The D-4 submarine launched ballistic missile (SLBM) system,
using the R-21 rocket, used storable liquid-propellants, which
were toxic and corrosive - clearly not the best thing to be
carried in the sealed environment of a submarine. The concept of
the follow-on D-6 system, to be installed on series 629 and 658
nuclear-powered ballistic missile submarines, was to use safer
solid propellants. Decree 1032-492 of 5 September 1958
authorised research and development of the D-6 solid propellant
SLBM system, to be armed with the Article 'R' rocket. The
missile was to have a range of 800 to 2500 km, but the D-6
launcher had to have the same external dimensions as that used
for the D-2/R-13 liquid propellant SLBM. Two propellants were
considered for the rocket: Nylon-B, a double-based ballistic
powder, and Nylon-S, a composite propellant consisting of
ammonium perchlorate, a furfuryl-acetate binder, a titanium
oxidiser developed in the US by Thiokol, and nitroguanidine.
Altogether seven variants of the rocket were stu