NEW DELHI: The Indian Navy is looking to squeeze some more life out of its two decade old kilo class submarines , signing up a contract with Russia to extend the service life of the boats to 35 years. Struggling with a depleted underwater fleet, the Navy has finalized a contract with Russian shipbuilder Zvezdochka and will be sending the first submarine for the refit in June next year.The extensive refit, the value for which is pegged at Rs 5,000 crore for a total of four submarines, will not only extend the life of the boats but will also upgrade their combat potential. Sources told ET that the first submarine to be sent is the INS Sindhukesari that will be fitted with Klub land attack cruise missile.While the first of the four submarines will be upgraded atSeverodvinsk in Russia, the plan is to upgrade the remaining three in an Indian yard as part of the ' Make in India ' initiative. Zvezdochka, which is the Russian yard tasked with the modernization process, has already tied up with Reliance Defence to upgrade the submarines at the Pipavav yard in Gujarat.However, the Navy has currently awarded the upgrade contract for the first submarine only. A decision on the remaining will be taken after a review of Indian yards and their capability to undertake the complex upgrade. The Sindhukesari will be the first of the Indian Kilo class submarines to undergo the life extension upgrade to 35 years even though the Russian Navy has done this 'second refit' to its fleet.Sources told ET that the Sindhukesari, which got its first refit in 1999-2001, will also be fitted with several Indian systems, including navigational and communication equipment. "The idea of a second mid-life refit of Indian submarines has been discussed between Russia and India since 2010. The process of up gradation will take a little over two years," officials told ET.