Pakistan’s AIP Edge vs India’s Delayed Submarine Plan
Overview: A decisive undersea gap
Pakistan’s traditional submarine fleet is evolving ahead since India updated its AIP route. Three Agosta-90B vessels already have AIP in the field, and eight Hangor-class variants of the S-26 will arrive in the late 2020s to early 2030s, bringing the number to 11 AIP-capable subs. India, on the other hand, has six Kalvari-class Scorpene subs with no AIP and decisions to either continue the Scorpene line or go with a German-designed fuel-cell solution under Project 75I.
AIP makes a difference since it increases submerged endurance from approximately 48 hours to 10–14 days at patrol rates. This is achieved by reducing the number of hours spent snorkelling, reducing acoustic exposure, and maintaining contact for a longer duration. The AIP submarine fleet of the Pakistan Navy hence keeps constant pressure throughout the northern Arabian Sea and approaches to the Gulf of Oman.
Why AIP disturbs deterrence math
Air-independent propulsion fills the performance void with nuclear ships at a much reduced cost. Fuel-cell systems are very stealthy, with very minor heat and vibration. Crews can loiter, bottom, and stalk in littorals with reduced detection risk. With lithium-ion batteries, AIP enables silent persistence with periodic short-duration high-speed transits. This capability enables increased ambush potential, evasion manoeuvres, and mission endurance in both sea denial and clandestine ISR.
India’s initial focus: number of measures versus readiness.
India currently has 17 traditional conventional attack and guided-missile submarines in service. Six are new Scorpenes, acquired by India without AIPs, however. Legacy Type 209 and Kilo-class hulls still in commission are older than three decades and close to decommissioning age.
A proposal to “jumboize” these Scorpenes with an indigenous fuel-cell module has slipped. A new credible retrofit opportunity will occur with the scheduled maintenance of INS Khanderi in mid-2026, pending technology maturity.
Retrofits reduce availability for at least a year, and schedule risk multiplies when yards juggle deep refits with new-build programmes. Therefore, fleet planners must balance near-term numbers with long-term stealth.
The Scorpene extension controversy
India concluded cost negotiations on another three Scorpenes in the last financial year, but CCS approval still remains pending. Decision-makers ponder:
- Capability delta: Subsequent AIP-retrofitted up-engined Scorpenes compared to a new-build fuel cell.
- Industrial concurrency: Whether MDL can run two complex lines without slipping milestones.
- Fleet sequencing: What route delivers quiet hulls to the fleet in the minimum amount of downtime?
An extension comes with well-known supply chains and training pipelines. But successive retrofits pose the possibility of longer yard stays and fewer hulls at sea, while India requires continuous patrol coverage.
Project 75I: Design rationale and timelines
New Delhi’s transition to Project 75I, which is close to ₹70,000 crore (≈US$8.2bn), brings together Thyssenkrupp Marine Systems (TKMS) and Mazagon Dock Shipbuilders Ltd (MDL). The approach focuses on a custom Type 214 family solution with fuel cells, AIPs, and lithium-ion batteries.
Indian construction begins with Boat-1, with TKMS supplying design and core technologies and MDL executing build and integration. The schedule is projected to take approximately seven years until the first delivery, with a subsequent annual goal of delivering one boat each year.
Chief attributes are very low sound signatures, water-ram torpedo launching, and no exhaust heat plume during AIP operations. In contested littorals, these attributes determine survivability at least to an equal extent that sheer endurance does.
Pakistan’s path: Hangor-class details
The Hangor-class S-26 design is based on the Yuan family but with Pakistani modifications. Displacement increases to approximately 2,800 tonnes, length to around 76 m, and armament to six 533 mm tubes. A Stirling-cycle AIP supplements batteries to achieve multi-week submerged endurance at patrol speed.
Integrated sensors and combat systems are optimised for sea denial, including anti-surface and anti-submarine defence operations. With three Agosta-90B AIP boats in commission, deliveries of eight Hangors will redefine the regional undersea equilibrium in the next decade.
Operational implications for India
India faces a larger, quieter AIP force deployed in close-to-home waters. The reaction encompasses platforms, sensors, and doctrine:
- Accelerate 75I: Install a proven fuel-cell stack with Li-ion from the outset.
- Targeted life extension: Do not do concurrent deep retrofits that crater availability.
- ASW upgrades: scale frigate/corvette towed array sonars, increase stores of modern dipping sonars and sonobuoys for helicopters, and install fixed seabed sensors in chokepoints.
- Networked ISR: Integrate P-8I cues, coastal arrays, and unmanned undersea/surface vehicles to close the kill chain.
- Training frequency: Increase operational days at sea and perform high-fidelity drills with AIP threat profiles.
Without these changes, the AIP submarine forces of the Pakistan Navy will still enjoy time-and-space superiority and inflict greater ASW expenses upon India’s surface formations.
Technological compromises: fuel cells, Li-ion, and risk
Fuel-cell AIP remains the quiet endurance leader. Hydrogen can be generated onboard via reformers or stored safely, easing logistics. Li-ion batteries provide higher specific energy than lead-acid, allowing faster charges and longer sprint periods.
Together they offer tactical flexibility: slow, silent persistence, then short sprints to reposition or evade. India’s indigenous Air Independent Propulsion (AIP) system is strategically important, but the immediate requirement is for stealth capabilities in the field. A dual track—importing a proven stack while maturing the domestic line—balances urgency with sovereignty.
Industrial Questions: Cadence and Capability
Running two parallel lines—Scorpene extension and 75I—puts workforce and supply chain pressure. Limitations exist in module fabrication, integration bays, vendor quality control, and test ranges. Slips on MDL will cascade through the program’s schedule, removing hulls at sea.
Clean gating, believable drum beats, and yard slot prioritisation will become more important than headline orders. When faced with trade-offs, prioritising a submarine that minimises acoustic risk and maximises endurance is crucial.
The General Conclusion
Pakistan may have 11 AIP subs in commission by the early 2030s. India has none today, although it has six new Scorpenes and a future with 75I. Each year of postponement accrues risk to carrier groups, sea lines, and deterrence patrols.
India’s planners should prioritise higher weight, stealth, endurance, and cadence; they need to accelerate the 75I program, reduce retrofit downtime, and strengthen the ASW web along probable ingress routes. Carried out well, these actions close the gap—and restore undersea bargaining power.
References
- https://www.drdo.gov.in/
- https://www.thyssenkrupp-marinesystems.com/
- https://www.indiannavy.nic.in/
- https://www.naval-group.com/en
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