Were designed to destroy medium-range strategic targets. Installed aboard 667A and 667AU submarines carrying 16 missiles. The D-5 complex was put into operation by the Navy in 1968, and D-5U, in 1974.

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

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

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 operation and maintenance easier and less expensive. The enhanced D-5U/R-27U system was derived from its predecessor, D-5/R-27. Unlike R-27 the R-27U missile was equipped with two types of warheads: single and multiple (cluster) with 3 reentry vehicles. The firing range for a single warhead was increased to 3000 km, while that for a multiple one remained 2500 km.

Basic characteristics
Mass, t: takeoff maximum throw	14.2 0.65
Maximum firing range, km: R-27 R-27U	2500 up to 3000
Type of warhead: R-27 R-27U	single single and multiple
Guidance	inertial
Missile length, m	9.0
Missile diameter, m	1.5
Propellant	liquid