Context: Recently, the Navy’s Kilo-class submarine INS Sindhuratna underwent a major upgrade (Medium Refit Life Certification process) in Russia which extended its life.
About INS Sindhuratna:
- INS Sindhuratna is a Sindhughosh-class diesel-electric submarine of the Indian Navy that was commissioned in 1988.
- The Sindhughosh-class submarines were built in the Soviet Union (now Russia) and were later acquired by the Indian Navy.
- The submarine with its modernised weapon and sensor suite enhances the force level in the Indian Ocean Region.
Main classes of submarines in service with the Indian Navy:
- Sindhughosh-class: Variant of the Russian Kilo-class submarines. E.g., INS Sindhurakshak, INS Sindhuvir, INS Sindhuratna.
- Shishumar-class: Based on the German Type 209 design, these are diesel-electric submarines equipped with advanced systems. E.g., INS Shishumar, INS Shankush, INS Shalki, and INS Shankul.
- Kalvari-class (Scorpène-class): Based on the Scorpène design developed by Naval Group (France). E.g., INS Kalvari, INS Khanderi, INS Karanj, INS Vela, INS Vagir, and INS Vagsheer (yet to be commissioned).
- Arihant-class: India’s indigenous nuclear-powered ballistic missile submarines (SSBNs). Currently, INS Arihant is the only operational submarine of this class. The second in the series, INS Arighat, is in the final stage of sea trials. These submarines are equipped with nuclear propulsion and are capable of carrying ballistic missiles.
- Chakra-class: Nuclear-powered attack submarines leased from Russia. Currently, INS Chakra-II, the submarine of this class, is in service with the Indian Navy. Chakra-III is expected to be delivered to the Indian Navy by 2025.

Project 75:
- Project 75 includes the indigenous construction of six Kalvari-classScorpene submarines developed by the Naval Group- a French defence major and the Spanish state-owned entity Navantia.
- The submarines are being constructed at Mazagon Dock Shipbuilders Limited (MDL) Mumbai in collaboration with Naval Group.
- The submarines are INS Kalvari, INS Khanderi, INS Karanj, INS Vela and INS Vagir (already commissioned into the Navy) and INS Vagsheer (under sea-trail) was launched in April 2022.
- This class of submarines have Diesel Electric transmission systems and are attack submarines or the ‘hunter-killer’ type which are designed to target and sink adversary naval vessels.
- They have the capability of operating in a wide range of Naval combat including anti-warship and anti-submarine operations, intelligence gathering and surveillance, and naval mine laying.
Project 75-I:
- Project 75-I is distinct from Project 75. Project 75-I seeks to acquire submarines with more advanced capabilities to meet evolving maritime challenges and technological advancements.
- Project 75-I is an initiative by the Indian Navy to acquire six conventional, diesel-electric attackadvanced submarines for its fleet. The advanced capabilities include air-independent propulsion (AIP), ISR, special operations forces (SOF), anti-ship warfare (AShW), anti-submarine warfare (ASW), anti-surface warfare (ASuW), land-attack capabilities and other features.
- Air-independent propulsion (AIP) systems allow submarines to remain submerged for longer durations without the need to surface, and thus, significantly enhance the operational endurance and stealth capabilities of submarines.
The project aims to build these submarines under the strategic partnership model, which involves collaboration between Indian shipyards and foreign original equipment manufacturers (OEMs).