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India’s Submarine Capability: A Review

A review of India’s present and future submarine capability as the DRDO declared successful user trials of the fuel cell based AIP would reveal necessity for accelerating the 75 (I) programme for the Indian Navy to continue to retain a submarine advantage in the Indian Ocean Region by end of the decade.

Why Now?

India’s Defence Research and Development Organisation (DRDO) announced successful conduct of Fuel Cell based Air Independent Propulsion (AIP) User Specific Tests on March 08. “The plant was operated in endurance mode and max power mode as per the user requirements,” said the Press release of the Ministry of Defence.

The AIP based system is being developed by Naval Materials Research Laboratory (NMRL) of DRDO.

Explaining the importance of the AIP the release said, “AIP has a force multiplier effect on lethality of a diesel electric submarine as it enhances the submerged endurance of the boat, several folds. Fuel cell-based AIP has merits in performance compared to other technologies”.

Importance of the fuel cell-based AIP of NMRL has been explained due to hydrogen generated onboard. This technology has been developed with private sector partners L&T and Thermax and is ready for fitment into target vessels as per the press release.

On March 10 India is expected to commission the INS Karanj the third in the Scorpene class.

Thus a review of the submarine capability of the Indian Navy based on numbers and potential as compared to Pakistan at present and the future is relevant.

India’s Submarine numbers

India’s overall conventionally powered submarine requirements are said to be 24 in number. Presently the Indian Navy is fielding 15 submarines – 8 Sindhughosh or Kilo class, 4 Shishumar or HDW class and 3 Kalvari or Scorpene class. Of these the Sindhughosh and Shishumar class are either undergoing or will undergo refit.

In addition there are three nuclear powered submarines – the Chakra leased from Russia and two from the Arihant class which are ballistic missile subs.

India plans to field six SSBN and six SSK or hunter killer nuclear powered submarines in the future.

India’s Conventional Submarine Potential

The main determinants of submarine potential would be weight of carriage, stealth and duration of submergence.

The Sindhughosh class has a displacement of 3000 tons and operational period of 45 days.

The Kalvari class has a displacement of 2000 tons and operational period of about 50 days

The Sishukumar class has a displacement of 1850 tons and operational range of 13,000 to 15,000 kms with an operational period of 50 days.

The Sindhughosh and Sishukumar submarines are of the 1990’s vintage and thus their submerged capability is considered to be limited. This would require the submarines to surface frequently for recharging the batteries by running diesel motors which may render them vulnerable to detection.

Potential Enhancement with AIP

H I Sutton, noted analyst of naval and submarine capability development who publishes on the popular blog Covert Shores has indicated that Kalvari class will be upgraded with the DRDO designed AIP starting in 2023-24 by lengthening the Hull. This will extend endurance by two weeks thereby enhancing potential.

However, Sutton notes that Pakistan has three Agosta Class submarines with AIP which have the MESMA (Module d'Energie Sous-Marine Autonome) system which burns ethanol with oxygen as opposed to hydrogen used by the fuel cells. MESMA technology is not likely to be pursued future in AIP design.

Pakistan has also ordered 8 Type 093 B Yuan Class Submarines from China which has an alternative AIP called a Stirling generator, which uses a closed-cycle diesel engine as per Hutton.

The 093 B has 3600 ton weight and four will be delivered to Pakistan by 2023 to 2028 about the same time that the Indian Navy will upgrade the Scorpene class.

Capability Review

Pakistan presently fields five submarines - three of which have AIP and hence longer endurance. On the other hand it is set to induct 8 submarines in the coming years with AIP from, China thus AIP based potential is set to increase to 11 by the end of the decade.

India on the other hand will be fielding six Scorpene class submarines with AIP modification by end of the decade.

India would have an advantage in terms of nuclear powered submarines likely to field at least 4 to 6 by end of the decade but in terms of AIP based conventional submarines in terms of numbers catchup with Pakistan will be necessary by accelerating the 75 I programme.


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