|Preceded by:||Vela class|
|Succeeded by:||Kalvari class|
|Length:||72.6 m (238 ft 2 in)|
|Beam:||9.9 m (32 ft 6 in)|
|Draught:||6.6 m (21 ft 8 in)|
|Test depth:||300 m (980 ft)|
|Complement:||53 (13 Officers)|
Sindhughosh-class submarines are Kilo-class diesel-electric submarines in active service with the Indian Navy. Their names are in Sanskrit, but in their Roman-alphabet forms sometimes a final short -a is dropped.
The submarines have a displacement of 3,000 tonnes, a maximum diving depth of 300 meters, top speed of 18 knots, and are able to operate solo for 45 days with a crew of 53. The final unit was the first to be equipped with the 3M-54 Klub (SS-N-27) antiship cruise missiles with a range of 220 km.
Life extension and refit
INS Sindhuvijay has been upgraded with the hydro acoustical USHUS complex and the CCS-MK radio communications system. On 29 August 2014 DAC cleared the long-awaited mid-life upgrade of the four Kilo-class submarines, which would be carried out in Indian shipyards and is likely to cost Rs. 4,800 crore (4,800 million). On 5 November 2014 official sources at HSL said more than 90% of the work has been completed on the seventh submarine of the Sindhughosh class INS Sindhukirti. Scheduled to re-join the fleet on 31 March 2015, she re-entered service on 23 May.
The Indian Navy signed a contract with the Russian shipbuilder Sevmash to refit and upgrade the existing submarines and to extend their operational life by 35 years. The first submarine, INS Sindhukesari, will be sent for refit starting June 2016. 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 and fitted with Klub land attack cruise missile.
In 2015, the naval exercise Malabar, between the navies of India and the United States, involved Sindhudhvaj and USS City of Corpus Christi hunting each other. India Today reported that Sindhudhvaj managed to track Corpus Christi and score a simulated kill without being detected.
In December 2015, L&T was chosen by the Russian shipbuilder Sevmash to be its Indian partner in the refit project. While the first of the four Kilo class subs will go to the Russian Zvezdochka shipyard for inspection and refit, the remaining three are likely to be modernized at the Kattupalli shipyard. The first of the submarines to be modernized at private yard, a first for India, will go in by 2017, An order for 2-3 more submarines could also be commissioned, depending on ongoing acquisition plans of the Indian Navy.
- On 10 January 2008, INS Sindhughosh collided with the cargo ship MV Leeds Castle. The submarine was reported to have sustained superficial damage to its conning tower. As a result, the submarine was out of service for a month. The cargo ship was in restricted shallow waters.
- On 26 February 2010, a fire on board INS Sindhurakshak killed one sailor and injured two others. The fire was due to a defective battery.
- On 14 August 2013 an explosion, followed by a fire, was reported to have occurred on Sindhurakshak. Sindhurakshak sank in the dock.
- On 17 January 2014, Sindhughosh ran aground due to the low tide, while returning to the Naval Dockyard, Mumbai.
- On 26 February 2014, smoke was detected on board INS Sindhuratna resulting in 7 sailors being rendered unconscious and two dead. Those unconscious were airlifted to hospital 
Ships of the class
|Name||Pennant||Builder||Homeport||Commission date||Decommision date||Status|
|Mumbai||30 April 1986||Refitted to project 08773 2002-2005 at Zvezdochka shipyard|
|Sindhudhvaj||S56||Sevmash||Mumbai||12 June 1987||To be Refitted to project 08773|
|Sindhuraj||S57||Sevmash||Mumbai||20 October 1987||To be Refitted to project 08773|
|Sindhuvir||S58||Sevmash||Mumbai||26 August 1988||Refitted to project 08773 1997-1999 at Zvezdochka shipyard|
|Sindhuratna||S59||Sevmash||Mumbai||22 December 1988||Refitted to project 08773 2001-2003 at Zvezdochka shipyard|
|Sindhukesari||S60||Sevmash||Vishakhapatnam||16 February 1989||To be Refitted to project 08773|
|Sindhukirti||S61||Sevmash||Vishakhapatnam||4 January 1990||Refitted to project 08773 from 2007-2015 in her home base Vishakhapatnam|
|Sindhuvijay||S62||Sevmash||Vishakhapatnam||18 March 1991||Refitted to project 08773 2005-2007 at Zvezdochka shipyard|
|Sindhurakshak||S63||Sevmash||Mumbai||24 December 1997||5 September 2017||Refitted to project 08773 09.08.2010-2012 at Zvezdochka shipyard.|
Exploded and sank in Mumbai 14 August 2013
|Sindhurashtra||S65||Sevmash||Vishakhapatnam||19 July 2000||To be Refitted to project 08773|
INS Sindhurakshak at Portsmouth Harbour, UK in 2013
- Russian shipyard to float upgraded Indian Navy Kilo class submarine
- Sen, Sudhi Ranjan (29 August 2014). "Modi Government Drops Rs 6000-Crore Foreign Chopper Plan, Wants 'Made in India'". NDTV.
- "Even Hudhud could not stop INS Sindhukirti refit at HSL". 5 November 2014. Archived from the original on 6 November 2014. Retrieved 5 November 2014.
- "Russia delayed sub refit to weaken shipyard?". Business Standard. 2 September 2014. Retrieved 8 September 2014.
- "Navy gets INS Sindhukirti back". Business Standard. 23 May 2015. Retrieved 24 May 2015.
- "Navy signs Rs 5,000 crore pact with Russian shipbuilder Sevmash for Kilo class submarine refit - The Economic Times". The Economic Times. Retrieved 11 February 2016.
- "Russia to modernize Sindhukesari submarine for the Indian Navy". in.rbth.com. Retrieved 11 February 2016.
- "In underwater battle, India 'annihilates' American n-submarine". India Today. 28 November 2015.
- "Upgrading Kilo class submarines: L&T set to partner Russia for Rs 5,000-crore defence deal - The Economic Times". The Economic Times. Retrieved 11 February 2016.
- "L&T partners with Russia for upgrading Kilo class submarines". Business Insider. Retrieved 11 February 2016.
- "L&T shortlisted for 'Kilo' upgrade work". www.janes.com. Archived from the original on 15 January 2016. Retrieved 11 February 2016.
- News report on Submarine collision
- Fire Mishap on INS Sindhurakshak Archived 2010-03-04 at the Wayback Machine
- "Indian submarine hit by explosion at Mumbai port". BBC News. 14 August 2013. Retrieved 14 August 2013.
- "Submarine hits ground due to low tide, no casualty". 19 January 2014. Retrieved 27 February 2014.
- "Two officers died in fire on board submarine INS Sindhuratna, confirms navy". NDTV News. 27 February 2014. Retrieved 27 February 2014.