All Delta III-class submarines passed general overhaul refuelling and upgrade in Zvezdochka shipyard, Severodvinsk, or in Zvezda shipyard, Bolshoy Kamen, since 1991, when the Soviet Union collapsed. An upgraded missile system, D-9R, with lightly modified R-29R missiles, was delivered from 1987 to 1990. On some ships the sonar station "Avrora-1" was installed.