An Scorpene-class submarine of the Indian Navy. The Defence Research and Development Organization (DRDO) successfully conducted the final test of the land-based prototype of the Air Independent Propulsion (AIP) system in Mumbai on Monday (9 March). The AIP system will be retrofitted into the Kalvari class submarines, whose third model INS Karanj is set to be commissioned on Wednesday. This new AIP system means the diesel submarines can stay underwater for longer periods of time and become more silent than nuclear submarines. This latest development is seen as Indiaâs conscious efforts to build capabilities and counter the emergence of the Chinese naval force.