TAIPEI : Taiwan has entered a critical new phase in its long-running indigenous submarine program with the first successful dive tests of Hai Kun (SS-711), the island’s first domestically built submarine, a milestone that defense officials say significantly advances Taiwan’s undersea deterrence capability.
According to Taiwan’s Liberty Times and other local media, Hai Kun conducted its initial controlled submersion on Sunday, marking the first time the vessel has operated underwater since construction was completed. The test follows more than a year of surface, harbor, and floating trials, and formally transitions the program from basic seaworthiness checks to full underwater performance evaluation.
The submarine is the flagship platform of Taiwan’s Indigenous Defense Submarine (IDS) program, a strategically sensitive effort aimed at countering growing military pressure from China and reducing long-standing dependence on foreign-built naval platforms. Built by CSBC Corporation at Kaohsiung, Hai Kun was launched in early 2024 and began land-based and harbor testing at Kaohsiung port in July 2024.
Technical Hurdles and Recovery
Progress toward the dive phase was not without setbacks. In September 2024, Taiwanese media reported that Hai Kun suffered a main engine failure during sea trials, traced to a rupture in internal piping systems. The incident forced a temporary suspension of testing and prompted extensive inspections and repairs.
After corrective work was completed, the submarine resumed trials in mid-2025. Departure tests were conducted in June, followed by floating and stability trials completed in November. Defense officials described these stages as essential prerequisites for underwater operations, ensuring hull integrity, ballast control, and system safety before submersion.
The January dive test now opens a new sequence of underwater evaluations that will gradually expand the submarine’s operating envelope, including tests at increasing depths and under different sea conditions. These trials are designed to assess propulsion reliability, acoustic performance, sensor integration, and overall survivability.
Delayed Timeline, Unresolved Sensitivities
Taiwan’s Ministry of National Defense has set June 2026 as the target date for Hai Kun’s formal handover to the navy, approximately seven months later than originally planned. Officials attribute the delay primarily to problems with the submarine’s integrated platform management system, which initially failed to properly interface with other onboard sensors and subsystems.
Sources cited by Taiwanese media said the issue was eventually resolved with assistance from foreign engineers, allowing signal connectivity between the submarine’s systems to function normally. The ministry has declined to identify the foreign specialists involved, reflecting the political sensitivity surrounding international cooperation on submarine technology.
Despite the delay, defense officials emphasized that no major structural flaws were identified and that the revised schedule reflects caution rather than fundamental design failure.
Strategic Significance
Hai Kun is the lead boat of a planned class of eight indigenous submarines that Taiwan aims to build and deploy by 2027. Once operational, the class is expected to form the backbone of Taiwan’s undersea warfare capability, providing a stealthy, survivable force designed to complicate Chinese naval operations in the Taiwan Strait and surrounding waters.
Analysts note that submarines play a disproportionate role in Taiwan’s defense planning, offering one of the few credible means to threaten larger adversary fleets while operating in a highly contested environment. The IDS program is therefore viewed as a cornerstone of Taiwan’s broader shift toward asymmetric defense capabilities.
The commencement of dive testing places Hai Kun among the most closely watched naval programs in East Asia, as Taiwan accelerates domestic defense production amid mounting regional tensions. If remaining trials proceed as planned, officials say the submarine could enter limited operational service shortly after delivery, marking a historic milestone for Taiwan’s defense industry and its navy.
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