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Post at: Jul 30 2022

Air Independent Propulsion (AIP) System

Recent Context

  • On 3rd May 2022 French company Naval Group has announced that it is unable to participate in Government of India’s  P-75I project due to conditions mentioned in the request for proposal (RFP) related to Air Independent Propulsion (AIP) system.

Origin of The Project

  • Around the time of the Kargil war, Government of India approved a 30- year submarine building plan. It included the construction of 24 submarines indigenously by 2030.
  • The submarine building plan had separate series of submarine building lines with code names Project 75 and Project 75I.
  • 30-year submarine building plan called for two parallel production lines, each constructing six submarines. The older Project-75 (P-75) was brought under the new plan.
  • The two production lines to be built under P-75 and P-75I using transfer of technology (ToT) from different foreign manufacturers.

  • Currently out of Five foreign Original Equipment Manufacturers (OEM) selected by MoD for the project , only two (South Korean Daewoo Shipbuilding and Marine Engineering and Spain’s Navantia) have remained. 

What is Air Independent Propulsion (AIP) System?

  • AIP is a Marine propulsion technology for conventional non-nuclear submarines.
  • It is a marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen (by surfacing or using a snorkel).
  • If fitted with an AIP system, the submarine will need to take in oxygen only once a week.

Advantages of AIP over Legacy diesel-electric Propulsion

  • Legacy diesel-electric submarines operate silently underwater for up to 48 hours, but they have to surface within restricted hours to run a generator that recharges their batteries.
  • When they surface, become vulnerable to detection by enemy radar.
  • AIP system reduces this vulnerability as it enables underwater operations for up to two weeks.

Fuel Cell Based AIP system

  • In a fuel cell based AIP, an electrolytic fuel cell releases energy by combining hydrogen and oxygen, with only water as the waste product ensuring less marine pollution.
  • The cells are highly efficient, and do not have moving parts, thus ensuring that the submarine has a low acoustic emission of sound.

Disadvantages of AIP System

  • Installation increases the length and weight of the boats
  • Requires pressurised liquid oxygen (LOX) storage on-board and supply 
  • Submarine’s unit cost increases by around 10%

Current Uses of this Tech

  • Around 10 countries have developed or are close to building AIP technology, and almost 20 nations have AIP submarines.
  • India’s DRDO have also developed this technology which is a modular one but currently only being compatible to P-75 project submarines.



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