Sindhughosh-class submarine

INS Sindhuvijay has been upgraded with the hydro acoustical USHUS complex and the CCS-MK radio communications system.^[3] On 29 August 2014, the Defence Acquisition Council (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 ₹4,800 crore (equivalent to ₹77 billion or US$800 million in 2023).^[4] 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.^[5] Scheduled to re-join the fleet on 31 March 2015, she re-entered service on 23 May.^[6][7]

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 ₹5,000 crore (equivalent to ₹72 billion or US$750 million in 2023) 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.^[8][9]

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.^[10][11][12]

As reported on 3 September 2025, INS Sindhuvijay is expected to undergo a refit at the Hindustan Shipyard. While the Navy has acquired the Acceptance of Necessity (AoN) from the Defence Acquisition Council of the Ministry of Defence, the contract finalisation is expected to be completed within two or three weeks. Given that all the procedures are completed on schedule, the submarine is expected to begin its refit by the end of the year. The refits will include hull repair, equipment overhauling, upgrading sensors and weaponry, extending the submarine's life as well as enhancing combat readiness of the vessel.^[13]

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.^[14]

It was reported in April 2023 that India would be purchasing over 20 Klub anti-ship cruise missiles worth $120 million.^[15][16] On 4 February 2025, it was reported that the deal has been concluded for cruise missiles for Sindhughosh-class submarines in the presence of the Defence Secretary Rajesh Kumar Singh.^[17][18][19]

One of the submarine was deployed alongside INS Vikrant along with 7 frontline warships and 5 submarines (Shishumar class and Kalvari class) on 7 November 2024. The operations included carrier operations of MiG-29K, missile firing drills, submarine manoeuvres and flypasts by 30 aircraft demonstrated to the President of India Droupadi Murmu who was present on board INS Vikrant.^[20][21][22]

The lead ship of the class, Sindhughosh, was decommissioned after 40 years of service in Mumbai in the presence of the Western Naval Command chief, Vice Admiral Krishna Swaminathan. The submarine was paid off under the command of Lieutenant Commander Rajat Sharma.^[23]

• 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.^[24]
• 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.^[25]
• On 14 August 2013 an explosion, followed by a fire, was reported to have occurred on Sindhurakshak.^[26] Sindhurakshak sank in the dock.
• On 17 January 2014, Sindhughosh ran aground due to the low tide, while returning to the Naval Dockyard, Mumbai.^[27]
• 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.^[28]

• 
  INS Sindhurakshak
• 
  INS Sindhuvijay
• 
  INS Sindhurakshak at Portsmouth Harbour, UK in 2013
• 
  design of submarines

• List of active Indian Navy ships

Equivalent submarines of the same era

• Harushio class
• Upholder/Victoria class
• Walrus class
• Santa Cruz class
• Hai Lung class