The Indigenous Defence Submarine (IDS) programme, seen as a centrepiece of the island’s efforts to strengthen its asymmetric naval capabilities, is facing its biggest test yet.

Sea tests for the prototype vessel began earlier this year but fell behind schedule, raising questions over whether Taiwan’s most ambitious defence project in decades could meet its targets.

According to the navy, the Hai Kun was scheduled to undergo four to five surface navigation tests, followed by a shallow dive trial at 50 metres (164 feet) and a deep dive trial at 200 metres.

The first surface test was conducted in mid-June, but after the third surface test on July 3, the submarine spent weeks in dry dock before returning to the pier in Kaohsiung port on September 2, a span much longer than had been anticipated for post-trial maintenance.