The third indigenously-built Scorpene class submarine INS Karanj

"The Defence Research and Development Organisation is pushing for the inclusion of their under-development AIP on the P-75 India but it has not yet been included in the tender," sources told ANI.

The Indian Navy would soon come out with the tender for over Rs 50,000 crore project to build six indigenous conventional submarines but they would not be fitted with the indigenous Air Independent Propulsion system that is being developed by the DRDO.

The air-independent propulsion (AIP) technology enhances the underwater endurance and stealth of conventional submarines who otherwise have to come on the surface to use oxygen to recharge their batteries.

The Defence Acquisition Council headed by Rajnath Singh recently cleared around Rs 50,000 crore project codenamed P-75 India for the Indian Navy to move ahead with the construction of six new conventional diesel-electric submarines within the country.

"The Defence Research and Development Organisation is pushing for the inclusion of their under-development AIP on the P-75 India but it has not yet been included in the tender," sources told ANI.

As per sources, the Indian Navy has asked the DRDO to prove the AIP on a platform before it is allowed to be put on the Scorpene-class submarines when they start coming for their scheduled refits, they said.

It is learnt that the Navy would allow the contenders for its project to use the currently operational AIP systems which would be available with foreign original equipment manufacturers (OEMs) only.

The project is expected to take at least two years before the Navy is able to find out the winner for the programme which would include Larsen and Toubro along with the Mazagon Dockyards Limited as the strategic partners and five foreign firms as the original equipment manufacturers who would partner with these two to offer their systems in the competition.

The DRDO in March this year had stated that it has achieved an important milestone" in the development of the indigenous AIP system by proving its land-based prototype.

Developed by the Naval Materials Research Laboratory (NMRL) of DRDO with the support of industry partners L&T and Thermax, the AIP system was operated in endurance mode for 14 days and maximum power mode for two days.

The 270 Kilowatt fuel cell-based AIP system will begin to be fitted on the Scorpene submarines.