Why in News?

• The third Scorpene class submarine ”Karanj” is about to be delivered to the Indian Navy by the end of 2020.
• INS Karanj is a part of Project-75 which is currently in advanced stages of sea trials.

About Project-75:

• It is a programme by the Indian Navy that entails building six Scorpene-Class attack submarines.
• The programme has been undertaken with transfer of technology from French company Naval Group (formerly known as DCNS) at the Mazagon Dock Limited (MDL).

About Scorpene Submarines:

• The submarines in the Project-75 Scorpene-Class are powered by the conventional diesel-electric propulsion system.
• The first Scorpene submarine, Kalvari, was commissioned in 2017. It is supposed to go for a normal refit after six years in 2023, during which time the Air-Independent Propulsion (AIP) would be installed in it.
• Second Scorpene “Khanderi” was inducted in September 2019.
• The remaining submarines (Vela, Vagir, and Vagsheer) in the series are in advanced stages of manufacturing and trials.
• List of Six Scorpene class Submarines:

1. Kalvari

2. Khanderi

3. Karanj

4. Vela

5. Vagir

6. Vagsheer

About “Air-Independent Propulsion System”:

• Conventional submarines use a diesel-electric engine, and must surface for oxygen required for fuel combustion. If fitted with an Air Independent Propulsion (AIP) system, the submarine needs to take in oxygen less frequently.
• Diesel-electric submarines require them to come to the surface frequently to charge their batteries, since their underwater endurance time is less. ‘Air-independent’ propulsion technology helps to make the diesel generator less dependent on surface air.
• AIP technology is being developed by the Defence Research and Development Organisation (DRDO) to provide submarines long-range and extended endurance capabilities undersea.
• Significance:
• 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.