India has joined a select group of countries to have an Air Independent Propulsion System (AIP) that permits conventional submarines to remain under water for longer.

The Defence Research and Development Oragnisation (DRDO) achieved the important milestone by successfully completing the trial of the land-based prototype on 8 March.

“The plant was operated in endurance mode and max power mode as per the user requirements,” the DRDO said in a statement Tuesday.

Sources in the defence and security establishment said that the endurance mode was for 14 days and max power mode was for two days.

“These were the requirements as sought by the Navy. It has been fulfilled and one can now say that India has AIP technology,” a source said.

As per a report of 30 December, the AIP trial was among the major ones planned by DRDO for 2021.

Apart from India, the countries to have AIP technology are China, Germany, Sweden, France, Spain and Russia. The US has not concentrated on AIP since they operate nuclear submarines.

India’s next set of conventional submarines, under Project 75 India, will have AIP technology. The project is being pursued under the Strategic Partnership model and the two Indian shipyards selected by the Navy for the eventual contract are state-owned Mazagon Dockyards Limited and private firm L&T.

The Navy will select a foreign firm to partner with one of these Indian companies. The formal Request for Proposal (RFP) is yet to be issued for the project.

Meanwhile, sources said that the Scorpene submarines, being built in collaboration with France, will also have the AIP technology fitted on them during their scheduled major refit.

AIP has a force multiplier effect on the lethality of diesel-electric submarines as it enhances the submerged endurance of the boat.

The DRDO said that fuel cell-based AIP has merits in performance compared to other technologies.

The system has been developed by Naval Materials Research Laboratory (NMRL) of DRDO with the support of industry partners L&T and Thermax.

“While there are different types of AIP systems being pursued internationally, fuel cell-based AIP of NMRL is unique as the hydrogen is generated onboard … It has now reached the stage of maturity for fitment into target vessels,” the DRDO statement said.