As Taiwan's first domestically built submarine, Hai Kun (海鯤號), moves through sea acceptance trials, attention is fixed not only on the vessel itself but on the small, insular force that will operate it.
At the center is the Republic of China Navy's 256th Squadron — Taiwan's only submarine unit, and one of its most opaque military communities. If Hai Kun is meant to symbolize renewal, the 256th represents both continuity and fragility: a highly trained cadre sustaining an aging fleet under mounting strategic pressure.
A Force Apart
Submariners in the 256th have a reputation within the Navy for being quiet, even aloof — and unmistakably proud. The image is not entirely accidental. Entry into the submarine force is competitive, the technical demands are relentless, and mistakes underwater are unforgiving.
Unlike surface combatants, which can be dispatched on short notice, submarine patrols are typically scheduled well in advance. That predictability, combined with relatively strong compensation and the force's elite status, has encouraged unusually long careers below the surface.
The result is something rarely seen elsewhere: what insiders call "golden sergeants" — senior non-commissioned officers who have served aboard submarines for two decades or more without transferring to the surface fleet. Their expertise is not merely procedural but instinctive. A slight change in the pitch of a mechanical hum can alert them to a fault before diagnostics do. In a force as small as Taiwan's, that kind of accumulated knowledge is not a luxury. It is ballast.
An Aging Backbone
Taiwan operates four submarines, but only two carry operational weight.
The Navy's two Guppy-converted Tench-class boats — Hai Shih and Hai Pao— are more than 60 years old and have effectively been relegated to training roles. The burden of deterrence falls on the two Dutch-built Zwaardvis-class submarines, Hai Lung and Hai Hu, commissioned in 1987 and now 38 years into service — well past the typical full-life cycle of a modern diesel-electric submarine.
Facing obsolescent components and a vanishing supply chain, the Navy launched a multi-pronged upgrade program covering electronic warfare, long-range heavyweight torpedoes, systems integration, and combat management architecture. The combat system refit alone — conducted by Taiwan's National Chung-Shan Institute of Science and Technology in cooperation with foreign contractors — carries a budget of NT$7.41 billion (approximately US$230 million), running from 2018 through 2027. Hai Lung has completed its overhaul; Hai Hu remains under the wrench.
These upgrades are designed to stretch viability, not perform miracles. Against the rapidly modernizing submarine and anti-submarine capabilities of the People's Liberation Army Navy, the margin for error is narrowing.
Training in the Shadows
Operational readiness follows a graduated structure. After individual certification and crew integration, submarines move into adversarial exercises divided into levels of complexity. At Level 1, the submarine maintains a fixed course, speed, and depth while surface ships attempt to locate it — essentially a controlled target. Level 2 permits limited maneuvering. At Level 4, the submarine conducts what the Navy calls a "sea kill": a fully autonomous, free-navigation exercise against surface forces, with only periodic reporting back to squadron headquarters.
In earlier decades, knowledge of a submarine's position was tightly restricted — the commander-in-chief, fleet commander, squadron commander, and a handful of staff officers were the only people in the entire Navy who knew where a boat actually was. Modern command-and-control systems now provide broader situational awareness, but precise real-time tracking remains limited.
That ambiguity occasionally became a training tool. A commander might order an unannounced sea kill on impulse — radioing a surface ship without prior notice and directing it to investigate a suspected contact: *"Urgent unscheduled drill. Suspected submarine bearing [X] off Green Island. Proceed to investigate."* The surface crew had no warning. Nor did the submarine. Both sides were forced into a genuine hunt.
In a second variant, the submarine would be instructed to surface briefly each hour, activate its radar for two full rotations — deliberately advertising its position — then dive. The aim was to give surface forces a real-time detection opportunity with no advance notice.
Such exercises have grown rare. Aging hulls tolerate fewer surprises.
Encounters Below the Surface
For patrol missions, submarines are assigned a defined geographic block and tasked with compiling hydrographic data: water conditions, depth profiles, and seabed characteristics — information foundational for wartime operations in surrounding seas.
Direct contact with adversary submarines, however, has never occurred in the literal sense, according to retired officers from the submarine community. Even during the 1996 Taiwan Strait crisis, there was no confirmed visual encounter. "Direct contact" in submarine terms means eyes on the target; everything else is acoustic inference.
Underwater interaction resembles *The Hunt for Red October* more than a gunnery duel. Sonar detections establish presence. The submarine with superior sensors typically detects first. When two boats approach a range where mutual detection is assumed, one side may deliberately generate noise — an underwater signal of awareness, analogous to the "Crazy Ivan" maneuver in the film: *I know you're there. You should know I know.*
Nationality cannot be determined through sonar alone. American, Japanese, Australian — acoustic signatures don't carry flags. In practice, Taiwanese submariners say, it was almost always the other side that signaled first. Not because of superior crews, but because of superior equipment. The message, regardless of who sent it: You are near our operating space. Do not come closer.
Testing the Limits
One extended-range endurance test took a Zwaardvis-class submarine to the vicinity of the Mariana Trench — the deepest point on Earth. The mission examined diesel charging cycles and fuel consumption at extreme distance. Fuel, the crew found, was not the limiting factor. Human endurance was.
The deployment also tested sonar and communications range at the outer edge of the fleet's reach. With a rated effective sonar depth measurement of 6,000 meters, the system simply stopped registering bottom returns near the trench. The ocean floor was beyond its reach.
A Narrowing Window
Against this backdrop, *Hai Kun* carries weight beyond its hull. The Tench-class boats are functionally relics. The Zwaardvis-class has been upgraded but is aging into strategic uncertainty. Few in uniform are publicly willing to assess how the current fleet would fare against modern Chinese anti-submarine warfare capabilities. Privately, many acknowledge that the margin is thin.
For Taiwan — an island whose defense doctrine hinges on denying sea control to a larger adversary — submarines remain one of the few platforms capable of asymmetric leverage. They complicate planning, impose caution, and stretch an opponent's resources.
Whether *Hai Kun* meets operational expectations will shape not only the future of Taiwan's indigenous submarine program, but the survival of the tight-knit 256th Squadron that must carry it forward. If the new hull succeeds, it extends the force's relevance. If it falters, Taiwan risks losing more than a platform — it risks losing a culture of expertise that took decades to build, and cannot be rebuilt overnight.
