RDS-6s
The Soviet Union detonates its first hydrogen bomb, code named RDS-6s, in its first thermonuclear weapons demonstration. The bomb is estimated to have a yield of 400 kilotons, thanks to a layered design devised by nuclear physicist (and later political exile) Andrei Sakharov, though Sakharov’s design is incapable of being scaled up, ending its use in later Soviet nuclear weapon designs.