The Indian Navy’s Kalvari class submarines will get the Made-In-India Air Independent Propulsion (AIP) only when INS Kalvari, the lead submarine, goes to a refit in 2024, according to a report.

Earlier in January 2023, the Ministry of Defence (MoD) issued a statement stating that DRDO’s Naval Material Research Laboratory (NMRL) and France’s Naval Group had signed an agreement for the integration of the NMRL-designed AIP system on INS Kalvari.

INS Kalvari was inducted into the Indian Navy in 2017. The submarine, the lead boat of the Scorpene-class, was built under a deal worth $3.5 billion with the French Naval Group.

The deal also included the integration of the NMRL-designed AIP in the last two submarines. However, the integration was delayed due to a delay in the development of the AIP.

The report reveals that the integration of the AIP will be done when INS Kalvari goes for a refit in 2024.

The process of integration will involve cutting the submarine hull in half, after which the hull will be welded back with the AIP sections in between.

This process will make the submarine longer and heavier and will require further testing.

Defence Research and Development Organisation (DRDO)’s industrial partner Larsen & Toubro (L&T) and Thermax will manufacture the AIP while the French Naval Group will be the lead integrator, the report says.

Air Independent Propulsion

An AIP system gives a submarine the ability to remain submerged underwater, away from enemy sensors, for a long time without surfacing.

A diesel-electric submarine, not equipped with an AIP, has to snorkel frequently to recharge its batteries which power its propellers and other equipment.

The process of snorkelling involves travelling just below the surface of the water, with the submarine’s periscope and generator exhaust pipe above the surface.

An AIP system reduces the need for snorkelling by enabling it to generate electricity for charging its batteries, while completely submerged.

The DRDO’s lab NMRL successfully conducted trials of the land-based prototype of the AIP system in March 2021.

The Print’s report further says that the system has shown an endurance of 14 days on endurance mode and two days for max power mode.