R-27 / SS-N-6 SERB & SS-NX-13

The R-27 / SS-N-6 submarine-launched ballistic missile is a single-stage, storable liquid-propelled missile. Three variants used inertial guidance systems while a fourth variant [the SS-NX-13] used radio command guidance. One of the inertial-guided variants carried multiple re-entry vehicles [MRV] that were not independently targetable. The R-27 and R-27U ballistic missiles with the D-5 and D-5U launch complexes were designed to destroy medium-range strategic targets. Complexes were installed in submarines of 667A and 667AU Projects.

The missile was first seen publicly in a Moscow parade in 1967. By the mid-1970s Western intelligence believed that the SS-N-6 Mod 1 delivered a 1500-1b reentry vehicle to a maximum operational range of 1300 nm with a CEP of about 0.6 nm. The SS-N-6 Mod 2 was believed to deliver a 1,500-lb reentry vehicle to a maximum operational range of 1,600 nm. The SS-N-6 Mod 3 was assessed as having MRV payload consisting of two 600-lb RVs or three 400-lb RVs. Both the Mod 2 and Mod 3 were thought to have a CEP of about 0.7 nm. The yield of the single RV Mod 1 and Mod 2 was believed to be 0.6 to 1.2 MT. The yield of each warhead in the 2-MRV variant of the Mod 3 was estimated at 0.4 to 0.8 MT, and the yield of each warhead in the 3-MRV variant at 0.1 to 0.4 MT. The existence of a 2-MRV variant of the Mod 3 is not reported by Russian sources.

Sixteen of the SS-N-6 missiles were carried aboard the Yankee class nuclear submarine. Missiles could be launched while the submarine was submerged and underway. According to Western estimates, normal reaction time, while the submarine was submerged on patrol, was about 15 minutes. Reaction time under conditions of peak alert is one minute. The allowable hold time under conditions of peak alert was one hour. The Yankee submarine demonstrated a patrol capability of 75 days, and patrols of longer duration (90 days) were believed possible, consistent with crew provisioning and morale.

The R-27 (4K-10) ballistic missile had a single stage and burned liquid propellant. It was the first sea-based liquid-propellant missile in the world. The missile incorporated the following advanced design and engineering solutions used in future for all liquid-propellant missiles:

• all-welded missile body;
• propulsion system is placed inside fuel and oxidizer tanks;
• use of metallized rubber shock absorbers and arrangement of the missile launch elements on its body;
• missile tanks were filled with long-storable components and then encapsulated by the manufacturer;
• automated control of pre-launch operations and volley firing;

These solutions allowed to radically reduce the missile size and minimize its readiness time (time of pre-launch operations - 10 min and time between launches - 8 s), as well as made the system less expensive in operation and more easier to maintain.

One distinctive innovation in this design was the placement of the rocket engines within the fuel tank in order to reduce the external dimensions of the vehicle. The missile body was made of aluminum alloys, and the fuel and oxidizer tanks had common bottoms. The command and control avionics systems were was placed in a hermetically sealed container in the lower interior of the oxidizer tank, eliminating the need for a separate instrument module. Another design innovation was the placement of the command system's sensors on a gyro-stabilized platform. These design features characterize all subsequent liquid-propellant SLBMs developed by SKB-385.

The propulsion system has a single-chamber sustainer and a dual-chamber control engine. The thrust chambers of the attitude control engine were oriented at an angle of 45 degrees from the stabilization axis of the missile (instead of the usual scheme in which the four thrust chambers are aligned along the stabilization axis). Due to an increased thrust ratio the R-26 missile had four times the range of the R-13 missile (2400 km against 600 km) despite its similar launching weight (14.2 versus 13.7 tons).

The rocket carried a monoblock warhead with a thermonuclear charge of 1 Mt, which made it possible to hit an area object confidently.

The missile was loaded in the launching tube with the use of several metallized rubber shock absorbers. Together with the lack of aerodynamic stabilizers, this allowed a significant reduction in the overall dimensions of the launch tube. The missile was fired from a flooded tube. A gas bubble generated by the missile's docking adapter dampened the hydraulic shock caused by engine ignition in the tube.

The designers developed an original design of the tail section for this missile, which contained part of the elements of the launcher. This approach allowed to reduce the mass of the latter by an order of magnitude. In general, both the D-5 missile system and the R-27 SLBM were quite successful. The ship-based missile service system provided automated remote control and monitoring of the state of the systems from a single console, automated control of prelaunch preparation, launching of missiles. The complex routine inspections of all missiles were carried out from the control panel of missile weapons.

The rockets were fired from a depth of 50 m, the prelaunch training time was 8 minutes, and the interval between missile launches was 8 seconds.