INS Sindhugosh and INS Sindhuvijay have already been equipped with the Club-S cruise missile systems.
The upgrade wasn't smooth. After INS Sindhuvijay was upgraded, six test firings of the Club-S missile in 2007 failed and India refused to accept the submarines which spent two years in Russia. The technical glitches were eventually sorted out.
The Zvezdochka shipyard will install Club-S cruise missile systems on four Kilo class diesel submarines in service with the Indian navy in the next five years.
"The new missile system will be installed on the INS Sindhuratna, INS Sindhuraj, INS Sindhushastra, and INS Sindhuvir. The retrofit will be carried out at Indian shipyards," the shipyard in northern Russia said in a statement in September 2009.