A Russian designed older version Kilo class submarine. The export version is known as Project 877EKM by Russia's Rubin Design Bureau. India has 9, known as the Sindhughosh class.
Indian press articles on submarines too often report the Indian Government's vague plans to build X number of nuclear submarines over some indeterminate time period. The article below is different - much more down to Earth. The deal below with Russia could be interpreted as being part of Russia's campaign to sell 6 Amur/Ladas (with AIP and VLS) to India for India's future submarine competition Project 75(I).
Ajai Shukla for India's Business Standard, July 22, 2015 reports http://www.business-standard.com/article/companies/anil-ambani-signs-splashy-russian-joint-venture-for-submarine-overhaul-115072200015_1.html :