Taiwan starts propulsion tests of first indigenous Hai Kun submarine.

As reported by UDN on June 14, 2025, Taiwan’s first domestically built submarine, the Hai Kun (SS-711), began autonomous movement under its own power within the Port of Kaohsiung. This represents the vessel’s transition from dockside integration and harbor acceptance testing to the initial dynamic phase of pre-sea trials. Since its launch on September 28, 2023, by CSBC Corporation at its purpose-built facility in Kaohsiung, the submarine has remained moored while undergoing system calibration and mechanical verification.
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The Hai Kun (SS-711) has an estimated submerged displacement ranging from 2,500 to 3,000 tons and a length between 70 and 80 meters, although no official figures have been confirmed. (Picture source: Facebook/IDF 經國號)

The Hai Kun's recent movement inside the harbor without tug assistance indicates successful activation of the diesel-electric propulsion system and associated control systems. The vessel is the first of up to eight planned under the Republic of China Navy’s Indigenous Defense Submarine (IDS) program, a strategic project aimed at reinforcing Taiwan’s capacity to conduct undersea operations in deep waters east of the island.

The Hai Kun (SS-711) has an estimated submerged displacement ranging from 2,500 to 3,000 tons and a length between 70 and 80 meters, although no official figures have been confirmed. The submarine uses a conventional diesel-electric propulsion configuration, likely consisting of multiple diesel-generator sets to charge high-capacity batteries that power a single electric motor connected to a shaft-based propulsion system. The hull design features a teardrop form and is equipped with an X-shaped rudder arrangement to improve submerged maneuverability. Technical analysis indicates that the vessel’s configuration draws heavily from the Dutch Zwaardvis-class, which served as the design basis for the Hai Lung-class submarines acquired from the Netherlands in the late 1980s. The Hai Kun’s construction involved the integration of multiple subsystems, combining domestically produced components with foreign-sourced technologies, including sonar arrays, periscopes, optronic masts, and command and navigation systems.

Taiwan’s development of the Hai Kun-class, also known as the Indigenous Defense Submarine (IDS) program, was initiated following repeated failures to procure new platforms from foreign governments due to export restrictions and geopolitical pressure, particularly from the People’s Republic of China. By the mid-2010s, Taiwan formalized a national plan to build its own submarines. The Ministry of National Defense assigned CSBC Corporation the responsibility for hull construction and assigned system integration and oversight to the National Chung-Shan Institute of Science and Technology (NCSIST). International technical advisors were reportedly involved in the early stages, contributing to acoustic modeling, propulsion layout, and electronic system design. The Hai Kun is believed to include six 533 mm torpedo tubes compatible with heavyweight torpedoes such as the Mk 48 Mod 6. While no torpedo test launches have yet been reported, future phases of testing are expected to address combat system validation and live-fire trials. The submarine’s sensor suite likely includes bow-mounted sonar, flank array sonar, and electronic support measures for detection and tracking functions.

After its launch in September 2023, the Hai Kun underwent a harbor testing phase lasting approximately nine months. During this period, shipyard teams and naval engineers conducted evaluations of electrical systems, fluid transfer systems, trim and ballast controls, command consoles, battery cycling, and propulsion activation procedures. Movement within the harbor in June 2025 confirmed that propulsion, helm controls, and onboard navigation systems are functioning in coordination. The next steps involve open-sea testing in designated offshore test zones east of Taiwan. These sea trials will include assessments of submerged propulsion, battery performance, hull integrity under pressure, sonar effectiveness, periscope and optronic mast visibility, and internal system integration under full operational loads. Testing in live maritime conditions will also allow engineers to measure acoustic signature levels and evaluate the reliability of combat management interfaces in navigation and surveillance scenarios.

The expected test area includes the waters east of Taiwan and the Bashi Channel, where sufficient ocean depth and maritime security conditions allow for submerged trial operations without civilian interference. These areas could be considered more suitable for submarine activity than the Taiwan Strait, which is shallow, narrow, and heavily trafficked. According to available information, Taiwan’s strategic planning anticipates that the IDS fleet will operate primarily in these deeper Pacific-facing waters, where submarines can perform surveillance, monitor maritime activity, and contribute to early-warning functions. The Bashi Channel connects the South China Sea to the Philippine Sea and is a key passage in the first island chain. The Taiwan Navy (ROCN) doctrine calls for a layered defense strategy supported by undersea assets capable of denying access or detecting hostile naval movements. The Hai Kun’s submerged endurance, acoustic quieting features, and electronic warfare capabilities are designed to support such operations by enhancing situational awareness in forward maritime zones.

As of June 2025, the Hai Kun remains at the CSBC dock in Kaohsiung, where final system verifications, crew training, and operational checks are ongoing ahead of open-ocean deployment. The ROCN expects the vessel to reach initial operational capability between late 2025 and early 2026, depending on the progress and outcome of sea trials. A second IDS-class submarine is already under construction at the same facility, incorporating lessons learned during Hai Kun’s assembly and testing. The IDS program plans for a total of eight units, with construction paced according to available funding, technological readiness, and delivery timelines. The Republic of China Navy’s current submarine fleet includes two Hai Lung-class vessels and two older Hai Shih-class submarines originally built in the 1940s as part of the US Navy’s Tench-class. The latter are no longer considered combat-capable and are largely retained for secondary roles. The Hai Kun and its successors are intended to gradually replace these platforms and provide Taiwan with a modern, indigenous undersea deterrent.

The Indigenous Defense Submarine program reflects Taiwan’s shift toward self-reliance in naval manufacturing and aims to restore a consistent submarine patrol capability around the island’s eastern periphery. The Hai Kun’s propulsion test and harbor navigation phase confirm progress toward that objective. Once deployed, the IDS-class will enhance Taiwan’s ability to monitor undersea approaches, perform intelligence and surveillance missions, and conduct limited interdiction operations within its area of responsibility. The integration of foreign subsystems with domestic shipbuilding allows Taiwan to continue developing naval technologies without relying on external submarine exports. As the first unit of its class, the Hai Kun will also serve as a reference platform for improvements in subsequent boats. Operational success during sea trials will determine the degree to which the IDS fleet can meet the Taiwan Navy’s long-term goal of fielding a credible and persistent submarine force within the strategic context of the Western Pacific and the first island chain.