Abbreviated NTBT, this 1963 treaty was signed by the U.S., the USSR & the U.K.
... und 
unter Wasser, abgekrzt oft NTBT (Nuclear Test Ban Treaty) oder PTBT (Partial [DOC] [TLE] Debates and authority of the UN Security Council - Rysmun 2015 [PAR] Nuclear Test Ban Treaty (NTBT, 1963) ...