Air Independent Power (AIP) greatly increases the survivability of non-nuclear submarines by increasing their underwater endurance. The Indian Navy, unlike its potential adversaries of China and Pakistan has not yet fielded AIP on any its submarines however.
This is changing as India’s indigenous effort to develop this technology moves closer to fruition. According to Naval News, India’s Defence Research and Development Organisation (DRDO)’s land-based test plant has reached an important milestone. It has been “operated in endurance mode and max power mode as per the user requirements.”
Work has been underway for several years at DRDO’s own Naval Materials Research Laboratory (NMRL). Engineering firm Larsen & Toubro is also involved.
The system should soon be ready for installation aboard Indian Navy submarines. The current Kalvari class boats are expected to receive it during a major upgrade. This should happen six to seven years after commissioning, so starting in 2023-24.
The refit will include lengthening the hull to fit in the new module. This is a similar approach to how Sweden added AIP to its submarines. The locally designed system is expected to extend the endurance of the submarines by two weeks. This will greatly increase the potency of these non-nuclear submarines.
India will operate 6 Kalvari class attack submarines, which are the newest non-nuclear submarines in the Indian fleet. They are a version of the French-designed Scorpène type submarines. In the French lineage these are a generation newer than the Agosta Class boats in service with neighboring Pakistan.
However three of Pakistan’s Agostas class, the -90B models, already have AIP. For the moment this may confer some advantages to them. Unlike the Indian subs, which will use fuel cells, the Pakistan Navy submarines use the MESMA (Module d’Energie Sous-Marine Autonome) system. This burns ethanol with stored oxygen to produce steam. This is used to turn a turbine, similar to how a nuclear power plant works.
The Pakistan Navy is also buying 8 Type 093B ‘Yuan Class’ submarines from China. These will be known as the Hangor Class locally. They will come with an alternative type of AIP called a Stirling generator, which uses a closed-cycle diesel engine. In general MESMA is unlikely to be fitted to future submarines but fuel cells and Stirling generators are.
India is also developing nuclear submarines, siomething with Pakistan is not expected to do. But AIP equipped non-nuclear boats will remain relevant and in some arenas have an advantage. Having indigenous fuel-cell AIP technology could move India closer to self-sufficiency is submarine design. The next generation of non-nuclear submarines for the Indian Navy, the Project 75I class, are expected to have the new AIP.