Taiwan Navy Begins Dive Tests of Hai Kun First Indigenous Attack Submarine.

Taiwan’s Republic of China Navy, on January 26, 2026, began the first controlled dive tests of the Hai Kun submarine, hull number SS-711, departing Kaohsiung harbor for submerged operations. The milestone advances Taiwan’s Indigenous Defense Submarine program toward a planned mid-2026 delivery after overcoming earlier technical delays.

The Republic of China Navy has initiated the first controlled dive tests of its domestically built Hai Kun submarine, marking a critical transition from surface evaluations to underwater operations, according to reporting by Taiwan’s Liberty Times. The submarine, designated SS-711, departed Kaohsiung harbor on January 26 and entered a new phase of sea trials following months of harbor, floating, and surface testing conducted throughout 2025 under Taiwan’s Indigenous Defense Submarine program.
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The Hai Kun submarine finished its floating test on November 28, 2025, accompanied by the Endeavor Devil Fish unmanned surface vessel. (Picture source: CSBC Corporation)

Hai Kun’s entry into underwater testing unfolds under close public and institutional scrutiny. Built by CSBC Corporation, the submarine represents the first time Taiwan designs and constructs a modern attack submarine entirely on its own territory. Observers along the Kaohsiung waterfront note the presence of additional test personnel aboard during departure, a visible reminder of the cautious approach adopted for initial dives. The January trial confirms that the vessel has moved beyond static and surface evaluations into controlled submersion, a step that validates hull integrity, ballast systems, and core safety procedures before deeper and longer profiles are attempted.

The program’s timeline reflects the complexity of establishing a sovereign submarine capability. Hai Kun is launched in 2024 and begins land based testing at Kaohsiung port in July of that year. Sea trials, initially expected earlier, face interruptions. In September 2024, Taiwanese media report a main engine failure during trials, traced to a rupture in internal piping systems. Repairs follow, and the submarine resumes departure trials in June 2025 before completing floating tests in November. These setbacks, while costly in time, provide critical feedback for a shipyard and navy navigating unfamiliar technical ground.

Hai Kun is a conventionally powered diesel electric submarine designed for sustained operations in the shallow and acoustically complex waters surrounding Taiwan. Open source estimates place its submerged displacement in the 2500 to 3000 ton range, with a hull length of roughly 80 meters, though official figures remain undisclosed and should be treated cautiously. Propulsion relies on diesel generators charging battery banks, enabling silent electric running when submerged. This architecture favors acoustic discretion but imposes constraints on endurance, as periodic snorkeling is required to recharge batteries in the absence of a confirmed air independent propulsion system for the lead boat.

Sensor and systems integration remains central to the current test phase. Hai Kun reportedly carries an indigenous combat management system connected to a sonar suite that includes bow mounted arrays and flank sensors optimized for passive detection. One of the key causes of delay, cited by sources close to the program, involves difficulties linking the integrated platform management system with onboard sensors. According to Taiwanese media, these issues are resolved with assistance from foreign engineers, restoring stable signal connections across the submarine’s internal networks. The identities of these specialists are not disclosed, reflecting the political sensitivity surrounding external support.

Weapons integration is expected to follow progressively once submerged handling and safety envelopes are validated. Taiwanese officials have previously indicated that Hai Kun is designed to deploy heavyweight torpedoes for both anti submarine and anti surface warfare. While specific models are not confirmed publicly, such weapons typically offer engagement ranges measured in tens of kilometers and rely on wire guidance and active or passive homing in terminal phases. Their effective use depends as much on sensor performance and crew proficiency as on raw specifications, reinforcing the importance of the ongoing trials.

Hai Kun is tailored to exploit the geography of the Taiwan Strait and adjacent seas. Diesel electric submarines operating on battery power can achieve very low acoustic signatures, particularly in littoral waters saturated with background noise from commercial shipping. In such conditions, a single submarine can impose disproportionate demands on an adversary’s anti submarine forces, forcing surface combatants, helicopters, and maritime patrol aircraft to devote time and resources to detection and tracking. While endurance and speed are limited compared to nuclear powered submarines, careful mission planning allows Hai Kun to threaten sea lines of communication and high value naval units at critical moments.

Beyond the platform itself, the start of dive testing carries broader implications. Hai Kun is the lead boat of a planned class of eight indigenous submarines that Taiwan aims to build and deploy by 2027. For Taipei, the program is less about parity and more about survivability and uncertainty, reinforcing an undersea deterrent intended to complicate any hostile naval operation. Regionally, the trials are closely watched as an indicator of Taiwan’s ability to sustain advanced defense production under diplomatic pressure. As undersea capabilities continue to shape the military balance in East Asia, Hai Kun’s progression from surface trials to submerged testing adds a new layer to the strategic calculus surrounding security and stability in the Taiwan Strait.