Indian Navy’s third stealth Scorpene-class Submarine INS Karanj has been commissioned into the Indian Navy. It also completed the trials of the Indigenous Air Independent Propulsion (AIP) System jointly developed by Naval Materials Research Laboratory (NMRL) and DRDO.

In a rare case, we would see a question based on various classes of Indian Submarines in the CSP. However, we can expect a question based on the AIP system in the CSP and CAPF exam.

INS Karanj

• INS Karanj is the third submarine of the first batch of six Kalvari-class submarines for the Indian Navy.
• It is a diesel-electric attack submarine based on the Scorpene-class, designed by French naval defence and energy group DCNS and manufactured by Mazagon Dock Limited, an Indian shipyard in Mumbai.

What is AIP?

For this, we have to understand how a submarine works. Traditionally we hear about two types of submarines- Nuclear and Diesel Electric.

Diesel Electric Submarines

• While Nuclear Submarines can stay submerged for a prolonged period and remain undetected, Diesel Electric submarines cannot do so, and they must surface after a stipulated time interval.
• Their Diesel Propulsion would need air to run the engine like any other Vehicle or Aircraft engines and for this, they would need oxygen which is not available underwater.
• Hence they have to move closer to the surface so that their engines can breathe air through their snorkels.

So, these diesel turbines charge the batteries available in the submarine and once the batteries are fully charged, the submarine goes underwater where the propeller shaft, as well as other systems, runs on the power stored in the batteries.

• This makes the Submarine very much vulnerable to threats from Air, Sea or even underwater.
• Not only has this, but the storage of excessive fuel also reduced the overall performance and weapon holding of the submarine too.

Why don’t we can induct only the Nuclear Submarines in the Navy?

• Though nuclear submarines can stay underwater for months, they cannot do so with total stealth.
• While a diesel-electric submarine (while underwater) is making no noise, Nuclear submarines have a lot of vibrations that are generated from the coolant pumping system of their reactors which must run nonstop.
• This makes even nuclear submarines vulnerable to depth sonars.
• Moreover, the manufacturing cost of these submarines is several times higher than those of diesel-electric ones.
• So, the most effective and commercially viable solution is a diesel-electric submarine with AIP.

What is AIP, then?

• Over the years the biggest challenge before the mariners was to ensure that the submarines can sustain underwater for a prolonged time.
• AIP is any marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen (by surfacing or using a snorkel).
• While there are different types of AIP systems being pursued internationally, the DRDO has applied fuel cell-based AIP using hydrogen onboard.
• Fuel cell-based AIP has merits in performance compared to other technologies
• While the first two submarines (INS Kalvari & INS Khanderi) are equipped with French-made AIPs, the rest of the submarines will be equipped with an Indian system.

Note: The Project 75I-class submarine is a follow-on of the Project 75 Kalvari-class submarine for the Indian Navy.

Significance for India

• With this induction, India has joined the club of six other elites who have the capacity to design and install such complex systems.
• These countries are France, China, Spain, Sweden, Germany and Russia.
• Indian AIP system is unique. It is one of the most advanced AIP systems of the world where Fuel Cell technology is used to generate onboard power.
• With indigenous AIP, submarines can stay underwater for more than 3 weeks in low consumption mode, more than 2 weeks in endurance mode and 2-4 days in max power mode.

Back2Basics: Various classes of Submarines in India

In maritime terms, a class of ships is a group of vessels that have the same make, purpose and displacement.

• Chakra Class: Under a 10-year lease from Russia since 2012
• Arihant Class: Nuclear-powered ballistic missile submarines
• Shishumar Class: Diesel-electric attack submarines Indian variant of the Type 209 submarines developed by the German Navy
• Kalvari Class: Diesel-electric attack submarines designed by French company DCNS
• Sindhughosh Class: Kilo-class diesel-electric submarines built with the help of Russia

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