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 studied, two using Nylon-B, and five using Nylon-S. Nylon-B had a specific energy of 40 kg/kW-cm, and a specific impulse of 200 seconds. The motors were built in diameters of 0.70 to 0.85 m, and four motors were clustered per stage. Hydraulic gas vanes were used to steer the rocket. Nylon-S had a specific impulse of 200 seconds, and variants were studied using gas vanes, steerable nozzles (made of composite plastics and molybdenum, or chrome steel).
The draft project was completed in November 1959, and flight trials were to commence in 1960. At Rzhevsk Field and Leningrad test motors of up to 500 kg mass were tested. At the end of 1959 the draft project for the 629D6 launch container for the the series 629 submarine was issued by Ya E Yevgrafov. All drawings were released to Factory 444 for start of construction in December 1960.
Based on the findings of tests on the P5D-4 test stand, decree 38-145 of 18 March 1959 ordered construction of a new test stand for D-6 development. During the course of 1960 the technical project for the P5D-6 test stand for mock-up trials of the missile and container-launcher was completed.
The 613D6 derivative of the 613 nuclear submarine was developed for naval tests of the missile. The decree 141-64 of 9 February 1959 called for design of this submarine to be completed by November 1960. In January 1961 construction of four submarines of this series began at Factory 444.
Decree 656-267 of 18 June 1960 called for further development of the D-6 using Nylon-S propellant for submarine series 629, 658, and 667, the submarines to be designed by Chief Designer A S Kassatsiev. The technical projects for these boats were to be completed by the fourth quarter 1962. Flight trials of the 1100-km range missile aboard a 629B test boat in the third quarter of 1962.
A variant of the rocket was also considered for mobile Army use. It was also planned to replace the liquid-propellant D-4 in the 667 SSBN's with the D-6.
The nuclear device in either missile was to have a mass of 500 kg and a variable yield of from 300 kt to 1.0 MT. The inertial navigation system was to be designed by Semikhatov at NII-592. The missiles would be cold launched from the submarine, igniting above the surface - the Nylon-B version at 30-50 m altitude, and the Nylon-S version at 40-80 m. Two different re-entry vehicles would be used to, that of the Nylon-B version being 1.8 m long.
All of these plans came to a halt on 27 April 1961 when the D-6 was cancelled in favour of the D-7 system, which was to use an RT-15M derivative of the land-based 8K96 solid propellant missile being planned by Korolev. At the time of cancellation, the test stand at Factory 444 was 47% complete. D-6 technology was however used in Korolev's RT-1 test missile, including engines from NII-125.