Diesel-Electric Submarines P75-I

The Scorpene-class Diesel-Electric Submarines P75-I / air-independent propulsion (AIP) submarines are based on the Scorpene-class submarines, which were designed by a French naval shipbuilding firm DCNS in partnership with Spanish shipbuilding firm Navantia.

The Indian Navy’s Project 75I (P75I) Scorpene submarine development for six latest-generation attack boats is expected to be completed by 2022.

About Project 75-I project

  • This Project is part of India’s 30-year submarine construction plan that ends in 2030. 
  • Six Scorpene-class submarines are being built under Project-75 by Mazagon Dock Limited (MDL), Mumbai, under technology transfer from the Naval Group of France. It is apart of a $3.75 billion deal signed in October of 2005.

Six Submarines Under Project 75-I

NameDate of LaunchDate of Commission
Kalvari27 Oct 201514 Dec 2017
Khanderi12 Jan 201728 Sep 2019
Karanj31 Jan 201810 Mar 2021
Vela06 May 2019 —
Vagir12 Nov 2020 —
Vagsheer —

Comparison with other Naval forces

  • The naval force of Pakistan is estimated to have ten submarines, of which five French-origin Agosta 90B class (Khalid class) conventional vessels are fully operational.
  • Pakistan Government has signed a deal for eight conventional submarines with China after it failed to get the vessels from France and Germany due to price and technology transfer issues.
  • According to some media reports, China’s People’s Liberation Army Navy (PLAN) has four Jin-class SSBNs and nine SSNs.
  • Some reports also suggest China has a fleet of 40-plus diesel-electric submarines beset by maintenance issues.
  • This Submarine project will not only be a significant increase in the Indian Navy’s firepower but also ensure the stronghold of India in the Indian Ocean region.

Diesel-electric Submarines

  • When the submarine operates underwater, the batteries onboard power the propeller and other electrical systems onboard the submarine. 
  • The batteries run out of charge within 4-5 days, and the sub needs to recharge them. This is done by snorkelling, which exposes them to detection by enemy radars and makes them an easy target for hostile anti-submarine assets.
  • Although modern snorkels are coated with radar-absorbing paint and stealthy, they are still detectable by high-resolution radars.
  • There are also sensors called diesel sniffers, which can easily detect the exhaust emissions of the submarines diesel generators while snorkelling.
  • A submarine that needs to surface every day loses its ability of surprise and increases its vulnerability to hostile anti-submarine assets.
  • AIP systems allow conventional submarines to recharge their batteries without surfacing for air, which enables them to remain underwater for extend periods and not expose themselves to detection. 
  • AIP is a technology based on the combustion of stored oxygen and ethanol to increase the battery-powered propulsion system.
Diesel-Electric Submarines P75-I

Significance of AIP:

  • Air-Independent Propulsion significantly improves the stealth of the Submarine because it enables a sub to generate electricity for services, battery charging, and propulsion while completely submerged underwater.
  • AIP systems also generate electricity, powering a submarine also generate oxygen, lighting, and amenities for the crew.


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