The submarine technology that India wants

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The submarine technology that India wants

  • Recently, France’s Naval Group, shortlisted Original Equipment Manufacturers (OEM) for the Navy’s P-75 India (P-75I) project to build six conventional submarines within the country, announced it would not bid for the project.
  • The reason provided was that the Request for Proposal (RFP) requires that fuel cell AIP be sea proven, while the French Navy does not use such a propulsion system.
  • AIP refers to Air-Independent Propulsion, a technology for conventional — that is, non-nuclear — submarines.

What is the P-75I project?

  • In June 1999, the Cabinet Committee on Security approved a 30-year plan for the Navy to indigenously build and induct 24 submarines by 2030.
  • In the first phase, two lines of production were to be established — the first, P-75; the second, P-75I. Each line was to produce six submarines.
  • The contract for P-75 was signed in 2005 with the Naval Group, then known as DCNS, in partnership with Mazagon Dock Shipbuilders Ltd (MDL).
  • The first Kalvari Class (Scorpene-Class) submarine under the project was commissioned in December 2017.
  • Another five submarines have been built since; the final one, Vagsheer, was launched last month, and will be commissioned by late 2023.
  • While P-75 deliveries were delayed, P-75I has seen long delays even before it has kicked off.
  • This will be India’s first project under the Strategic Partnership Model — the government will give the contract to an Indian Strategic Partner (SP), which will partner with a foreign OEM to build AIP-powered submarines in the country.
  • MDL and L&T are the two selected SPs; the five selected OEMs are Naval Group (France), ThyssenKrupp Marine Systems (Germany), ROE (Russia), Daewoo Shipbuilding, and Marine Engineering (South Korea), and Navantia (Spain).

Status of the project

  • The final bids, one each by the SP in partnership with an OEM — are yet to be finalized.
  • The project is facing turbulence; the Naval Group has already announced it is pulling out, and sources said the Russian and Spanish companies might also not proceed with their bids.
  • Among the concerns is the requirement to demonstrate a sea-proven fuel cell AIP.
  • While some manufacturers may have the technology, it may not have been proven at sea yet.
  • Some analysts believe that while the RFP was clear about these conditions, it is possible that the OEMs were expecting certain concessions in the requirements eventually.
  • Another problem for the OEMs is the transfer of technology, which is built into the process under the SP model.
  • OEMs are unwilling to share all their expertise, especially the niche technologies that they have built.
  • According to experts, even if all goes smoothly here onward, the earliest the first P-75I submarine can be commissioned is around 2032.

Why does the Navy want AIP subs?

  • Fuel cell-based AIP has merits in performance compared to other technologies.
  • AIP technology allows a conventional submarine to remain submerged for much longer than ordinary diesel-electric submarines.
  • All conventional submarines have to run their generators that recharge the batteries that allow the boat to function under water.
  • However, the more frequently a submarine surfaces, the higher the chances of it being detected.
  • Diesel-electric submarines must come to the surface or close to it to run their generators to recharge the batteries that propel them underwater.
  • AIP is a mechanism that allows the batteries to be charged even while the boat is submerged.
  • However, even with AIP, the submarine needs to surface every three weeks or so.
  • AIP allows a submarine to remain submerged for more than a fortnight, compared to two to three days for diesel-electric boats.
  • While the six P-75 submarines are diesel-electric, they can be fitted with AIP technology later in their lives.
  • By the time P-75I is completed under the 30-year project, India is projected to have six diesel-electric, six AIP-powered, and six nuclear attack submarines (yet to be built).
  • India has been working to develop AIP technology indigenously as well.
  • In March 2021, DRDO developed the Air Independent Propulsion (AIP) System by providing the land-based prototype.
  • However, experts have certain doubts about DRDO’s AIP prototype, and many fear it may not be ready even by the time the first Kalvari Class submarine comes for refitting starting 2024.
  • Around 10 countries have developed or are close to building AIP technology, and almost 20 nations have AIP submarines.
  • There are different types of AIP mechanisms available; what India is looking for under the P-75I project is AIP based on fuel cells.
  • These cells convert chemical energy into electrical energy, recharging the batteries of the submarine.

What submarines does India have now?

  • India has 16 conventional diesel-electric submarines, which are classified as SSKs.
  • After the last two Kalvari Class subs are commissioned under P-75, this number will go up to 18. India also has two nuclear ballistic submarines, classified SSBN.
  • Of the 16 SSKs, four are of Shishumar Class, which were bought and then built in India in collaboration with the Germans starting 1980s; eight are Kilo Class or Sindhughosh Class submarines bought from Russia (including erstwhile USSR) between1984 - 2000; and four are Kalvari Class built in India at MDL.


  • There are downsides to AIP.
  • Installing AIP increases the length and weight of the boats, and requires pressurized liquid oxygen (LOX) storage onboard and supply for all three technologies.
  • Submarine’s unit cost increases by around 10%.

Exam take away

Prelims take away

  • Project -75I
  • Project 75
  • Air-Independent Propulsion technology
  • Kalvari Class submarine
  • DRDO
  • Liquid oxygen