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Explained: Why are Air Independent Propulsion submarines significant for India?

The DRDO on Wednesday tested a land-based prototype of an Air Independent Propulsion (AIP) submarine.

, Edited by Explained Desk | New Delhi |
Updated: November 2, 2019 8:32:06 am
Chief of Naval Staff Adm Karambir Singh witnessing operation of land-based prototype of DRDO India Air Independent Propulsion system at Naval Materials Research Laboratory in Ambernath, today. Also seen is Secretary, Dept of Defence R&D and Chairman DRDO Dr G. Satheesh Reddy. (Source: Twitter/DRDO)

The DRDO on Wednesday tested a land-based prototype of an Air Independent Propulsion (AIP) submarine. The prototype operation at the Naval Materials Research Laboratory in Ambernath, Maharashtra, is considered to give a boost to the DRDO’s plan to build AIP systems for Indian naval submarines. The land-based prototype was engineered to the form-and-fit of a submarine.

What is the Air Independent Propulsion (AIP) technology used in submarines?

Submarines are essentially of two types: conventional and nuclear. Conventional submarines use a diesel-electric engine, and must surface daily for oxygen for fuel combustion. If fitted with an Air Independent Propulsion (AIP) system, the sub needs to take in oxygen only once a week.

While many naval powers, including India, have acquired nuclear-powered submarines for deep-sea operations, conventional diesel-electric variants are considered useful for coastal defence. The latter are optimised for stealth, and their weapons and sensors provide for effective operations close to the shore.

Because diesel-electric submarines require to come to the surface frequently to charge their batteries, their underwater endurance time is less. ‘Air-independent’ propulsion technology helps to make the diesel generator less dependent on surface air.

In a fuel cell AIP, an electrolytic fuel cell releases energy by combining hydrogen and oxygen, with only water as the waste product. The cells are highly efficient, and do not have moving parts, thus ensuring that the submarine has a low acoustic signature. Older submarines can be adapted to the AIP system by retrofitting.

A fuel cell-based AIP, like the one developed by DRDO, is known to deliver better performance compared to other technologies. According to the Defence Ministry press release, the AIP system enhances the submerged endurance of diesel-electric submarines several times, thus having a multiplier effect on its lethality.

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