Taiwan’s First Indigenous Submarine ‘Hai Kun’ Completes First Sea Trial

Taiwan has taken a major step forward in strengthening its maritime defense capabilities. On June 17, 2025, the country’s first Indigenous Defense Submarine (IDS), named Hai Kun (SS-711) — also known as Narwhal — successfully completed its maiden sea trial, according to its builder CSBC Corporation. This achievement marks a historic milestone for Taiwan, as it builds its own submarine for the first time in modern history.

A Major Moment at Sea

The Hai Kun was spotted operating independently in the Port of Kaohsiung last week. On its first trial day, the submarine sailed out of the CSBC shipyard, passed Cijin Island (旗津), and was observed with over a dozen military personnel and technicians aboard, some standing on its deck and sail.

To secure the submarine during these sensitive sea trials, Taiwan’s Navy deployed a wide range of naval and aerial assets including assault boats, missile boats, frigates, and aircraft. This was done to protect the submarine’s position, route, and technical details from potential surveillance or sabotage, especially amid ongoing tensions in the Taiwan Strait.

Sea Trial Phases and Submarine Capabilities

CSBC Corporation revealed that Hai Kun underwent multiple systems tests during the trial, including propulsion, steering, electrical systems, ventilation, communication, and navigation checks. The sea trials are planned in three stages:

1. Surface Navigation Tests

2. Shallow-Depth Testing

3. Progressive Deep-Diving Tests

After each stage, the submarine’s systems will be reviewed, and adjustments made based on performance and safety standards before moving to the next phase.

Amid online speculation about a visible bulge on the submarine’s bow during trials, CSBC clarified that it is not a structural flaw, but actually the housing for the submarine’s passive ranging sonar system — a critical feature for underwater detection and navigation.

CSBC urged the public to support the program, emphasizing the national pride associated with Taiwan’s growing defense self-reliance.

Challenges Ahead

Despite Hai Kun’s successful trial, the IDS program faces political hurdles. Around 50% of the budget for additional indigenous submarines remains frozen, largely due to opposition parties seen as having pro-China leanings. These funds will only be released after Hai Kun completes its Sea Acceptance Test and a comprehensive report is submitted to the Taiwanese legislature.

However, Navy Chief of Staff Vice Admiral Chiu Chun-jung confirmed that the submarine is still on track for delivery in November 2025, as originally scheduled.

Taiwan’s Existing Submarine Fleet

Currently, Taiwan’s Republic of China (ROC) Navy operates four submarines:

• ROCS Hai Shih (Sea Lion) SS-791 and ROCS Hai Pao (Seal) SS-792:
  These are former World War II-era U.S. Navy submarines, transferred in the 1970s and upgraded under the GUPPY program. Remarkably, they remain operational.

• ROCS Hai Lung (Sea Dragon) SS-793 and ROCS Hai Hu (Sea Tiger) SS-794:
  These are Chien Lung-class submarines, built by the Netherlands in the 1980s. Both submarines are armed with AEG SUT 264 torpedoes, Harpoon anti-ship missiles, and MK-48 torpedoes acquired from the U.S.

With the impending induction of Hai Kun, Taiwan’s submarine fleet will gain a modern, locally built vessel with advanced stealth and combat capabilities — a critical asset amid the island's growing security challenges.

The successful maiden trial of the Hai Kun submarine is more than a technical achievement — it’s a strategic message of resilience and self-reliance. As Taiwan faces increased military pressure in the region, building its own defense platforms like Hai Kun signals a determined commitment to safeguarding its maritime sovereignty.