In a major transformative breakthrough for the Indian Navy, the Kalvari-class submarines developed under Project-75 will soon be equipped with the Air Independent Propulsion (AIP) system, a technology that helps conventional submarines to lurk under the surface of water for a longer time.
The steel cutting ceremony for the Defense Research and Development Organisation (DRDO)-developed Air Independent Propulsion (AIP) system took place on December 28.
The ceremony was presided over by Samir V. Kamat, the Secretary of the Department of Defense Research and Development (DDR&D) and the Chairman of DRDO. The steel-cutting reportedly took place at the Larsen & Toubro (L&T) Hazira facility.
DRDO and L&T signed a contract to supply two Air Independent Propulsion (AIP) System Modules for the Indian Navy’s Kalvari Class submarines in June 2023.
At the time, L&T said in a statement: “These Modules constitute the core of the fuel cell-based AIP System, indigenously developed by Naval Materials Research Laboratory (NMRL) of DRDO with L&T as a prime industry partner, an association spanning more than a decade.”
Notably, the steel-cutting ceremony comes months after Kamat inaugurated an AIP Integration and Testing facility at AM Naik Heavy Engineering Complex on July 6, 2024.
The advanced system is expected to be built and tested at this complex by the end of 2025, following which it will be fitted onboard the submarine at Mazagaon Dockyard Limited (MDL). This indigenously developed fuel-cell AIP will be fitted onboard the INS Kalvari submarine when it undergoes its first major refit in September 2025.
INS Kalvari is the first of the six Scorpene class submarines designed by the French Naval Group and produced indigenously at Mazagaon Dockyard Limited under Project-75.
According to reports, adding an AIP onto an operational submarine would require cutting the submarine into two halves. Once cut, an AIP would be installed, increasing its length and weight.
Naval Group will likely oversee the complex procedure, and the technology will be put through additional testing before being installed in the remaining Scorpene-class submarines. In a nutshell, INS Kalvari would function as a testbed for the indigenously developed AIP ahead of its widespread integration into the submarine force.
Since these repairs and refitting will take place over a year, some experts have warned that upgrading the platform with new technology will reduce the operational readiness of the Navy. However, the integration of the indigenously produced AIP into an Indian submarine has also been hailed as a monumental breakthrough for the Indian Navy’s capabilities.
Why Is Indigenous AIP A Gamechanger?
Air-independent propulsion (AIP) is any maritime propulsion technology that enables a non-nuclear submarine to function without requiring oxygen from the atmosphere. AIP decreases the submarine’s vulnerability to detection by increasing its underwater endurance between battery charges by three to four times.
AIP-powered conventional diesel-electric submarines (SSK) are midway between nuclear-powered submarines and non-AIP diesel-electric submarines. They let an SSK stay underwater for 10 to 14 days without snorkeling to the surface to recharge its batteries, which leaves the submarine vulnerable. Additionally, the fuel-cell-based AIP is unique, as it generates its hydrogen requirement on board.
The AIP-enabled submarines have increased mobility. They can “bottom” or sit on the ocean floor with only critical systems running to preserve energy and extend the operational time while using passive sonar to detect targets.
Since fuel cells operate with greater efficiency at lower loads, bottoming could extend the endurance of a particular mission. The Kalvari-class submarines will be upgraded with the AIP Plug, incorporating these AIP modules. The Energy Modules (EMs) can generate hydrogen on board and provide the necessary power.
With an enhanced maritime threat from adversaries like China and Pakistan, the Indian submarine fleet will benefit immensely from the AIP technology. For one, these submarines would be able to effectively monitor the growing Chinese naval presence in the Indian Ocean without being detected.
Unlike India, both China and Pakistan have AIP technology, putting India at a competitive disadvantage. Pakistan has deployed AIP-equipped French Agosta-90B submarines for a long time and is currently working with China to construct Hangor-class submarines, which also have AIPs.
Against that backdrop, integrating AIP into its SSK fleet will be a game-changer for the Indian Navy, particularly given the growing number of Chinese and Pakistani ships straddling the Indian Ocean Region (IOR).
In fact, the AIP technology is so crucial that it has become the bedrock of India’s submarine acquisition under Project-75I, which continues to hang in the balance due to unforgiving, stringent requirements.
India To Boost Its Combat-Prowess With Project-75I
The Indian Navy has been looking for six submarines under its Project-75I. These submarines will have Fuel Cell Air-Independent Propulsion (AIP) technology, allowing them to stay hidden in the ocean’s depths for extended periods and, if necessary, rush to their target at great speeds without revealing their position.
Currently, the project has two frontrunners: the state-run MDL with its foreign partner TKMS and the Indian private manufacturer L&T in collaboration with Navantia.
The TKMS has pitched its Type 214 submarine tailored to India’s specific requirements, and Navantia has offered the S-80. Both contenders have offered the AIP to India.
Of these, Navantia’s AIP Bioethanol Stealth Technology (BEST) system uses hydrogen generated onboard from a fuel, in this case bioethanol, rather than pure stored hydrogen. Navantia claims that this gives the submarine a tactical and safety advantage and increases the strategic autonomy and deterrence capability. By using this technology, the submarine can carry more energy and stay underwater for up to three weeks.
On the other hand, the German AIP has a Lithium-Ion battery. Since it offers long-range endurance and enables the submarine to cruise at high speed to reach its target, the TKMS has positioned it as a game changer. It states that combining a fuel-cell-based AIP system and a Lithium-Ion battery will bring a game-changing capability to the Indian Navy.
Indian Navy finished evaluating submarines offered by the German Thyssenkrupp and Spanish Navantia earlier this year. However, if reports in the Indian media are anything to go by, none of the AIPs tested by the Indian Navy have fully satisfied its requirements.
The Spanish AIP had not been installed into the S-80 during field testing by the Indian Navy, and the German AIP, although operationally tested, was found to be smaller.
On its part, the Indian Navy is yet to decide on the winner of the Project-75I bidding. However, it is safe to say that among a host of requirements mentioned in the Indian Navy’s Request for Proposal (RFP), the AIP may be one of the most critical and one India cannot compromise with.
For now, one thing is clear: if India wants to compete effectively against Pakistan and China, it must level up its underwater game. The Indian Navy is not looking to maintain a competitive edge by being the biggest and fastest but rather by being the quietest and most lethal, for which the AIP technology is indispensable.
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