China’s submarine partnership with Pakistan is reshaping the Indo-Pacific balance as India faces a widening undersea capability gap
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On 14 August 2025, China launched the PNS Mangro, an export variant of its Type 039B Yuan-class submarine, for Pakistan. Built at the Wuchang Shipyard in Wuhan, it is the third vessel in Pakistan’s Hangor-class series. For Beijing, the Yuan-class is both an industrial flagship and a cornerstone of its naval export strategy. For New Delhi, however, the Mangro underscores a widening undersea asymmetry with the potential to recalibrate Asia’s maritime balance. India’s submarine fleet has slipped below minimum operational thresholds, while its role in regional subsurface capacity-building remains marginal. Reports mention India’s initiatives, at an incipient stage, of the discreet assistance to Taiwan’s indigenous programme, coupled with offers to modernise Vietnam’s Kilo-class fleet and to establish submarine-support infrastructure in the Philippines. India would require a rethink over its pattern of overpromising and underdelivering; instead, an effort to rebuild its arsenal while shaping Asia’s undersea deterrence requires urgent attention.
Pakistan’s US$5 billion Hangor-class submarines are 77 meters long with a submerged displacement of 3,600 tons and can operate at 20 knots below the surface. Powered by the Chinese Stirling Air Independent Propulsion (AIP) engines, they can dive to 300 meters, stay underwater for three weeks, and fire a combined load of wire-guided and passive-homing torpedoes, YJ-18 supersonic cruise missile (a copy of the Russian 3M-54 Club missile) and probably Babur-3 nuclear-capable cruise missiles, with the latter claiming a 450km reach. Four of these will be built in China, while the rest four will be constructed in Karachi Shipyard (KSEW) with Chinese collaboration. The key feature, the Stirling engine AIP, has played a decisive role in China’s transition from outdated coastal submarines to more advanced diesel-electric designs.
Pakistan’s US$5 billion Hangor-class submarines are 77 meters long with a submerged displacement of 3,600 tons and can operate at 20 knots below the surface.
Earlier Chinese acquisitions, including the 10 Kilo-class submarines purchased from Russia, lacked AIP and underscored the technological gap Beijing faced. Therefore, of the three primary AIP technologies available internationally, China opted to pursue the Stirling engine, considered a simpler system to develop. Even then, this path proved difficult: the China Shipbuilding Industry Corporation’s (CSIC) 711 Institute had been engaged in Stirling engine research for naval use since 1975 without producing a viable system.
A breakthrough came in the 1990s, when Beijing adopted a civilian industry approach. The Chinese sustainable energy firm Haiqi collaborated with Sweden’s Stirlingversal AB to develop Stirling engines for environmental and other civilian purposes. This partnership laid the technological foundation that was later adapted for military purposes. By 2006, China had equipped the Type 039A Yuan-class submarine with its first domestically developed Stirling AIP system. Subsequent improvements have yielded new variants for both civilian and military applications, making the Stirling engine a representative case of China’s military–civil fusion. It is a clear example of how China has leveraged foreign partnerships to accelerate its defence-industrial modernisation.
China’s navy has had a presence in the Indian Ocean since 2009, but the real inflection point came in 2013, when a Shang-class nuclear attack submarine arrived under the pretext of “anti-piracy” patrols. Since then, submarines have become a routine feature of Beijing’s deployments, often masked as piracy escorts or naval exercises. Alongside, Chinese oceanographic survey ships have turned up with growing frequency, mapping thermal clines and seabed contours around the Indian subcontinent, data critical for submarine warfare.
Moreover, Pakistan’s navy is on the cusp of a major transformation, with the induction of eight Chinese-built AIP submarines, raising its AIP fleet to 11. Beijing is outfitting Karachi Shipyard with technologies for repair and sustainment, enabling longer Chinese submarine deployments in the Arabian Sea. At Gwadar, China’s incremental control of the port is already paving the way for refuelling and replenishment of PLAN warships.
Additionally, Islamabad is not Beijing’s only partner in this region. In Bangladesh, China has delivered Ming-class submarines, and its PLA-affiliated Poly Technologies Incorporation (PTI) has built the BNS Pekua (earlier Sheikh Hasina) base at Chittagong, giving itself a forward post in the Bay of Bengal. Beijing is also positioning for a larger role in the post-Hasina era. Hambantota in Sri Lanka and Gwadar in Pakistan complete this arc of influence. For now, Colombo has tried to respect Indian sensitivities by limiting Chinese submarine calls at Hambantota or Colombo port. However, China’s debt leverage leaves open the prospect of a future naval foothold. Seen together, Chittagong, Hambantota, and Gwadar form a triangle of threat that tightens pressure on the Indian Navy and extends Beijing’s reach into India’s maritime backyard.
India’s submarine fleet is showing its age. Of 17 conventional boats, 11 are German Type 209s and Russian Kilos over three decades old, while only six are newer French Scorpenes. The Navy fields two commissioned ballistic missile submarines, with a third nearing entry, but its lone Russian-leased nuclear attack submarine was returned in 2021. Indigenous projects remain distant: the nuclear attack submarine program, cleared in 2024, promises two boats by the mid-2030s; the next batch of diesel-electric submarines under Project 75I has only recently inched into contract talks with Germany’s TKMS. The bottom line is stark: India has no AIP-equipped submarine, its nuclear attack fleet remains a decade away, two-thirds of its conventional force is nearing retirement, and any fresh induction, nuclear or conventional, lies 10 years or more in the future. In the meantime, India sails into the fastest undersea buildup in Asia with one of the weakest hands.
Beyond posing a direct threat to India, Chinese involvement in their construction, maintenance, and logistical support will entrench Beijing’s presence in the northern Indian Ocean and the Arabian Sea.
Although India has pursued active outreach in Southeast Asia, its role in submarine supply and capacity building remains marginal. When Taiwan sought assistance for its indigenous program in 2015, New Delhi, struggling with its own shortages, could offer little beyond a handful of experienced personnel. Further, India had previously trained Vietnamese submarine crews and recently, Hindustan Shipyard has proposed mid-life upgrades for Vietnam’s Kilo-class boats, leveraging its experience with India’s own fleet, while Russian yards are tied down by the war in Ukraine. In addition, India discussed with Manila in 2025 to develop submarine-support infrastructure as part of a newly minted strategic partnership. The Philippines, entering the third phase of its military modernisation, is weighing submarine acquisition, and India’s Mazagon Dockyard, with proven diesel-electric expertise, is well positioned to play a role. Yet the larger reality persists; unless India converts intent into hardware, New Delhi will remain a secondary partner in a region where Beijing is already delivering.
Submarines are considered offensive weapons, and the planned induction of eight AIP-equipped submarines armed with nuclear-capable cruise missiles will markedly alter India’s maritime security environment by 2028-30. Beyond posing a direct threat to India, Chinese involvement in their construction, maintenance, and logistical support will entrench Beijing’s presence in the northern Indian Ocean and the Arabian Sea. The operational challenge is acute: the tropical waters of the Indian Ocean already hinder submarine detection, and diesel-electric platforms with AIP systems, capable of remaining submerged for extended durations, will prove even harder to track and neutralise. To counter this evolving threat, India will have to bulk up its submarine arm while strengthening the naval capacities of its neighbours.
Atul Kumar is a Fellow at the Strategic Studies Programme, Observer Research Foundation.
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Atul Kumar is a Fellow in Strategic Studies Programme at ORF. His research focuses on national security issues in Asia, China's expeditionary military capabilities, military ...
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