NEW DELHI — In a reversal, the Indian Navy has dropped plans to mount homegrown air-independent propulsion (AIP) technology on the last two of its six Scorpene submarines under construction, putting into question the development status of the technology.

Work on the AIP tech, under development by state-owned Defence Research and Development Organization (DRDO), has held back the floating of the Navy's $12 billion tender for Project 75(I), under which six conventional submarines with AIP technology are to be acquired, according to an Indian Navy official. "With doubts now cleared that the AIP technology is not ready, the chances of the tender being floated early are bright," the official said.

"The decision not to install a homegrown AIP system on the Scorpene submarines appears to be a sound one," said Arun Prakash, a former service chief and retired Navy admiral. "This is an arcane technology, which took France and Germany many years to develop and prove, in terms of efficiency as well as safety. Given state-owned Defence Research and Development Organization propensity for exaggeration and hyperbole, they should first prove the system on land-based test beds, then by retrofitting on an old submarine and only then on a new-build boat."

The last two Scorpene submarines, known locally as Kalveri-class subs, are slotted for induction in 2020 and 2022. A second Navy official said that while Indian defense scientists claim the AIP tech will be ready by 2020, the "Indian Navy is not confident for its integration on the last two Scorpene submarines."

According to a DRDO scientist, the organization is to conduct the first-ever trails of land-based AIP technology in December.

"Substantial design changes will be required to fit the homemade AIP on the Scorpene submarines," said Sujeet Aammadar, a retired Indian Navy commodore and defense analyst. "It is better to commission the Kalveri-class submarines as designed. Later when they fall due for long refits, the homemade AIP can be installed."

Shyam Kumar Singh, a retired Indian Navy captain, said: "The exhaustive testing of DRDO-developed AIP is yet to be completed. In case of submarine you can install any equipment once it is fully proven."

​"The 75(I) tender is about 15 years overdue and if not floated soon could lead to yet another force-level crisis for the Indian Navy. The homemade AIP — if one is in existence — should be considered only after it has undergone stringent testing on other test beds. An operational submarine is no place for a development or experimental AIP," Prakash said.

Rubin Design Bureau of Russia, Germany's ThyssenKrupp Marine Systems, Saab of Sweden and DCNS of France are the front-runners for the Project 75(I) tender.

Five domestic shipyards — Mazagon Dock Shipbuilders Limited, Hindustan Shipyard Limited, Garden Reach Shipbuilders and Engineers, Larsen & Toubro, and Reliance Defence and Engineering Limited (formerly Pipavav Defence) — have been recognized as being capable of building the AIP subs. The tender is to be issued only to domestic shipyards, which in turn will tie up with an overseas shipyard to complete the project.

Anil Jai Singh, a retired Indian Navy commodore and defense analyst, said of the homegrown technology's importance here: "The indigenous AIP development will definitely take priority over any foreign original equipment manufacturer doing so in India."

Vivek Raghuvanshi is the India correspondent for Defense News.

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