Defence in brief: Taiwan’s Hai Kun submarine enters trials

Taiwan’s first domestically built Hai Kun submarine has started its final harbour trials, according to a 17th June post made on Facebook by the Kaohsiung Good Day Association, a civic organisation supporting the city of Kaohsiung in southern Taiwan. An image posted by the account shows the submarine moving through one of the ports in the city.

It appears from other reporting that the Hai Kun submarine set out on its harbour trials on Saturday the 14th June, and the timestamped image posted by the Kaohsiung Good Day Association shows the 17th June. This indicates that the submarine has conducted at least three days of trials around the harbour. 

The tests included propulsion, the power system, and buoyancy, with the next set of trials expected to cover the boat’s ability to dive. The Hai Kun submarine has been built by the CSBC Corporation, which builds and repairs commercial vessels. CSBC also built Taiwan’s Cheng Kung class frigates, of which there are eight, as well as numerous other military ships for the country’s government. 

The Hai Kun submarine was last seen leaving its CSBC port in April, towed by a support boat, according to Focus Taiwan. However, the latest tests were conducted under the submarine’s own power, indicating that it is progressing through its build, albeit behind schedule. The Sea Acceptance Tests, which will follow harbour acceptance, were expected to start in April ahead of entry into service in November.

Calibre comment

The project was initiated in 2014 under the programme name Indigenous Defense Submarine and a contract awarded to CSBC in 2018 for a total of eight boats. There have been numerous delays and Taiwan has had to scour the international market for expertise, both to advise its navy and help with construction. This is a reflection of the complexity involved in building submarines. 

By Sam Cranny-Evans, published on 17th June, 2025. The featured image shows the Hai Kun submarine at its unveiling ceremony. Credit: By 總統府 – https://www.flickr.com/photos/presidentialoffice/53219332200/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=138219002