Taiwan's first domestically built submarine is nearing the end of its testing programme, a positive sign for the island's naval build-up and its defence industry.

• The Hai Kun went out for its 25th sea trial and 19th dive test, with the programme now in its final testing stretch.
• Remaining tests get harder — deeper dives and longer time submerged.
• Most of the system integration problems that dogged earlier trials have been fixed after repeated tuning and help from the original equipment makers.
• Military analysts frame the project as essential, arguing a navy without submarines is only half a navy.
• Public interest is high, with military enthusiasts gathering at the Kaohsiung dockside before dawn to watch the boat sail.

Outlook: If the deeper and longer dives go well, the submarine should finish trials and move toward delivery to Taiwan's navy.