India's submarine modernisation program represents one of the world's most complex and ambitious naval expansion initiatives, with multiple concurrent projects spanning conventional diesel-electric boats, nuclear-powered attack submarines, and autonomous underwater vehicles. The comprehensive program encompasses six major initiatives progressing at different stages, combining indigenous development with strategic international partnerships to address critical fleet modernisation requirements.

Project 75(I): Advanced Conventional Submarine Partnership

Contract Negotiations and Technical Progress: Project 75(I) has achieved a significant milestone with formal contract negotiations commencing between Mazagon Dock Shipbuilders (MDL) and Germany's ThyssenKrupp Marine Systems (TKMS) in September 2025. The partnership completed all concept design agreement services by August 31, 2025, with TKMS submitting binding offers for engineering services and advanced submarine components including air-independent propulsion systems. The ₹70,000 crore program envisions constructing six next-generation diesel-electric submarines based on the Type 214 design at MDL facilities in Mumbai under the Strategic Partnership model.

TKMS has entered strategic partnerships with Indian firms to achieve these targets, including a memorandum of understanding with VEM Technologies signed on September 3, 2025, for heavyweight torpedo development, production, integration, and testing. Additional collaboration with Atlas Elektronik focuses on anti-submarine warfare systems for surface vessels.

Project 75(AS): Stopgap Submarine Initiative

Fleet Gap Management: Project 75(AS) represents a critical stopgap measure involving construction of three additional modified Kalvari-class submarines at MDL to address the Navy's ageing submarine assets and maintain operational strength. The program was conceived due to delays and rising costs in other submarine programs, particularly Project 75(I). However, the anticipated contract signing by March 2025 has not materialised, placing the project in a precarious position within India's procurement processes.

The modified Kalvari-class boats would provide breathing space until Project 75(I) submarines become operational, maintaining the Navy's conventional submarine fleet strength amid regional security challenges. The program demonstrates the interconnected nature of India's submarine acquisition strategy, where delays in one project necessitate parallel initiatives to maintain operational capabilities.

Project 76: Indigenous Conventional Submarine Development

Design Phase Acceleration: Project 76 has gained substantial momentum since 2024, with L&T Defence founder JD Patil confirming that design finalisation is expected within one year of the current timeline. The program represents India's first truly indigenous conventional submarine design, developed collaboratively between L&T, the Navy's Directorate of Naval Design (Submarine Design Group), and DRDO. Preliminary design work is progressing rapidly, with completion targeted for 2026-27.

Technical Specifications And Capabilities: The Project 76 submarines will feature approximately 3,000-ton displacement with integrated air-independent propulsion systems, advanced sonars, and indigenous torpedo tube-launched cruise missile capabilities. The program plans six submarines with 95% indigenous content, emphasising complete self-reliance in submarine technology. Construction of the first submarine is expected to commence around 2030, with launch projected by 2037.

Indigenous System: Both MDL and L&T are developing conventional submarine design capabilities through midget submarine projects as stepping stones. MDL launched its experimental "Arowana" midget submarine in May 2024 as a proof of concept, while simultaneously working on full-scale indigenous conventional submarine design completion by 2028. L&T's SOV400 midget submarine design, certified by a European firm, demonstrates the company's technical competence in underwater platform development.

Project 77: Nuclear-Powered Attack Submarines

Strategic Nuclear Capability: Project 77, formerly Project 75 Alpha, received Cabinet Committee on Security clearance on October 9, 2024, for developing two nuclear-powered attack submarines with an estimated cost of ₹40,000 crore. The program envisions six SSNs total, with the first two submarines scheduled for completion by 2036-37, followed by additional vessels in 2038-39. These submarines will feature 95% indigenous content with a 190 MW pressurised light-water reactor developed by the Bhabha Atomic Research Centre.

Advanced Operational Concepts: Project 77 submarines will integrate manned-unmanned operational concepts, incorporating advanced unmanned underwater vehicles like the 20-ton JALKAPI-XLUUV. The submarines will feature nearly 10,000-ton displacement, maximum speeds exceeding 30 knots, and armament including BrahMos missiles, future hypersonic weapons, and Varunastra heavyweight torpedoes with strike ranges between 1,500-2,000 kilometres.

Autonomous Underwater Vehicle Development

XLUUV Program Progress: The Indian Navy's Extra Large Unmanned Underwater Vehicle (XLUUV) program, designated JALKAPI-XLUUV, is approaching operational readiness with induction expected within 1-2 years according to DRDO Chairman Dr. Samir V Kamat. The 20-ton displacement vehicle features 30-45 day endurance capabilities and operates at depths up to 300 meters. The Navy requires up to 12 XLUUVs for intelligence, surveillance, reconnaissance, anti-submarine warfare, and mine countermeasures missions.

The High Endurance Autonomous Underwater Vehicle developed by DRDO's Naval Science & Technological Laboratory successfully completed lake trials in March 2025, demonstrating flawless performance in surface and submerged conditions. The 6-ton HEAUV features 15-day endurance at 3 knots with maximum speed of 8 knots, incorporating modular payloads, advanced sonar systems, and communication capabilities. The Navy plans to operate 20 HEAUVs to enhance underwater operational capabilities.

Summing up, the convergence of these six major submarine initiatives represents India's most ambitious naval modernisation effort, combining immediate operational needs with strategic indigenous capability development across conventional submarines, nuclear-powered vessels, and autonomous underwater platforms.

IDN (With Agency Inputs)