Chinese S26T Submarine
Thailand has confirmed that it will move forward with the long-delayed acquisition of a Chinese-built S26T submarine, putting an end to years of uncertainty surrounding the project. After prolonged hesitation caused by engine supply issues, Bangkok has now approved contract amendments that allow construction to resume, signalling its commitment to closer defence cooperation with Beijing.
The Stalled S26T Submarine Programme
Thailand signed a deal on 5 May 2017 for one Chinese-built S26T submarine from CSOC. Bangkok initially aimed to buy three submarines. Budget limits forced the government to reduce the order to just one.
The keel was laid on 5 September 2019 at Wuchang Shipbuilding Industry Group’s facility in Wuhan, China. Soon after, the project hit difficulties that stalled progress and created uncertainty around its future.
Germany refused to supply MTU 396 diesel engines, which the Thai government had required for the 2,600-tonne submarine. In response, China offered CHD620V16H6 engines as replacements, but Bangkok doubted their long-term quality and reliability. Concerns about performance pushed the programme into limbo, with work effectively halted since 2021.
Chinese Engines Put to the Test
To reassure its partner, China subjected the CHD620 engines to more than 6,000 hours of bench testing. The Royal Thai Navy (RTN) reviewed the results and concluded that the engines demonstrated “quality comparable to the original” German systems and met the contractual performance limits. This verdict finally unlocked progress on the Chinese-built S26T submarine, with Thailand’s Cabinet approving the amended contract on 5 August 2025.
Compensation and Support Package
Bangkok negotiated additional benefits as part of the revised deal. China agreed to extend the warranty and maintenance support period from two to eight years, supply future equipment and weapons, and provide assistance with submarine simulators.
The compensation package is worth an estimated US$24.7 million. While the exact armaments remain unspecified, analysts expect the Chinese-built S26T submarine to be equipped with heavyweight torpedoes, sea mines, and possibly CM-708UNB anti-ship missiles.
At present, the submarine is about 64% complete. CSOC must now finish construction and deliver the boat by December 2028, a significant delay from the original 2023 delivery target. Thailand has already paid CSOC 7.7 billion baht (US$237 million) in 10 instalments, with 5.5 billion baht still outstanding.
Germany’s Block and Policy Shifts
The entire dispute stemmed from Berlin’s refusal to export the MTU engines, citing a European Union arms embargo imposed after the 1989 Tiananmen Square crackdown. While the embargo technically remains in force, European states have often applied it inconsistently. China, for example, still produces the Z-9 helicopter based on Airbus designs and has operated warships fitted with German-derived engines.
Defence analyst Siemon Wezeman of the Stockholm International Peace Research Institute SIPRI observed that Germany’s sudden decision was surprising, given its earlier tolerance. He suggested Berlin may now be applying stricter controls on dual-use exports to China’s military, or even objecting to Thailand as the end user, given its military-led government since the 2014 coup. Germany had already blocked Ukrainian BTR-3E armoured vehicles fitted with German engines from being delivered to Bangkok.
Broader Questions over China’s Submarine Engines
A key question is whether China’s Navy actually uses CHD620 engines on its Type 039 Yuan-class submarines. Because China tested them for Thailand, it seems likely its own fleet depends on alternative or foreign-derived engines.
Experts point out that China still produces German and French engines under old licensing deals, though details remain unclear. Meanwhile, Pakistan is building eight Hangor-class submarines in China and Karachi, fitted with the same CHD620V16H6 engines. Islamabad, along with other regional buyers, will closely monitor Thailand’s experience with these Chinese-built submarines.
Geopolitical Dimensions of the Submarine Deal
Beyond technical factors, choosing a Chinese-built S26T submarine highlights Thailand’s shifting strategic direction. Since the 2014 coup, relations with Washington have weakened, while ties with Beijing have grown stronger.
Scholar Dr Greg Raymond argues Thailand’s submarine purchase was driven by both capability needs and diplomatic pressure. He discovered evidence that the government pushed the navy towards Chinese submarines, despite stronger European and South Korean options.
By continuing with the deal, Thailand clearly signals a stronger tilt toward China in defence and politics. The submarine not only gives the Royal Thai Navy long-desired undersea capability but also deepens Bangkok’s reliance on Beijing.
