German or Spanish submarine? Indian Navy's choice depends on the best AIP

While conventional diesel-electric submarines can operate underwater for no more than 48 hours, those with AIP can remain underwater for up to two weeks before they must surface for battery charging

Mumbai-based Mazagon Dock Ltd (MDL) is poised to deliver to the Indian Navy the last of six Scorpene, Kalvari-class, diesel-electric submarines built under the Project 75 programme. Now attention is shifting to Project 75(I), the programme to build another six submarines powered by Air Independent Propulsion (AIP).

 

These are running far behind the timeline in the Ministry of Defence’s (MoD’s) 30-Year plan, approved by the Cabinet in 1999, to build 24 conventional submarines by 2029. With the technology and experience acquired from Project 75 and Project 75(I), Indian designers and shipyards are to build the remaining 12 submarines in India as Project 76 — a fully indigenous effort, from design to delivery, with no foreign support. 

 

While conventional diesel-electric submarines can operate underwater for no more than 48 hours, submarines with AIP can remain underwater for up to two weeks before they must surface for battery charging. That provides significant operational advantages over legacy diesel-electric submarines, which are easily detected by enemy radar, which spots masts or snorkels protruding out of the water while they recharge batteries.

 

The tender for Project 75(I) is also crucial for Project 76 in three critical ways. First, the foreign partner chosen for Project 75(I) — designated the “original equipment manufacturer”, or OEM — must demonstrate possession of a fuel cell-based AIP system that is operational on board a submarine at sea. Second, the OEM must be willing to transfer the entire submarine design to India. Third, Project 75(I) is required to be processed under the Strategic Partnership (SP) model, described in Chapter 7 of the Defence Procurement Procedure of 2016 (DPP - 2016).

 

There was initially keen interest among submarine OEMs in a project that was worth $10-15 billion, but that petered out. After the RFP was issued in 2021, just two consortia remained in the fray. The first, led by MDL in partnership with Thyssenkrupp Marine Systems, Germany (TKMS), is offering the Type 212 submarine. The other, which is led by Larsen and Toubro (L&T) in partnership with Spanish shipyard Navantia, is offering the S-80 submarine.

 

Predictably, the contest boils down to a simple question: Which OEM is offering the better AIP. In recent months, the public relations machinery of MDL-TKMS, as also that of L&T-Navantia, have been claiming vociferously that their respective submarines have conclusively proven to be the superior one.

 

The MoD, in its technical evaluation, will have the job of determining which of the two is better. The RFP stipulates that both OEMs must prove their AIP system’s performance on board a submarine at sea. TKMS did so successfully during its Field Evaluation Trials (FET) in March 2024. Navantia, which has neither a proven AIP system nor a system installed on board a submarine, was unable to do so during its FET in June 2024.

 

MDL-TKMS partnership

 

TKMS’s success came as no surprise to the navy, which has operated four of its submarines since the 1980s. These Shishumar-class, diesel-electric attack submarines, which are still in active service with the Indian Navy, are an Indian variant of the Type 209 submarines developed by the German yard Howaldtswerke-Deutsche Werft (HDW) under the internal designation “Type 1500”.

 

TKMS has 25 years of experience in operating AIP-equipped submarines at sea, including with the navies of Germany, Italy, Greece, Turkey, Singapore, Israel, Portugal, Greece and South Korea. These are fitted on diverse classes of TKMS submarines, including the Type 209, Type 212, Type 212 NFS, Type 214 and the Type 218. At present, the company is working on a joint Germany-Norway programme for constructing six Type 212 CD submarines. South Korea’s latest submarines operate TKMS fuel cell AIP systems which have been derived from the German design. 

 

TKMS has collaborated with numerous countries’ navies, developing cooperation models in accordance with their requirements. Its successful partnerships with South Korea, Italy, Turkey and Israel are different from each other, ranging from full design transfer (South Korea and Italy) to maintenance transfer of technology (MToT), which Israel demanded. 

 

MDL, the proposed Indian partner to TKMS, also has a proven record in submarine construction. In the late 1980s-early 1990s, in partnership with TKMS, MDL pioneered indigenous submarine construction with the commissioning of two conventional boats, INS Shalki in 1992 and INS Shankul in 1994. These Type 209 submarines, which were modified to meet Indian requirements, continue to serve as frontline platforms more than three decades later.

 

Technology sharing between MDL and TKMS has been so successful that none of the Indian Navy’s four Type 209 submarines have ever had to return to Germany for repairs, refits, modernisation or life extension certification, all of which have been undertaken by MDL. In contrast, India’s 10 Russian Kilo-class submarines, which were acquired at the same time, have been back to Russia numerous times for refits and modernisation. 

 

MDL also has the advantage of an operational production line after taking two decades for building six Scorpene submarines. This has given MDL a qualified and experienced work force, and a management that is sensitive to the nuances of submarine construction.

 

In the case of Project 75(I), where a high level of indigenisation has been demanded, a robust eco-system of Indian ancillary industries has been qualified and has delivered the requisite quality of indigenous equipment for the ongoing Project 75 programme. This experience and infrastructure, built up over decades, represents a huge investment and resource for India. 

 

There is no “off the shelf” submarine that can meet the Indian Navy’s requirements. Any designs have to be modified to meet a customer’s requirements. India is a demanding customer with its extensive experience in submarine operations — hence there is considerable design work to be undertaken. MDL and TKMS are already developing a design which includes not only the Indian Navy’s specific requirements but also incorporates advanced stealth features from TKMS’ other contemporary designs. 

 

L&T–Navantia partnership

 

Navantia, the Spanish shipyard, has been struggling for over a decade to develop its S-80 design to meet its own requirements. The first of the S-80 class, named Isaac Peral, was commissioned last year after almost 14 years under construction. This submarine had to be extensively modified with US assistance, as the original design was faulty and too heavy. The design had to be lengthened to meet the additional weight, which in turn led to a situation where the submarine pens at the Spanish Navy base at Cartagena had to be redesigned to accommodate these larger submarines. 

 

After these hiccups, the S-80 programme is underway with the second submarine likely to get commissioned soon. The Spanish have also designed a fuel cell AIP system which they are offering for the P75(I) programme. 

 

At present, the Spanish AIP is only working as a laboratory model and is yet to be installed on board a submarine. The Spanish navy has decided to install its AIP only on the third submarine, which is likely to be commissioned in 2026, at the earliest. 

 

That means the first Spanish AIP system will become operational only after successfully completing its sea trials on board that submarine.  This could take years, since demonstrating a laboratory model under perfect conditions is far easier than proving an AIP on board a submarine at sea with all its constraints of space, routing of pipelines, accessibility, ergonomic positioning of operator panels, temperature conditions, vibrations and interfacing with the other submarine systems on board.

 

 “The L&T-plus-Navantia proposal for P75(I) is fully compliant and in line with extant policy and procedures… Field evaluation trials (FET) were conducted on Navantia’s AIP in mid-2024. During this FET the AIP powered an operational submarine of same class and part of the Spanish Navy fleet…The submarine also performed full scale sea-sortie, including simulating upset operating conditions to demonstrate the ease and flexibility of recovering the submarine to normal operation, using the AIP power stored in the batteries, with Indian Navy team on-board,” stated Jayant Patil,  Advisor Defence & Smart Technologies to CMD Larsen & Toubro, in response to Business Standard’s request for comments.

 

There was no response from MDL, TKMS, Navantia or the Indian MoD.

 

Spain has no experience in exporting a submarine, nor any experience in transferring technology for developing an indigenous weapons capability in another country. L&T, its Indian partner, is an industrial giant but with no experience in constructing conventional submarines.

 

Spain is currently grappling with its own programme which has run far beyond its stipulated cost and time. There is no certainty of success in the complex task of developing a modified design for the Indian requirements.

 

What is at stake

 

> With Mazagon Dock poised to deliver the last of six Scorpene submarines, attention shifts to Project 75(I), the programme to build another six submarines powered by AIP

 

> These are running far behind the timeline in the Ministry of Defence’s 30-Year plan to build 24 conventional submarines by 2029

 

> Indian designers and shipyards are to build the remaining 12 submarines in India as Project 76 — a fully indigenous effort

 

> Conventional diesel-electric submarines can operate underwater for no more than 48 hours, but submarines with AIP can remain underwater for up to two weeks

 

> That provides significant operational advantages over legacy diesel-electric submarines, which are easily detected by enemy radar when they surface to recharge batteries