Taiwan’s First Indigenous Hai Kun SS-711 Submarine Completes Sixth Sea Trial.

Taiwan’s first indigenous defense submarine, Hai Kun SS-711, completed its sixth sea trial off Kaohsiung on February 16, 2026, focusing on shallow-water pre-immersion testing. The milestone moves the island closer to operational deployment of a domestically built submarine designed to strengthen its undersea deterrent against regional threats.

Taiwan’s Ministry of National Defense confirmed on February 16, 2026, that Hai Kun SS-711, the island’s first indigenous defense submarine, completed its sixth sea trial off Kaohsiung, concentrating on shallow-water pre-immersion testing under close naval supervision. The trial evaluated sonar calibration, propulsion responsiveness, hull integrity, and velocity control systems, all critical checks before authorizing deeper dives and full operational certification. Defense officials described the phase as technically sensitive, as it validates the submarine’s acoustic profile and maneuverability in coastal waters where Taiwan expects the vessel to operate.
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Taiwan Hai Kun SS-711 submarine conducts its sixth sea trial off Kaohsiung, validating sonar, propulsion, and shallow-water maneuvering systems ahead of deep-dive certification. (Picture source: Social Network)

The sixth sortie focused on evaluating the submarine’s combat and platform systems under realistic littoral conditions. Taiwan’s coastal waters are acoustically complex, characterized by dense commercial shipping lanes, fishing activity, salinity stratification, and uneven seabed topography. Engineers closely monitored the performance of the bow-mounted and flank sonar arrays, assessing detection range stability, signal clarity, and processing reliability in environments saturated with background noise. For a diesel-electric submarine intended to operate in confined and contested waters, sonar precision is not merely a technical parameter but the foundation of its survivability and lethality.

Propulsion testing formed another pillar of the sea trial. Hai Kun is assessed to use a conventional diesel-electric propulsion architecture optimized for low acoustic signature rather than sustained high-speed blue-water transit. During the trial, naval engineers measured vibration levels, shaft alignment tolerances, and machinery noise output across variable load conditions. Particular attention was given to quieting measures that reduce detectable acoustic emissions, a decisive requirement given the People’s Liberation Army Navy’s growing anti-submarine warfare network of surface combatants, maritime patrol aircraft, and seabed sensors operating in the Taiwan Strait.

Velocity and buoyancy control were also scrutinized in shallow-water scenarios, where the margin for error is significantly narrower. Controlled speed modulation and trim adjustments are critical during depth transitions, especially in littoral environments where bathymetry changes rapidly. The pre-immersion testing phase simulated operational maneuvers that require a precise balance between stealth, maneuverability, and safety. Successful completion of this stage indicates growing confidence in the submarine’s ballast systems and digital control architecture ahead of deeper dives.

Hai Kun SS-711 represents the flagship achievement of Taiwan’s Indigenous Defense Submarine program, a strategic initiative revived after decades of stalled procurement attempts abroad. Constructed by CSBC Corporation in Kaohsiung using modular shipbuilding techniques, the submarine embodies Taipei’s effort to localize critical defense production amid diplomatic isolation and mounting cross-Strait pressure. While official specifications remain classified, defense analysts estimate submerged displacement of 2,500 to 3,000 tons, placing it in the medium-conventional submarine category.

The platform is widely expected to integrate U.S.-origin Mk 48 heavyweight torpedoes, providing credible anti-surface and anti-submarine strike capability. Reports also suggest the potential integration of submarine-launched anti-ship missiles, which would significantly expand the engagement envelope against hostile surface action groups or amphibious assault formations. The combat management system reportedly incorporates Western-sourced components, allowing networked targeting and coordination with Taiwan’s surface fleet and coastal missile units while maintaining operational discretion regarding supplier identities.

The strategic significance of Hai Kun becomes clearer when viewed against Taiwan’s aging submarine inventory. Before the Indigenous Defense Submarine program, the Republic of China Navy relied primarily on two Dutch-built Hai Lung-class submarines delivered in the 1980s, supplemented by legacy boats derived from mid-20th-century designs, which were used largely for training. Political constraints repeatedly obstructed foreign submarine acquisitions, compelling Taiwan to invest in domestic industrial capacity. Hai Kun, therefore, symbolizes both a technological milestone and a strategic declaration of self-reliance.

Its emergence aligns with a broader modernization of Taiwan’s navy centered on asymmetric warfare and distributed lethality. Rather than pursuing fleet parity with the numerically superior People’s Liberation Army Navy, Taipei has prioritized survivable, high-impact platforms capable of denying sea control. The navy has introduced Tuo Chiang-class stealth missile corvettes armed with Hsiung Feng II and III anti-ship missiles, expanded mobile coastal defense cruise missile batteries, and deployed fast minelayers to secure maritime approaches rapidly. Existing surface combatants, including Kidd-class destroyers and Cheng Kung-class frigates, are undergoing upgrades to their radar, electronic warfare, and air-defense systems to enhance layered resilience against missile-saturation threats.

Within this framework, submarines function as force multipliers. Even a limited number of quiet diesel-electric boats can impose disproportionate operational costs on an adversary by forcing allocation of anti-submarine assets and creating persistent uncertainty beneath the surface. In narrow waterways such as the Taiwan Strait, where maritime transit routes are predictable and geographically constrained, undersea ambush capability becomes a powerful deterrent factor.

Naval observers emphasize that shallow-water validation is often one of the most technically challenging phases in a submarine’s development cycle. Acoustic distortion, traffic density, and hydrological variability can degrade system performance in ways not evident during dockside testing. The successful execution of the sixth sea trial, therefore, signals more than procedural progress; it demonstrates that Taiwan’s indigenous platform is steadily maturing into an operational asset capable of operating in the very environment in which it would most likely be deployed.

Further trials are expected to include deeper dives, extended endurance assessments, and eventual live-fire weapon validation before formal commissioning. Additional submarines are planned under the Indigenous Defense Submarine program, with each successive hull anticipated to incorporate refinements derived from ongoing sea trials, including improvements in acoustic damping and potential enhancements to energy storage systems to extend submerged endurance.

As regional naval competition intensifies, Hai Kun SS-711 embodies Taiwan’s determination to reshape its maritime defense architecture. By combining indigenous industrial capability with discreet international technological support, Taipei is transitioning from symbolic submarine aspirations to tangible undersea combat power. The sixth sea trial off Kaohsiung signals that this transformation is no longer theoretical but is underway operationally, altering the deterrence calculus in one of the world’s most strategically sensitive maritime corridors.

Written by Alain Servaes – Chief Editor, Army Recognition Group
Alain Servaes is a former infantry non-commissioned officer and the founder of Army Recognition. With over 20 years in defense journalism, he provides expert analysis on military equipment, NATO operations, and the global defense industry.