AIP gap adds to India's submarine challenge

Even though the Defence Research and Development Organisation (DRDO) is developing an AIP system, which will be deployed in Kalvari-class submarine, sea trials will take another year for it to be finalised for mass production.

According to the Indian Navy’s long-term submarine modernisation plan, approved by the Cabinet Committee on Security in 1999, India was expected to build 24 conventional submarines by 2030 through phased construction.

The submarines were to be inducted in batches of six, with Scorpene-class boats under Project 75 (P-75), followed by six advanced AIP-equipped submarines under Project 75 India (P-75I). The plan was later revised, replacing six of the proposed 12 indigenous conventional submarines under Project 76 with six indigenous nuclear-powered attack submarines (SSNs) under Project 77.

However, this programme faced repeated delays due to procurement procedures, technology transfer negotiations, industrial bottlenecks and funding constraints. While all six Kalvari-class submarines under P-75 have now been inducted, P-75I is still facing procurement delays.

Experts say the delays are affecting the navy’s ability to maintain sustained underwater presence in the region amid a growing maritime challenge from both Pakistan and China.

While India is working towards integrating the technology into its fleet, Pakistan is the only country in South Asia currently operating AIP-equipped conventional submarines. 

“It is not a doctrinal gap. The doctrine exists and caters for underwater warfare. The real issue is a capability gap in numbers. India simply does not have enough submarines to maintain credible underwater presence,” said Sarabjeet Singh Parmar, retired Indian Navy Captain and distinguished fellow at New Delhi-based think tank, United Service Institution of India.

Parmar said submarines operate on rotational deployment cycles, which means not every submarine is always available for missions. “Navies across the world follow the ‘one in three’ or ‘one in four’ rule. To keep one submarine operationally deployed at sea at all times, you effectively need three or four submarines because one is deployed, one is recovering and training, and another is in refit,” he added.

Speaking about India’s lack of AIP-equipped submarines, Commodore Abhay Singh (retired), currently associated with Manohar Parrikar Institute for Defence Studies and Analyses, said the debate around AIP sometimes overshadows the larger structural issue.“India’s real problem is not the absence of AIP-equipped submarines alone. The larger concern is the dwindling number of submarines in the fleet. At this stage, India first needs submarines in adequate numbers,” Singh said. He added that India deliberately chose the more difficult path of developing indigenous technology instead of depending entirely on imported systems, which increased timelines, but at the same time gave India greater long-term control over the technology.

Parmar said the operational advantage of a submarine equipped with AIP is stealth. The longer a submarine remains submerged, the lower the probability of detection.“Movement underwater is slow because speed creates noise and noise increases detectability,” Parmar said.

The discussion around India’s underwater gap has gained attention following Pakistan’s induction of the Chinese-built Hangor-class submarine — PNS Hangor — in April in China. It was seen in Malaysia enroute to its base. It is based on China’s Type-039B Yuan-class submarines and is equipped with AIP systems and advanced technology, increasing its stealth patrol capability.

While the induction has drawn attention in the region, experts cautioned that the operational effectiveness of these platforms is yet to be fully proven. “Pakistan’s Chinese-origin AIP submarines may appear impressive in brochures, but their real operational effectiveness remains largely untested and unproven,” Singh noted.He cautioned that many submarine technologies advertised globally do not always deliver to their full claimed capability in actual operational conditions.

At the same time, Parmar explained that Pakistan’s submarine expansion is part of a broader asymmetric naval strategy aimed at competing with India’s larger conventional maritime strength. “Pakistan is attempting to offset India’s conventional naval superiority through asymmetric means, and submarines are central to that strategy,” he said.

The challenge not only lies with Pakistan but also with China, as the latter is expanding its naval presence in the Indian Ocean Region. China operates a total of 59 submarines, including SSBNs, SSNs and conventional diesel-electric attack submarines, according to “The Military Balance 2025” report by the UK-based International Institute for Strategic Studies. The report notes that less than half of China’s conventional diesel-electric attack submarines are equipped with AIP technology. 

Experts said that India’s challenge today is not limited to submarine numbers alone but in future underwater warfare as well, including unmanned underwater vehicles, autonomous systems and advanced anti-submarine warfare technologies. “Hundreds of unmanned underwater vehicles operating simultaneously could completely complicate underwater detection and anti-submarine warfare,” Parmar added.

As India is simultaneously working on indigenous SSN development and future submarine projects beyond P-75I, the broader issue extends beyond technology itself. The navy has also pushed for faster submarine production cycles to avoid capability gaps caused by retiring platforms.

Parmar also pointed to technology transfer as a major hurdle in India’s submarine modernisation efforts. “The issue is not merely procurement as foreign vendors are often reluctant to transfer critical technologies because doing so eventually creates competition for themselves,” he added.

Singh, meanwhile, said the delays stem from a combination of financial, procedural and industrial challenges. “The delay in submarine induction is a combination of constrained budgets, lengthy acquisition cycles, indigenous development challenges, production bottlenecks and shifting strategic priorities,” he noted.

Immediate crises or tense situations have often put long naval projects on standstill. “Naval platforms have very long gestation periods. Whenever immediate crises emerge, whether Kargil or Galwan, long-term capability development tends to get pushed temporarily to the back burner,” Singh added.

Experts note that despite delays, the Indian Navy remains one of the country’s most indigenous services in terms of shipbuilding capability. As India already designs and builds a large share of its surface warships, the challenging areas like propulsion technologies, underwater endurance systems and advanced submarine ecosystems still require investment and long-term industrial support. 

Therefore, the AIP debate is no longer only about one technology but a wider question involving submarine numbers, industrial capacity, underwater stealth and the pace at which the country can respond to an evolving maritime threat by adversaries.