The Delta III-class submarine, Soviet designation Project 667BDR Kaľmar (Squid), is a large ballistic missile submarine operated by the Russian Navy. Like other previous s, the Delta III class is a double hulled design, with a thin low magnetic steel outer hull wrapped around a thicker inner pressure hull. Design The technical description and requirements for a new ballistic missile submarine were published in 1972. Development of Project 667BDR was begun at the Rubin Central Design Bureau for Marine Engineering under the direction of main designer Sergeiy Nikiticz Kovalev (Сергей Никитич Ковалёв). The submarine was to be a successor to the project 667BD. The Delta III-class submarines are significantly quieter and have a higher missile section for newer, longer-ranged missiles. The hull is divided into ten waterproof sections. The first, third, and tenth sections are emergency sections with escape hatches and transverse struts added to increase pressure resistance. A new modular freon firefighting system was installed. A solarium and gymnasium were to be installed to improve living conditions. The main propulsion system, OK-700A, consists of two pressurized water reactor VM-4S (2×90 MW) with two steam turbines giving to two five-bladed, fixed-pitch shrouded propellers with improved hydro-acoustic characteristics. Two back-up TG-3000 turbogenerators were also installed. Average period between refuelling and overhaul is about ten years. The Delta III class are fitted with a new sonar system, the MGK-400 Rubikon (in submarine K-424, the older MGK-100 Kerch was installed), developed under the leadership of main designer S.M. Shelechov. The Rubikon can operate in infrasound frequencies, and contains automated systems for target classification. Its maximum range in ideal hydrologic conditions is about . The Delta III class are equipped with a new battle management system, the Almaz-BDR (or MVU-JZBDR) torpedo fire control. For improved stealthiness, a new inertial navigation system, Tobol-M-1 (on newer ships Tobol-M-2), with higher accuracy, was installed. Tobol-M works with data from two observatories which are saved for two days, and also contains a hydro-acoustic navigational station (Shmeľ or "Bumblebee"), which allows the submarine to determine its position from hydro-acoustic buoys. The Delta III class includes the Molnija-M communications system, with satellite capabilities provided by the Tsunami subsystem. In February 1973, State Rocket Center Makayev began development of a new two-stage liquid-fueled ballistic missile R-29R (3M40, RSM-50, SS-N-18). Improvements in the R-29R over the original R-29 include MIRVed capability and upgraded inertial navigation system with satellite-assisted navigation, giving the new