Frederick Forsyth - The Fourth Protocol

he title refers to the 1968 Nuclear Non-Proliferation Treaty, which (at least in the world of the novel) contained four secret protocols. The fourth of the protocols was meant to prohibit non-conventional deliveries of nuclear weapons, i.e. by means other than being dropped from aircraft or carried on ballistic missiles. This included postal delivery or being assembled in secret, close to the target, before being detonated.