. It establishes a nuclear weapons test blast "threshold," by prohibiting nuclear tests of devices having a atomic yield exceeding 150 kilotons (equivalent to 150,000 tons of TNT). Of particular significance was the relationship between explosive power of reliable, tested warheads and first-strike capability. Agreement on the Threshold Test Ban Treaty was reached during the summit meeting in Moscow in July 1974.