Treaties are between the United States and Russia.
Test Ban Treaty, which prohibits above-ground and underwater testing of nuclear weapons, the United States and the Soviet Union were relegated to conducting all nuclear weapons test underground, though the Treaty did not set any limit on the numbers of yields of UGTs. In 1974, the United States and Union of Soviet Socialist Republic agreed to pursue the possibility of further limiting nuclear weapons testing and in July of 1974, agreed on a treaty and verification protocol that limited UGTs to no greater than 150 kt. Although the technical difficulty associated with both sides recognized verification of a threshold treaty, the 150 kt threshold effectively limited the fielding of nuclear weapons based on new designs whose yields were much greater than 300 kt. Though the United States had terminated its PNE program in 1973, the Soviet Union continued an active PNE program ostensibly for oil and gas storage. In negotiating the TTBT, both Parties recognized the need to establish a similar agreement to govern the conduct of PNEs.