India tests indigenous AIP system for Kalvari submarines


India’s Defence Research and Development Organisation (DRDO) has successfully tested an indigenously developed fuel-cell based air-independent propulsion (AIP) system intended to be retrofitted to the Indian Navy’s six licence-built Kalvari (Scorpène)-class diesel-electric submarines (SSKs).

The government’s Press Information Bureau (PIB) announced on 9 March that the successful developmental trials of the land-based AIP prototype, which was developed by DRDO’s Naval Materials Research Laboratory (NMRL) at Ambernath in partnership with Larsen & Toubro, Thermax, and the Centre for Development of Advanced Computing, indicate that the system has “reached the stage of maturity for fitment into target vessels”.

According to the MoD, the land-based prototype “was operated in endurance mode and max power mode as per the user requirements” in a test that had been completed in Mumbai on 8 March.

While the PIB statement did not provide further details on the AIP prototype, it is understood that the DRDO has been working on phosphoric acid fuel cell (PAFC) technology for several years. The agency had earlier focussed its efforts on the design and engineering of the PAFC and its liquid oxygen system with aid from Naval Group, the original designer of the Scorpène SSK.

The AIP retrofit will require the hulls of the Kalvari SSKs to be cut open to insert an additional 10 m section. Retrofit work is likely to be undertaken by Mazagon Dock Shipbuilders (MDL) during the boats’ scheduled mid-life upgrade programme.

The DRDO announcement came a day before INS Karanj, the third Kalvari-class SSK, was commissioned into service in Mumbai. The fourth and fifth submarines of the class, Vela and Vagir, were launched in May 2019 and November 2020 and are expected to enter service around 2022.

The sixth and final submarine on order, Vagsheer, is being constructed by MDL and is expected to be launched within 2021.

Kalveri-class SSKs displace 1,775 tonnes when submerged and features advanced quieting systems designed to increase stealth. If successfully completed, the AIP retrofit to these boats would significantly enhance their underwater endurance.

by Jr Ng