INS Sindhurakshak (Sanskrit, for Protector of the Seas)[3] was a Russian-made Kilo-class 877EKM[4][5] (Sindhughosh-class) diesel-electric submarine of the Indian Navy.

[7] On 4 June 2010, the Indian Defence Ministry and Zvezdochka shipyard signed a contract worth US$80 million to upgrade and overhaul the submarine.

[8] The submarine suffered a major fire and explosion on 14 August 2013 and sank at Mumbai's naval dockyard with the death of 18 crew members.

The submarine was modernised, repaired and retrofitted under Project 08773, and after the upgrade, the sea trials started in October 2012.

[17][20] The Club-S (3M54E1 anti-ship and 3M14E land attack) missiles, USHUS sonar, СCS-MK-2 radio communication systems and Porpoise radio-locating radar, and other safety-enhancing features were incorporated.

An emergency call was placed via the Indian Ministry of External Affairs to the Egyptian Navy, which sent its latest tugboats and towed the submarine to Port Said.

[24][25] On 14 August 2013, the Sindhurakshak sank after explosions caused by a fire on board when the submarine was berthed at Mumbai.

Navy divers were also brought in as there was a possibility that 18 personnel were trapped inside and Defence Minister A. K. Antony confirmed that there were fatalities.

[20] Due to the explosion, the front section of the submarine was twisted, bent and crumpled, and water had entered the forward compartment.

[43] In December 2014, a naval court of inquiry arrived at the preliminary conclusion that human error as a result of crew fatigue caused the disaster.