DEFENSE/Scholars analyze Taiwan's 'Narwhal' sub's X-shaped tail, sonar system

Taipei, Oct. 1 (CNA) Two Taiwanese defense scholars recently offered their insights into the design of Taiwan's first Indigenous Defense Submarine (IDS) after the "Narwhal" made its debut last week and was dubbed a milestone in Taiwan's efforts to produce domestic submarines and achieve "defense autonomy."

President Tsai Ing-wen (蔡英文) presided over the launch of the "Narwhal" on Thursday at a ceremony held in a shipyard in Kaohsiung belonging to CSBC Corp., Taiwan, the contractor for the IDS project.

Su Tzu-yun (蘇紫雲) and Shu Hsiao-huang (舒孝煌) from the government-funded think tank Institute for National Defense and Security Research (INDSR), who both attended the ceremony, told CNA over the weekend that they believe the prototype is primarily based on the body of Japan's Soryu-class submarines, while its sail, the superstructure that rises from the sub's deck, bears similarities to the United Kingdom's Astute class submarines.

According to CSBC Chairman Cheng Wen-lon (鄭文隆), the IDS prototype carries the pennant number "711" and features an X-shaped rudder, a departure from the cross-shaped rudder seen on previous models, giving it an edge over Taiwan's other submarines in active service.

Asked to comment, Su said that the Narwhal's X-shaped tail and its two horizontal stabilizers resemble the designs of the Israelis Dolphin class diesel-electric submarine.

The 'X' shape has proven to be more maneuverable than the traditional cruciform shape. The horizontal stabilizers, meanwhile, provide better stability, handling, stealth for the submarine, and allow for quicker emergency floats and dives when needed, Su explained to CNA.

At Thursday's ceremony, the bow of the submarine, along with the torpedo tubes and other critical components, were concealed beneath a Republic of China (Taiwan) flag.

Cheng informed reporters that day that this measure was taken to prevent the disclosure of many confidential parts of the submarine for security reasons, pending further testing.

Asked why the Navy chose to cover Narwhal's tail during the ceremony, Shu told CNA that "enemy forces" could estimate the prototype's underwater speed and acoustic fingerprints by observing the number of its propellers, their angles, and structural designs.

That is why most countries also cover the propellers of their new submarines during launching ceremonies, he added.

Besides its weapon system and propeller designs, both Su and Shu emphasized the importance of closely monitoring the indigenous submarine's sonar system, which was also concealed for security reasons.

According to both scholars, modern submarines, including the Narwhal, have a bow array sonar as the main sonar sensor, and a passive "incept sonar" system to detect sound waves approaching it.

The Narwhal also boasts a flank sonar array mounted symmetrically on the port and starboard sides of the submarine, enhancing detection characteristics at low frequencies thanks to the increased array aperture.

The flank sonar array provides the submarine with "eyes on its two sides," significantly expanding its range capabilities and performance, Shu added.

Meanwhile, Su noted his understanding of why the designers of the IDS prototype opted for the traditional Deep-Cycle Flooded/Wet Lead-Acid Battery over the more advanced Air-independent propulsion (AIP) system, a marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen.

Though the Wet Lead-Acid Battery has a shorter lifespan, it is more stable and reliable to operate, which is a priority for Taiwan's first IDS, he said.

According to retired Admiral Huang Shu-kuang (黃曙光), convener of the IDS program, following the ceremony, the prototype will undergo a harbor acceptance test on Oct. 1, followed by a sea acceptance test, and is expected to be delivered to the Navy before the end of 2024.

The IDS program also aims to build another submarine by 2027.

The construction of domestic submarines means Taiwan's Navy will have a total of three combat-ready submarines by 2025 and four by 2027, as well two existing Chien Lung-class (Sword Dragon) submarines purchased from the Netherlands in the 1980s.

Taiwan also possesses two World War II vintage submarines purchased from the United States in the 1970s, but they are now used exclusively for training purposes.