The Indian Navy’s long-delayed submarine force modernization is approaching a pivotal turning point. In an official briefing, Defence Secretary Rajesh Kumar Singh confirmed that the central government has advanced to the final stage of approving an acquisition valued at over ₹80,000 crore to construct six next-generation conventional submarines under Project-75(India), while concurrently evaluating a proposal to build three additional Kalvari-class (Scorpene) submarines.
The confirmation marks the culmination of more than two decades of planning under the government’s 30-Year Submarine Construction Plan approved in 1999. The plan envisioned a 24-boat conventional submarine fleet operating alongside nuclear-powered ballistic missile submarines (SSBNs) and nuclear-powered attack submarines (SSNs).
With legacy Soviet-era Sindhughosh-class (Kilo) and Shishumar-class (Type 209) hulls entering late-stage service life, the Ministry of Defence is leveraging a dual-track strategy: using follow-on Scorpene orders to immediately keep domestic assembly docks active, while initiating the larger, technologically superior Project-75(I) production line.
The Dual Procurement Blueprint: P-75(I) vs. Follow-On Scorpenes
The two submarine programs serve complementary operational and industrial roles within the Indian Navy’s force architecture:
[ INDIA'S DUAL-TRACK SUBMARINE PROCUREMENT ]
PROJECT-75(I) [PRIMARY HIGH-TECH PLATFORM] FOLLOW-ON SCORPENE ORDER [INTERIM BRIDGE]
┌───────────────────────────────────────────┐ ┌───────────────────────────────────────────┐
│ • Scale: 6 Advanced SSKs │ │ • Scale: 3 Additional Kalvari-class SSKs │
│ • Cost: >₹80,000 Crore │ │ • Cost: ~₹20,000 Crore (Estimated) │
│ • Foreign Partner: TKMS (Germany) │ │ • Foreign Partner: Naval Group (France) │
│ • Domestic Yard: Mazagon Dock (MDL) │ │ • Domestic Yard: Mazagon Dock (MDL) │
│ • Key Tech: Fuel-Cell AIP from Day 1, │ │ • Key Tech: Mature production line, │
│ Heavyweight Torpedoes, Land-Attack │ │ proven hot-and-shallow IOR performance, │
│ Cruise Missiles (LACM) │ │ slated for indigenous DRDO AIP refit │
└─────────────────────┬─────────────────────┘ └─────────────────────┬─────────────────────┘
│ │
└──────────────────────┬───────────────────────┘
│
▼
[ UNDERWATER FLEET STRENGTHENED ]
Arrests declining squadron strength;
establishes continuous domestic fabrication
1. Project-75(India): The ₹80,000-Crore Milestone
Project-75(I) represents one of the largest and most complex defense procurement programs ever undertaken in India under the Strategic Partnership (SP) model.
Addressing the status of the mega-deal, Defence Secretary Rajesh Kumar Singh noted:
“Both Project-75(I) and additional Scorpene submarines are being considered. Project-75(I) is at the final stage. It has been submitted and is pending a final decision by the competent authority. Additional Scorpene submarines are also being considered. It is not as advanced as the other one, but that is also under consideration.”
+─────────────────────────────────+──────────────────────────────────────────────────────────+
| Program Parameter | Project-75(India) Specification |
+─────────────────────────────────+──────────────────────────────────────────────────────────+
| Total Vessels Planned | 6 Advanced Diesel-Electric Attack Submarines (SSKs) |
| Estimated Program Cost | > ₹80,000 Crore (~$9.6 Billion) |
| Lead Domestic Shipyard | Mazagon Dock Shipbuilders Limited (MDL), Mumbai |
| Foreign Technology Partner | Thyssenkrupp Marine Systems (TKMS), Germany |
| Selected Design Baseline | HDW Class 214 / Type 212CD Derivative |
| Air-Independent Propulsion | High-capacity Polymer Electrolyte Membrane (PEM) Fuel Cell|
| Primary Weapon Systems | Wire-guided heavyweight torpedoes, BrahMos/LACM missiles |
| Current Approval Stage | CNC negotiations complete; awaiting CCS clearance |
+─────────────────────────────────+──────────────────────────────────────────────────────────+
The Technology Edge: Sea-Proven AIP
A non-negotiable requirement of the Navy’s Request for Proposal (RFP) was an operational, sea-proven Air-Independent Propulsion (AIP) system. AIP technology allows a conventional submarine to generate electrical energy underwater without accessing atmospheric oxygen via a snorkel mast, extending submerged endurance from 3–4 days to more than two to three weeks.
The TKMS fuel-cell AIP system—proven across operational navies in Germany, Italy, Portugal, and Greece—operates silently with no moving parts and generates negligible thermal signatures, giving the boats deep acoustic stealth.
2. The Three Follow-On Scorpenes: Bridging the Capability Void
While Project-75(I) progresses toward Cabinet approval, constructing the first submarine under a new class typically requires six to eight years from contract signing to commissioning. To prevent the loss of skilled submarine manufacturing labor at Mazagon Dock following the delivery of the sixth Scorpene boat (INS Vagsheer), the Navy has pursued an order for three additional Scorpene-class submarines.
- Warm Production Line: MDL’s submarine assembly bays, precision welding jigs, and specialized supplier ecosystem can transition immediately into hull fabrication without multi-year shipyard retooling.
- Standardized Operations: The Indian Navy already operates six Kalvari-class boats (Kalvari, Khanderi, Karanj, Vela, Vagir, Vagsheer). Inducting three more creates a robust 9-boat fleet with established training, maintenance, and logistics chains.
- Indigenous Content Surge: Unlike the early batch of Scorpenes, the follow-on batch is slated to integrate higher domestic content, including indigenous communications suites, advanced sonar processing, and domestic electronics.
Indigenization Pipeline: DRDO AIP and NPOL Combat Systems
Alongside new hull construction, Indian defense research establishments are completing modular technology upgrades for submarines already in active service:
[ INDIGENOUS TECHNOLOGY PLUGS ]
DRDO PHOSPHORIC ACID AIP NPOL INTEGRATED COMBAT SYSTEM
┌──────────────────────────────────────┐ ┌──────────────────────────────────────┐
│ • Developed by Naval Materials │ │ • Developed by Naval Physical and │
│ Research Laboratory (NMRL/DRDO). │ ────► │ Oceanographic Laboratory (NPOL). │
│ • Uses on-board hydrogen generation │ │ • Indigenous open-architecture │
│ from sodium borohydride. │ │ sonar and target-motion analysis. │
│ • Scheduled for mid-2027 refit on │ │ • Replaces foreign proprietary │
│ first Kalvari-class submarine. │ │ systems during routine dockings. │
└──────────────────────────────────────┘ └──────────────────────────────────────┘
The Defence Secretary highlighted that the DRDO-developed AIP plug will be retrofitted into the lead boat, INS Kalvari, during its first major refit scheduled for the middle of next year:
“The DRDO has developed an indigenous AIP system, which the Navy plans to install on one of its Scorpene-class submarines during a mid-life refit around the middle of next year… We are going to start putting that in all of our submarines over time, as they come in for refits. That will again be a major game changer when it comes to improving the combat capabilities of our submarines.”
Simultaneously, the indigenous combat management system engineered by NPOL in Kochi will replace imported proprietary French systems across the fleet, giving India full sovereign control over weapon fire-control algorithms and acoustic signatures.
Strategic Imperative: The Indian Ocean Undersea Race
India’s submarine push is driven by shifting undersea balances in its primary maritime theater of interest:
[ REGIONAL UNDERSEA POWER BALANCE ]
PAKISTAN NAVY RECAPITALIZATION CHINESE PLA NAVY EXPANSION
────────────────────────────────────── ──────────────────────────────────────
• 8 Hangor-class (Type 039B) AIP-equipped • World's largest naval force by hull count;
submarines being inducted (4 built in operates >60 conventional & nuclear subs.
China, 4 at Karachi Shipyard). • Regular forward deployments of Yuan-class
• First hull launched; delivers long-range (Type 039A/B) AIP submarines into the IOR
underwater strike across Arabian Sea. supported by deep-water bases (Djibouti).
- The Hangor Challenge: The Pakistan Navy is progressively receiving eight Hangor-class AIP submarines from China. These platforms will significantly upgrade Pakistan’s anti-access/area-denial (A2/AD) capabilities along critical energy shipping lanes outside the Gulf of Oman and the Strait of Hormuz.
- Force Level Attrition: The Indian Navy operates 16 conventional submarines, but nearly half the fleet consists of Type 209s and Kilo-class boats that are more than 30 years old and undergoing life-extension refits. Reaching the approved force level of 18–24 modern conventional attack boats requires simultaneous construction programs.
What Happens Next: Key Procurement Milestones
Over the next 6 to 12 months, the Indian naval modernization drive will track three critical institutional decisions:
- Cabinet Committee on Security (CCS) Sanction: Formal financial clearance from the Prime Minister-led CCS for the ₹80,000-crore Project-75(I) deal, followed by contract signing between the Ministry of Defence, Mazagon Dock, and TKMS.
- Acceptance of Necessity (AoN) for Extra Scorpenes: The Defence Acquisition Council (DAC), chaired by Defence Minister Rajnath Singh, reviewing commercial cost terms to issue the final commercial award for the three follow-on Scorpene boats at MDL.
- INS Kalvari Docking for AIP Hull Cut: Commencing dry-dock hull modifications on INS Kalvari in mid-2027 to insert the DRDO-developed AIP plug, validating India’s capability to integrate indigenous propulsion into foreign-designed pressure hulls.
Frequently Asked Questions
What is India’s ₹80,000-crore Project-75(I) submarine program?
Project-75(India) is a strategic defense acquisition project to build six advanced conventional diesel-electric attack submarines inside India. The program features sea-proven Air-Independent Propulsion (AIP), advanced stealth, and land-attack cruise missile capabilities, executed via a partnership between Mazagon Dock Shipbuilders Limited (MDL) and Germany’s Thyssenkrupp Marine Systems (TKMS).
Why is India also considering three additional Scorpene submarines?
Constructing the new Project-75(I) submarines will take several years to set up. Ordering three additional Scorpene (Kalvari)-class boats from Mazagon Dock bridges the capability gap, prevents shipyard assembly lines from going idle, and quickly adds force strength to counter growing naval assets in the Indian Ocean.
What is Air-Independent Propulsion (AIP) and why does it matter?
Conventional diesel-electric submarines must periodically surface or snorkel to take in oxygen to run their diesel generators and recharge their batteries, making them vulnerable to radar and satellite detection. AIP allows a submarine to remain completely submerged for two to three weeks at a time, drastically reducing its detection signature.
When will the indigenous DRDO AIP system be installed?
According to Defence Secretary Rajesh Kumar Singh, the DRDO-developed fuel-cell AIP system will be retrofitted into the first Scorpene submarine (INS Kalvari) during its planned major mid-life refit around the middle of 2027.
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