Question: The Kh-15 was a missile carried by the supersonic strike bomber operated by what organization?
Sentence (from "R-21 (missile)"): The R-21 (Russian: "Р-21" ; NATO: SS-N-5 'Sark/Serb'; GRAU: 4K55) was a submarine-launched ballistic missile in service with the Soviet Union between 1963 and 1989.
Relevant evidence: No