On this day 49 years ago, on May 28, 1976 (April 30, 1976 lunar calendar), the US-Soviet Treaty on the Peaceful Use of Underground Nuclear Explosions was signed. On May 28, 1976, US President Ford and General Secretary of the Central Committee of the Soviet Communist Party Leonid Brezhnev signed the US-Soviet Treaty on the Peaceful Use of Underground Nuclear Explosions in Washington and Moscow respectively, and signed an Additional Protocol. The treaty has a valid period of 5 years, which can be extended for 5 years after expiration. The treaty stipulates that the contracting parties may conduct peaceful nuclear explosions of less than 150,000 tons in any place outside their respective jurisdiction or control of the test sites stipulated in the treaty, and may also conduct, participate in or assist in peaceful nuclear explosions of less than 150,000 tons in the territory of other countries at their request. However, the contracting parties shall not conduct a single peaceful nuclear explosion with a yield of more than 150,000 tons, nor a combined peaceful nuclear explosion with a total yield of more than 1.50 million tons; the party conducting the peaceful nuclear explosion must provide the other party with detailed information before and after the event. The United States and the Soviet Union have been unable to ratify the treaty.