Project 75I: Germany's $8 Billion Submarine Deal with India Explained

Overview

India’s Project 75(India) submarine programme aims to procure six advanced conventional attack submarines equipped with fuel-cell Air Independent Propulsion at an estimated cost exceeding ₹40,000 crore under the Strategic Partnership model. This capital acquisition bridges the Indian Navy’s underwater force deficit while transferring advanced submarine design and manufacturing technology to domestic shipyards.

The 1999 thirty-year submarine construction plan targeted a modernised fleet of 24 indigenous submarines by 2030. However, systemic procurement delays, stringent liability stipulations, and vendor attrition have stretched acquisition timelines.

Deploying proven fuel-cell propulsion remains vital to preserving sea-denial capabilities across key Indo-Pacific choke points amidst expanding regional undersea deployments by China and Pakistan.

Project 75(India), designated as P-75(I), is the Indian Navy's flagship conventional submarine procurement programme under Chapter 7 of the Defence Acquisition Procedure.

As of January 2025, bilateral defence negotiations between India and Germany reached a significant milestone. Mazagon Dock Shipbuilders Limited (MDL), partnered with Germany’s ThyssenKrupp Marine Systems (TKMS), reportedly cleared the Indian Navy’s technical field evaluation trials based on the HDW Class 214 design, according to evaluation reports published by The Hindu and SP’s Naval Forces.

Key parameters defining the current procurement phase include:

• Procurement Scope: The Ministry of Defence issued the formal Request for Proposal (RFP) for Project 75(I) on July 20, 2021, inviting bids to construct six advanced conventional submarines domestically at an estimated cost exceeding ₹40,000 crore, as detailed in a Ministry of Defence Press Release.
• Preceding Foundation: The programme builds upon the operational induction of the six Scorpene-class (Kalvari-class) diesel-electric submarines constructed under the preceding Project 75 at Mazagon Dock Shipbuilders Limited.
• Propulsion Benchmark: The tender mandates that the foreign Original Equipment Manufacturer (OEM) deliver a sea-proven fuel-cell system, addressing a critical endurance gap in India's conventional undersea fleet.

Project 75(I) is a primary test case for the Strategic Partnership (SP) model institutionalised under Chapter 7 of the Defence Acquisition Procedure (DAP) 2020. The framework builds an indigenous defence industrial ecosystem by pairing Indian shipyards with global defence manufacturers to absorb advanced design know-how and establish long-term domestic manufacturing lines.

Under the mandate approved by the Cabinet Committee on Security (CCS), Project 75(I) sets progressive indigenisation thresholds across the build cycle:

• Initial Vessel Content: According to the Ministry of Defence Project 75(I) RFP Guidelines, the procurement stipulates a minimum indigenous content of 45% for the first submarine constructed.
• Fleet End-State Target: Domestic participation must escalate systematically to achieve 60% domestic content by the sixth vessel.

The historical foundation for this acquisition traces back to July 1999, when the Cabinet Committee on Security approved the 30-year Submarine Construction Plan, as documented by the Parliamentary Standing Committee on Defence (2019–20). That blueprint envisaged a force of 24 indigenous submarines divided between conventional attack vessels (SSKs) and nuclear-powered submarines by 2030.

Project 75 successfully delivered six Kalvari-class boats—INS Kalvari, INS Khanderi, INS Karanj, INS Vela, INS Vagir, and INS Vagsheer—built by MDL in collaboration with France’s Naval Group, as confirmed in the Ministry of Defence Year End Review. Project 75(I) constitutes the planned second phase of this multi-decade roadmap.

Air Independent Propulsion is an auxiliary technology that enables conventional diesel-electric submarines to recharge battery banks and power electric drive motors without accessing atmospheric oxygen. According to DRDO Technology Focus doctrine publications, standard diesel engines require large volumes of fresh air for internal combustion, forcing conventional submarines to raise a snorkel mast above the water surface every few days.

During snorkelling, a submarine exposes its periscope mast and exhaust stream, significantly increasing its radar cross-section, thermal signature, and acoustic noise profile. This vulnerability metric is known as the indiscretion rate. Operating an operational AIP module reduces this indiscretion rate to near zero during prolonged patrol cycles, drastically enhancing vessel survivability against modern airborne Anti-Submarine Warfare (ASW) suites.

Technical evaluations generally categorise AIP implementations into two main architectures:

1. Fuel-Cell AIP Systems: Fuel cells convert chemical energy directly into electrical energy via an electrochemical reaction between hydrogen and oxygen, generating water and heat as sole byproducts. According to technical documentation from the DRDO Naval Materials Research Laboratory (NMRL), fuel cells have no major moving parts, delivering exceptional acoustic quietness, high electrical efficiency, and minimal thermal exhaust signatures.
2. Stirling Combustion Engines: Stirling cycle systems burn diesel and liquid oxygen in an external combustion chamber to drive a mechanical generator. While mechanically proven, Stirling engines generate higher vibrational noise and residual heat compared to electrochemical fuel-cell stacks.

According to reports from the Lok Sabha Standing Committee on Defence, conventional submarines must snorkel every 2 to 3 days, whereas an AIP-equipped vessel can sustain underwater endurance for two to three weeks.

To complement foreign acquisitions, DRDO's NMRL entered an agreement with Naval Group France on January 23, 2023, to complete the detailed design and integration phase for retrofitting an indigenous fuel-cell AIP module into INS Kalvari during its scheduled refit, as documented by the Ministry of Defence.

Naval forces structure their underwater fleets across distinct propulsion paradigms depending on tactical missions, operating geography, and industrial capacities.

The Indian Navy’s operating environment requires a balanced undersea architecture to counter growing coordination between regional adversaries in the Indian Ocean Region (IOR).

According to the Indian Maritime Security Strategy (IMSS-2015), the operational doctrine relies on advanced conventional submarines (SSKs) to establish sea-denial ambushes across shallow maritime choke points—including the Malacca, Sunda, and Lombok straits—while reserving nuclear attack submarines (SSNs) for wide-area blue-water surveillance and fleet escort duties.

Regional undersea developments highlight an accelerating two-front capability challenge:

• Chinese Naval Expansion: China's People's Liberation Army Navy (PLAN) currently operates the world's largest submarine fleet by vessel count, numbering over 60 hulls. According to the US Department of Defense PRC Military Developments Report, this force comprises nuclear-powered attack submarines (SSNs), ballistic missile submarines (SSBNs), and advanced Type 039A/B/C Yuan-class conventional submarines equipped with operational AIP systems. PLAN task forces deploy regularly to the northern Indian Ocean, supported by logistics infrastructure at overseas bases such as Djibouti.
• Pakistani Subsurface Modernisation: Concurrently, the Pakistan Navy is undergoing an underwater expansion via the procurement of eight Hangor-class AIP submarines under a 2015 bilateral agreement with China. According to official disclosures from Pakistan's Inter Services Public Relations (ISPR) and the Congressional Research Service, four of these vessels are being constructed at China's Wuchang Shipyard, with the remaining four built locally at Karachi Shipyard & Engineering Works (KSEW).

This concurrent expansion threatens to alter the balance of undersea capabilities in the Arabian Sea and Bay of Bengal. Timely induction of P-75(I) vessels is therefore vital to maintaining credible maritime deterrence.

The execution of Project 75(I) has faced structural hurdles under the Strategic Partnership framework. These contractual frictions explain why initial tender timelines stalled, leading to operational force-level deficits.

According to an analysis by the Manohar Parrikar Institute for Defence Studies and Analyses (MP-IDSA), the original bidding conditions mandated two strict criteria:

• The foreign OEM had to supply a sea-proven, operational fuel-cell AIP system that had already been demonstrated aboard an in-service naval submarine.
• The bidding framework imposed joint and unlimited liability clauses on the foreign vendor for overall submarine performance, despite construction taking place at an Indian shipyard outside their direct corporate management.

These rigid stipulations caused several international shipbuilders—including Naval Group (France), Saab (Sweden), and Rosoboronexport (Russia)—to formally withdraw from the P-75(I) tender. While Germany’s TKMS and Spain’s Navantia eventually emerged as participants, addressing the resulting legal and technical negotiations extended procurement cycles by several years.

This prolonged contracting phase directly impacts the force-level goals established under the 1999 Thirty-Year Submarine Construction Plan. With older Sindhughosh-class (Kilo-class) and Shishumar-class (Type 209) hulls approaching technical decommissioning, the operational gap between India's conventional fleet and the combined Chinese and Pakistani AIP force continues to widen.

Addressing the undersea force gap requires a pragmatic approach that combines expedited foreign partnerships with accelerated domestic research and development.

1. Streamlining Strategic Partnership Frameworks: The Ministry of Defence should refine liability clauses and technology-transfer milestones within the Defence Acquisition Procedure. Introducing balanced risk-sharing frameworks will prevent protracted negotiations and attract competitive global original equipment manufacturers.
2. Fast-Tracking the DRDO Indigenous AIP Retrofit: Timely execution of the January 2023 NMRL-Naval Group integration plan is essential. Successfully installing DRDO's fuel-cell AIP into INS Kalvari during its scheduled medium refit will provide a template for modernising the remaining five Scorpene-class vessels without foreign dependency.
3. Synergising Conventional and Nuclear Programmes: Conventional AIP submarines must be complemented by blue-water assets. The classified nuclear-powered attack submarine (SSN) programme approved by the Cabinet Committee on Security, as noted in the Standing Committee on Defence Demands for Grants reports, must proceed on a war footing to maintain deterrence across long-range Indo-Pacific sea lanes.
4. Expanding Private Sector Integration: Domestic private engineering firms should be integrated into the submarine supply chain. Broadening tier-2 and tier-3 supplier bases for hull fabrication, electrical power units, and combat management systems will ensure that future submarine classes achieve indigenisation targets exceeding 60%.

• Project 75(India) Mandate: Project 75(I) is a flagship Ministry of Defence programme to construct six conventional submarines with fuel-cell Air Independent Propulsion (AIP) at an estimated cost over ₹40,000 crore under the Strategic Partnership model.
• AIP Operational Value: Fuel-cell AIP systems permit conventional diesel-electric submarines to operate submerged continuously for 2 to 3 weeks, drastically decreasing the indiscretion rate associated with frequent surface snorkelling.
• Strategic Partnership Parameters: Chapter 7 of the Defence Acquisition Procedure (DAP) 2020 governs P-75(I), mandating a progressive increase in indigenous content from 45% on the initial hull to 60% on the final vessel.
• Regional Undersea Balance: India’s 30-year submarine building plan faces capability pressures as China operates over 60 submarines (including Type 039 Yuan-class AIP boats) and Pakistan inducts 8 Chinese-designed Hangor-class AIP submarines.
• Procurement Friction: Strict requirements for sea-proven AIP systems and unlimited liability terms led to vendor attrition (including Naval Group, Saab, and Rosoboronexport), contributing to procurement delays.
• Dual-Track Modernisation: Sustaining maritime deterrence requires retrofitting the indigenous DRDO-NMRL fuel-cell AIP on existing Kalvari-class hulls alongside the Cabinet Committee on Security-approved nuclear-powered attack submarine (SSN) programme.