Scorpene subs to get advanced air-independent propulsion for endurance

With no foreign submarine acquisitions in sight, India to upgrade existing fleet

As INS Vagir, the fifth Scorpene (Scorpion in French) submarine built by Mazagon Docks Limited (MDL), Mumbai, was commissioned into the Indian Navy on Monday, the Ministry of Defence (MoD) announced that the air independent propulsion (AIP) developed by the Defence R&D Organisation (DRDO) would be reverse-integrated into the fleet of six Scorpenes.

“In a major boost to ‘Aatmanirbhar Bharat’, fuel cell-based AIP system of DRDO’s Naval Materials Research Laboratory (NMRL) will soon be fitted onboard INS Kalvari (the first of six Scorpene submarines built by MDL,” said a MoD press release.

Senior officials of NMRL and Naval Group (France) signed an agreement in Mumbai to cooperate in the detailed design phase for integrating the DRDO’s AIP into the six Kalvari-class submarines. It is agreed that Naval Group France is to certify the indigenous AIP design for integration in the submarines, said the MoD.

An AIP multiplies the lethality of a diesel-electric submarine by multiplying its endurance for operating submerged. Conventional diesel-electric submarines, such as the ones the Indian Navy operates, must surface to charge their batteries after about 48 hours of operation. However, a submarine with AIP can operate submerged for up to 14 days.

The AIP developed by the NMRL is called “fuel cell based AIP” and is unique in generating its requirement of hydrogen onboard.

“This technology has been successfully developed by NMRL with the support of Indian industry partners. The technology has now reached the stage of maturity for industrialization,” stated the MoD.

The land-based prototype of the NMRL’s AIP has been tested successfully. According to the MoD, the next step will be the “detailed design certification of the energy module,” which NMRL will do along with Indian industry partners.

Naval Group has undertaken to oversee the integration of the indigenous AIP inside the Scorpenes, leading to “localisation and industrialization of AIP including the hull fabrication by the Indian industry for future fitment on-board the submarines,” announced the MoD.

The Naval Group head, Pierre Eric Pommellet, said this was “a natural extension of the strategic bilateral cooperation between India and France in the field of underwater defence and deterrence.”

Project 75 is the MoD’s code-name for the construction of six Scorpene submarines in MDL with technology supplied by French shipbuilders, Naval Group (earlier Armaris, and then DCNS. Project 75 delivered its first submarine, INS Kalvari, in December 2017.

That was followed by four more boats (as the navy refers to submarines), called the Kalvari-class after the lead vessel. These included INS Khanderi (commissioned in September 2019), INS Karanj (March 2021), INS Vela (November 2021) and INS Vagir (January 2021).

The sixth and last Project 75 submarine, INS Vagsheer, is currently completing her sea trials in order to be delivered in 2024, says the MoD.

That will enhance up to 17 the number of Indian Navy submarines. These include seven Russian-origin Kilo-class, four German origin, HDW Type 209 submarines and six Scorpenes. There is also one Akula class, nuclear-propelled boat, taken from Russia on lease.

According to the MoD’s 30-year submarine building programme, Project 75 was intended to be followed by Project 75-India, which involved building six more AIP-propelled submarines in India, with technology provided by a chosen global shipbuilder.

Project 75-India was to be followed by an indigenous project to build 12 more conventional, AIP-propelled submarines.

Now, however, with the DRDO’s AIP heading for operational viability, Project 75-India will involve the DRDO’s AIP, not a foreign one.

In parallel to the construction of these 24 conventional submarines, the DRDO is developing a line of six nuclear propelled, conventionally armed attack submarines (SSNs).

Speaking at the commissioning of INS Vagir, Laurent Espinasse of Naval Group said Project 75 highlights the success of India’s indigenous submarines construction programme. “This submarine has been completely built by MDL having successfully absorbed the technology transfer from Naval Group, in line with the ‘Make in India’ policy,” he said.

Building six Scorpene submarines has promoted highly trained micro, small and medium enterprises (MSMEs). “MDL and Naval Group have developed a rich industrial ecosystem of more than 50 Indian companies, along with an Indian subsidiary with more than 70 Indian engineers to support Indian Navy, thus contributing to industrial and technological sovereignty,” stated Naval Group.

The Scorpene is a 2,000-tonne, conventional-propulsion, stealthy and high-performance submarine, which Naval Group has optimised for anti-surface vessel warfare, anti-submarine warfare, long-range strikes, special operations and intelligence gathering.

Stealthy and fast, its high level of automation allows it to be operated by a limited number of crew, which reduces its operating costs significantly. Its combat edge is provided by six weapon launching tubes and 18 weapons, including torpedoes and missiles.

When the Vagsheer is delivered, there will be 14 Scorpene submarines in service in four navies: two each in Chile and Malaysia, four in Brazil and six in India. In addition to these, potential buyers include the Philippines, Indonesia and Romania.