The Project 667BDRM “Delfin” (Dolphin) strategic submarine, known in the West as the Delta-4, first entered service in 1985. The Delta-4 and its predecessors (the Delta-1, Delta-2, and the Delta-3 submarines) formed the backbone of the Soviet strategic fleet. The Delta-4 is designed to carry out strategic strikes on naval bases and military installations.
The submarine has a double-hull configuration, and is equipped with 16 missile silos specially designed for the R-29RMU (SS-N-23 Skiff) Sineva ballistic missiles. These missiles are equipped with 4-10 warheads and have a range of up to 8,300 km. The Delta-4 can launch these missiles at depths of up to 55 meters and while moving at a speed of up to 6-7 knots. The Delta-4 is also equipped with four 533 mm torpedo tubes that can fire a variety of different torpedoes. The Delta-4 can also fire the RPK-2 Viyuga (SS-N-15 Starfish) anti-ship missiles from its torpedo tubes. The RPK-2 missiles a have a range of up to 45 km. In total, up to 18 torpedoes or missiles can be carried in the torpedo compartment. In 2011, an upgraded version of the R-29RMU Sineva, dubbed the R-29RMU2 Liner, was introduced for the Delta-4. This new missile is more survivable against anti-ballistic missiles than its predecessor.
The Delta-4 has a maximum speed of 24 knots (regardless of whether it’s surfaced or submerged), and an endurance of about 80 days. The Delta-4 can dive to a maximum depth of 400 meters and has special hydroplanes attached to the sail to break through ice. There are currently 7 Delta-4 submarines in service with the Russian navy. Although these submarines are supposed to be replaced by the Borei class submarines, the latter are entering service very slowly, so the Delta-4 submarines remain in service. Four are equipped with upgraded Sineva missiles, one had its missile silo’s removed and is used as a special purpose platform, and one was damaged by a fire on December 29th, 2011, and is expected to be back in service in 2014.
Photos taken from here.