Explained: What's Holding Up Indian Navy's Project To Get Submarines That Can Stay Underwater Longer

The Indian Navy's project to acquire conventionally powered submarines capable of staying underwater longer has been mired in delays for years.

And, unsurprisingly, it’s facing yet another setback.

Project 75 India (P-75I) was first envisioned in 1998 as part of a 30-year submarine-building plan, set to conclude in 2030. Under P-75I, the Navy plans to acquire six new conventional diesel-electric submarines equipped with air independent propulsion (AIP) technology.

After years of uncertainty, two main contenders have emerged to meet the Navy’s needs. One is the German submarine manufacturer ThyssenKrupp Marine Systems (TKMS), which has partnered with the state-owned Mazagon Dock Shipbuilders Limited (MDL) to bid on the project. The other is Spain’s Navantia, which has teamed up with private Indian company Larsen & Toubro (L&T).

Before diving into the current holdup, it’s crucial to understand the significance of AIP technology.

AIP systems allow submarines to remain submerged for extended periods, reducing the need to surface and risk detection by enemy sensors. Traditional diesel-electric submarines without AIP must snorkel regularly to recharge their batteries, which power the vessel’s propellers and other systems.

Snorkelling involves moving near the surface with the submarine’s periscope and generator exhaust pipe exposed above water.

This process can increase the risk of detection, as modern radars, like the Telephonics AN/APS-153(V) on the Indian Navy’s MH-60R helicopters, can easily spot the periscope and exhaust pipes. This is a significant vulnerability in hostile waters.

In contrast, AIP allows a submarine to recharge its batteries while remaining fully submerged, minimising exposure and enhancing stealth.

Currently, the Indian Navy operates no AIP-equipped submarines, whereas Pakistan has been using French-made submarines with AIP for years and is in the process of building eight more with Chinese assistance.

Now that we've looked at AIP technology, the next question is: what’s causing the delays in P-75I?

The issue lies in the Navy’s requirements.

The request for proposal (RFP) mandates that the supplier must offer a submarine with a sea-proven AIP system. Unfortunately, neither TKMS nor Navantia meets this criterion.

Navantia’s AIP system, while closest to the Navy’s specifications, will not be operational on its submarines until 2026 — something Indian authorities were aware of from the start.

Navantia demonstrated its AIP during the trials using a combination of land and onboard systems, but it is up to the Navy to decide if this qualifies as "proven" technology.

The system has already undergone more than 50,000 hours of testing and has been selected for installation in the Spanish Navy's S-80 class submarines.

Navantia’s AIP has been approved by the Spanish Navy and will be fitted onto its third S-80 class submarine, reinforcing the system’s technological readiness.

Meanwhile, TKMS’ AIP, originally designed for its smaller Type 214 submarines, falls short of the size requirements for the Indian Navy. The Germans would need to develop a larger AIP system to meet the specifications.

Another issue with TKMS’ bid is the need to develop a new submarine design for the Indian Navy, whereas Navantia is offering its already operational S-80 class submarines, which were inducted into the Spanish Navy in 2023.

TKMS would also need to test new fuel cell batteries, as those used in their submarines are produced by a different manufacturer than the ones offered for India.

The Navy’s insistence on a proven AIP system is partly driven by concerns that India’s Defence Research and Development Organisation (DRDO) might claim its indigenously developed AIP system could fulfil the requirement, which would only result in further delays.

India has been building Scorpene-class submarines, with plans to integrate an indigenous AIP system into the fifth and sixth vessels. However, both have missed deadlines. The current plan is to retrofit the first Scorpene-class submarine undergoing refit next year with an AIP system, though even this remains uncertain due to ongoing trials.

The challenges plaguing P-75I today were anticipated years ago. Russia, once considered a contender for the project, warned that without "drastic changes" to the Indian Navy’s tender, the program would face significant hurdles.

Russia noted that no other naval force in the world operates submarines like the ones India is seeking, meaning the vessels would need to be designed from scratch.

Sweden’s SAAB was the first to withdraw from the race in 2019, even before a formal tender was issued, citing “unbalanced” strategic partnership requirements.

Nearly five years later, P-75I remains stuck in limbo, with no signs of moving to the next phase anytime soon.