CaliToday (19/9/2025): After a saga of delays and controversy spanning several years, the Royal Thai Navy has officially finalized a contract with China to procure one S26T Yuan-class diesel-electric attack submarine. The signing marks a pivotal moment in a deal that has been plagued by political debate and significant technical hurdles, particularly concerning the vessel's propulsion system.
The agreement, valued at approximately 13.5 billion baht (around $369 million), brings to a close a period of intense negotiation and uncertainty. The original deal, approved by the Thai government in 2017, was for three submarines but was later scaled back to a single vessel amid public scrutiny and the economic impact of the COVID-19 pandemic.
The primary obstacle that stalled the project for years was an engine embargo. The submarine was originally designed to be equipped with state-of-the-art MTU396 diesel engines from Germany. However, due to a European Union arms embargo imposed on China, Germany refused to authorize the sale of the engines to the Chinese shipyard, China Shipbuilding & Offshore International Co. (CSOC), for installation in a military vessel destined for a third country.
This created a diplomatic and technical impasse that threatened to derail the entire procurement. After extensive back-and-forth negotiations, Thai and Chinese officials reached a compromise earlier this year. The solution involves substituting the German engine with a Chinese-made CHD620 marine diesel engine. The Royal Thai Navy reportedly dispatched technical teams to China to inspect and approve the performance and safety standards of the domestically produced engine before giving the final green light.
The S26T Yuan-class is an export variant of the Type 039A submarine used by China's People's Liberation Army Navy. It is a modern diesel-electric attack submarine equipped with an Air-Independent Propulsion (AIP) system, which allows it to operate submerged for extended periods, significantly enhancing its stealth and operational endurance. The submarine will be armed with a variety of torpedoes and anti-ship missiles, representing a substantial leap in undersea warfare capability for the Royal Thai Navy, which has not operated a submarine fleet for over 70 years.
The finalization of the deal is seen as a significant geopolitical development, underscoring the deepening defense and political ties between Bangkok and Beijing. For China, it marks a key success in its military export ambitions in the strategically important Southeast Asian region. For Thailand, the acquisition is framed as a critical step in modernizing its navy and protecting its maritime interests in the Gulf of Thailand and the broader Andaman Sea.
The submarine is currently under construction in Wuhan, China, and its delivery is now expected to proceed under the revised terms of the agreement.
