By Hsiao-Huang Shu

Taiwan’s first domestically built submarine was named “Haikun” ( 海 鯤 ) during a completion and naming ceremony at the state-run CSBC Corporation Taiwan ( 台灣國際造船公司 ) on September 28, 2023. President Tsai personally hosted the ceremony. The name “Haikun,” meaning Narwhal, is derived from the Chinese classic Zhuangzi ( 莊子 ).[1] Narwhal embodies the qualities of vastness and elusiveness. The choice of the name Haikun for the submarine signifies the expectation that it will operate adeptly in a stealthy manner, navigate the deep-sea environment, and be hard to detect. This article aims to analyze the implications of Haikun and broaderly indigenous defense submarine (IDS) project for Taiwan.

First of all, submarines have emerged as the primary assets in modern naval warfare, particularly for smaller states like Taiwan. They play a pivotal role in safeguarding maritime interests by thwarting potential enemy invasion. Given Taiwan’s strategic island location, maintaining maritime transportation routes for the import of energy and food is crucial for wartime resilience.

In the event of a blockade by the People’s Liberation Army (PLA) Navy, Taiwan can leverage its submarines to counteract the blockade. This involves ensuring the safety of waterways, protecting the Navy’s surface ships, and preventing PLA Navy submarines from posing a threat to our surface vessels. Effectively countering the operations of PLA Navy surface ships will also be within the capabilities of Taiwan’s Navy, showcasing the versatility and value of submarines in maritime defense strategies.

China’s persistent gray zone harassment, including the near-daily deployment of warships in Taiwan's vicinity, poses a significant threat to Taiwan's maritime security. To counter this threat, the Taiwanese Navy has dispatched ships to monitor and deter Chinese incursions. However, China may increasingly employ submarines for these activities. A robust Taiwanese submarine fleet could effectively patrol surrounding waters, detect underwater threats, and exert pressure on the PLA Navy's surface ship deployments.[2]

Generally speaking, the tasks Taiwan’s submarines are expected to take on in the future include:

1. Deployed in underwater ambush areas in key sea lanes or combat areas to attack the PLA Navy’s surface combat forces.

2. Protecting the operational safety of the Navy’s surface ships and avoiding threats from PLA Navy submarines.

3. Deployed to ambush the PLA Navy’s surface combat ships: waiting for opportunities to attack important targets (such as aircraft carriers, large landing ships, and supply ships) on the PLA Navy’s ship routes or in combat deployment areas; launching joint antisubmarine operations with Taiwan’s Air Force and Navy.

4. Performing underwater patrol missions, cooperating with air and surface anti-submarine ships, detecting the activities of PLA Navy submarines, and strengthening joint anti-submarine warfare capabilities.

5. Carrying out intelligence surveillance and reconnaissance missions in critical areas.

6. Carrying out special operations or mine-laying missions.

The PLA Navy’s submarine force’s capability is growing rapidly. In addition to traditional diesel-electric submarines, the number of nuclear-powered attack submarines and strategic missile submarines is also gradually increasing, posing a major threat to the United States, Australia, India and other neighboring countries. Due to this challenge, Taiwan must strengthen its underwater combat capabilities. It needs to improve the monitoring capabilities with regard to the PLA Navy’s underwater activities, and cooperate with neighboring countries to strengthen comprehensive monitoring of PLA Navy submarines in the Western Pacific.

The type and design of the submarine Haikun were mainly completed by Taiwan domestically. The Navy found the best configuration through ship model testing. Haikun is similar to the diesel-electric submarine design of the world’s advanced countries, such as the German Type 212 and the Japanese Soryu class.

It is a fact that Taiwan has no experience in building submarines in the past. To develop from scratch, many difficult problems, including the cost, construction cycle and risks, had to be tackled. In order to reduce technical risks and shorten the research and development cycle, the construction team followed the existing submarine type with assistance from international allies who provided design and construction guidance and various support. These factors helped make the building of the submarine successful.

The submarine Haikun adopts a composite hull design. The middle section is a single hull, a pressure hull. The front and rear sections are double hulls. The pressure hull is the inner layer, and the outer hull does not bear water pressure. At the same time, because the outer hull is relatively small and thin, the most appropriate hull shape could be identified based on ship model testing to facilitate stealth and underwater navigation.

The pressure hull is one of many key technologies for submarine building. The pressure hull must be able to maintain a true round cross-section configuration to ensure resistance to underwater pressure. At the same time, welding process requirements are extremely demanding. In addition to pre-heating, the welding position also needs to be checked by X-ray to ensure there are no micro-cracks. Without the ability to fabricate and weld the pressure hull, it would be impossible to build an advanced submarine.

Currently, Taiwan’s China Steel Corporation (CSC) is able to produce HSLA80 steel plates. They were produced experimentally in 2019 and the welding technology verified. Non-breakage tests were conducted in 900-meter-deep sea off Taiwan’s east coast and underwater blast tests carried out, and these tests were passed.[3]

The HSLA80 steel plate can reach a tension of 550MPa, which is higher than the 350MPa tension of the Swordfish-class FE510 steel plate. The Haikun class’s diving depth may reach about 300-400 meters, and its performance will be better than the Swordfish-class submarine.

Haikun’s special design includes propeller and tail rudder. Many parts of the hull of this submarine were “wrapped” at the ceremony, including the bow of the ship covered with a curtain decorated with the national emblem of blue sky and white sun, the sonar array on the side, and the propeller on the stern of the ship. This was for reasons of secrecy.

The X-type tail rudder design features four rudder surfaces that can be controlled independently. All four rudder surfaces can play a combined role in horizontal or pitching movements, making underwater maneuverability better. If one rudder surface is damaged, the other rudder surfaces can also be accepted. Control is complicated and requires a computer. There are also two horizontal stabilizer surfaces, which may increase the submarine's operational performance.[4]

Haikun is equipped with 7 sonars. The high-frequency sonar above the bow is used for precise positioning, determining underwater navigation obstacles, and ensuring navigation safety. The active/passive sonar under the bow is used to emit sound waves and detect echoes. It can also passively listen to other sound sources and detect underwater objects. Another three sets of low-frequency passive sonar are installed on the side to locate targets at longer distances. They can also be used for underwater listening to increase detection capabilities.[5]

The difficulty in Taiwan’s production of submarines lies in “red zone” equipment, which refers to equipment or technologies that Taiwan cannot develop and for which it must seek assistance from outside. This includes combat systems, sonar, power systems such as diesel main engines, generators and motors, and weapon systems, such as torpedoes or submarine-launched missile systems. In addition, although the “yellow zone” equipment is difficult to obtain, Taiwanese companies should have the ability to make such products in the future; the “green zone” refers to equipment that can be produced in Taiwan.

Most of the combat systems come from specialized manufacturers from various countries. Due to fear of interference by China, Taiwan keeps the source of its equipment highly confidential. It is because of the assistance of friendly countries that the nation's submarine manufacturing was successful.

The main weapons of submarines include torpedoes, missiles, mines, etc. Haikun is expected to be equipped with US-made MK48 heavy-duty torpedoes and should also be equipped with submarine-launched Harpoon missiles.

Other sensing systems include an advanced integrated periscope system that integrates visible light, near infrared (SWIR), medium wave thermal imaging (MWIR), and low-light, as well as electronic warfare system antennas, direction finding antennas and GPS Receiving antennas that can reduce the number of antennas and help strengthen shielding.[6]

Taiwan’s Navy pays attention to the quietness of this submarine. In addition to using large 7-piece scimitar blades, it can reduce the speed of the blades to reduce the source of noise.[7] The main engine and other machinery are equipped with shock-absorbing seats to reduce vibration and noise. The streamlines of the hull and the surface treatment of the hull also pay attention to reducing noise. Currently, the hull does not have silencer tiles installed. If the construction technology matures in the future, it is not ruled out that they can be added.

The submarine Haikun is the Taiwan’s first domestically built submarine, though it’s a still prototype. Taiwan’s Navy expects to conduct static tests in 2024, and then conduct sea trials to verify various systems and correct deficiencies. Ideally, if the construction of 8 submarines is successfully completed, the Taiwanese navy will significantly enhance its combat capabilities, and will be able to effectively resist PLA Navy’s maritime threats.