A Model of DRDO's Air Independent Propulsion (AIP) on display at DefExpo 2020

The DRDO has been working with the Navy to develop it at the Naval Materials Research Laboratory (NMRL) in Pune.

In a major boost to Prime Minister Narendra Modi's Make in India programme, the Indian Navy would fit their Kalvari-class submarines with DRDO-built Air Independent Propulsion (AIP) systems, which would allow the underwater warships to remain below the surface for longer periods while carrying out their operations.

An AIP is fitted on the conventional diesel-electric submarines and significantly enhances the capability of the boats to stay underwater, which, otherwise, have to come to the surface to charge their batteries frequently. "The DRDO-built AIP would be fitted on the Kalvari class submarines during their refit programme. The first refit of the first boat INS Kalvari is scheduled for the year 2023," French firm Naval Group's Senior Executive Vice President Alain Guillou told ANI. The French industry official was in India for the biennial DefExpo in Lucknow.

He said the DRDO AIP has been found good and compliant and would add to the capabilities of the submarines.

The DRDO has been working with the Navy to develop it at the Naval Materials Research Laboratory (NMRL) in Pune.

The Indian AIP was earlier supposed to be fitted only on the fifth and the sixth boat but it has now been decided that it would be equipped on all the six boats as and when they go for their major refit programs.

The first boat was inducted by the Navy a couple of years ago and the last boat is expected to be commissioned with full firepower by the end of 2022.

Indian public sector firm Mazagon Dockyards Limited and the Naval Group are building the submarines together in Mumbai.

Guillou said his firm was also taking part in the Indian Navy programme for supplying torpedoes for the Kalvari class boats and was offering its F-21 torpedo for the project.

The heavyweight torpedoes are also supposed to be used by the Indian Navy for its strategic nuclear submarines as they are also functional without their main underwater weapons.