Thailand, long treated in Washington as a reliable if sometimes awkward military partner, has just ordered a Chinese submarine, raising questions about where loyalties, leverage and security cooperation in Southeast Asia really stand.
Thailand’s discreet move that caught Washington’s eye
On 16 September 2025, in a government compound in Beijing, Thailand signed a deal to acquire a Chinese-built Type 039A submarine, known in export form as the S26T. On paper, it is a routine arms sale. Politically, it reads like a pointed message.
Thailand is not just another customer on China’s defence export list. The country is one of America’s oldest allies in Asia, a partner since the Cold War and a “major non-NATO ally” since 2003. US aircraft once flew from Thai bases during the Vietnam War. Joint exercises and security assistance have been staples of the relationship for decades.
Bangkok’s choice of a Chinese-built submarine does not overturn the alliance with Washington, but it signals that Thailand refuses to be locked into a single camp.
The path to this contract started in 2017, when Bangkok agreed to buy three submarines from China, a historic first for the Royal Thai Navy, which had gone without undersea capability for years. By 2019, the hull of the first boat was ready.
Then European sanctions collided with Asian ambitions. The design relied on German MTU diesel engines. Berlin refused export clearance because of the long-standing EU arms embargo on China that dates back to the Tiananmen Square crackdown. The programme stalled.
China responded by developing its own alternative powerplant. After years of testing and repeated assurances over reliability, Thailand accepted the locally produced engines. Budget pressures trimmed the initial order from three boats to just one, but the political signal remained intact. Delivery is currently planned for 2028.
What Thailand is actually buying
The S26T is not a Hollywood-style superweapon, yet it represents a serious upgrade for the Thai navy.
- Displacement: around 2,550 tonnes
- Length: roughly 77 metres
- Propulsion: diesel-electric with an air-independent propulsion (AIP) Stirling system
- Endurance: up to about 65 days at sea
The AIP system allows the submarine to stay submerged longer without surfacing or using a snorkel mast, which reduces the risk of detection. For coastal defence, sea-lane monitoring and basic deterrence, that endurance matters more than sheer size or firepower.
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For Thailand, the boat fills a capability gap and provides a training platform for crews that have not operated submarines for a generation. For China, it is a showcase: a proof that its shipyards can now export complex, long-endurance submarines to a US ally.
Strategic ambiguity as state policy
The Thai military regime that emerged from the 2014 coup triggered criticism in Washington and partial freezes in US security assistance. Leaders in Bangkok interpreted that as a warning about overdependence on the United States.
Since then, Thai diplomats and generals have methodically diversified partnerships. China offers arms with fewer conditions on domestic politics, lines of credit and high-level attention. Russia, South Korea and European suppliers have also courted Bangkok.
Thailand is practising what regional analysts call “hedging”: avoiding a clear choice between Washington and Beijing while extracting benefits from both.
That strategy is not unique. Across Southeast Asia, governments try to balance American security guarantees with Chinese trade and investment. Thailand’s submarine contract fits this pattern. It signals to Washington that Thailand has options, while indicating to Beijing that Bangkok is open to deeper cooperation, including in sensitive domains such as undersea warfare.
How Beijing uses steel as diplomacy
For China, the deal is not just about revenue for its shipyards. Beijing has spent two decades transforming itself from a net arms importer into a top-tier exporter. By some estimates, China now ranks fourth among global weapons suppliers, behind the US, Russia and France.
Warships have become central to that effort. Frigates, corvettes and submarines are sold with training packages, maintenance contracts and technology transfers that tie foreign navies to Chinese industry for years. Those relationships can later translate into diplomatic support on contested issues, from the South China Sea to Taiwan.
The Thai deal includes training for crews and a partial transfer of technology. That means Chinese engineers and advisers will likely spend extended periods in Thai shipyards and naval facilities, gaining insight into local procedures and building informal networks.
Does this change the military balance?
On a purely military level, the answer is modest. The Royal Thai Navy remains small next to the fleets of China, Japan, India, South Korea or the United States. A single diesel-electric submarine will not tilt the undersea balance in the wider Indo-Pacific.
The region’s main naval heavyweights continue to be:
- China’s rapidly expanding blue-water fleet
- Japan’s high-tech, quiet submarines and destroyers
- India’s mix of domestically built and imported boats
- US carrier strike groups and nuclear-powered submarines
The Thai submarine does, though, reinforce a different trend: Southeast Asian seas are now arenas of influence as much as force. Every frigate delivery, aircraft sale or missile upgrade carries political weight.
US officials have responded cautiously. The Pentagon publicly stresses that Thailand remains a “long-standing strategic partner” and highlights joint exercises, humanitarian operations and shared objectives for regional stability. In private, American planners will be recalculating how much access, interoperability and trust they can assume in future crises.
How the S26T compares with other export submarines
| Model | Builder country | Displacement | Propulsion | Max endurance | Export customers |
|---|---|---|---|---|---|
| S26T (modified Type 039A) | China | 2,550 t | Diesel-electric + Stirling AIP | ≈ 65 days | Thailand |
| Scorpène | France | 1,700–2,000 t | Diesel-electric + optional AIP | ≈ 50 days | India, Brazil, Malaysia, Chile |
| Type 212A | Germany | 1,800 t | Diesel-electric + hydrogen AIP | ≈ 30 days | Germany, Italy, Norway |
| U214 | Germany | 1,860 t | Diesel-electric + AIP | ≈ 50 days | Greece, South Korea, Turkey |
| Taigei | Japan | 3,000 t | Diesel-electric + lithium-ion batteries | High | Domestic only |
Compared with these models, the S26T sits in the mid-range: bigger than many European designs, less advanced in propulsion technology than Japanese boats, but offering long endurance at a competitive price. That combination appeals to mid-sized navies with tight budgets and growing maritime concerns.
What “hedging” really looks like at sea
The term “hedging” is borrowed from finance. In security policy, it means spreading risk between great powers rather than placing all bets on one guarantor. Thailand trains regularly with US forces but buys major platforms from China. It continues to welcome American exercises like Cobra Gold while signing arms contracts with Beijing.
From Washington’s perspective, the danger is not a sudden defection, but a gradual erosion of influence as allies keep more options open.
If a regional crisis erupted in the South China Sea, Thai leaders would face awkward choices. Would they allow US forces to use Thai ports and airfields, knowing that China supplies key equipment and has become a major investor? Would Chinese technicians remain on Thai bases during a confrontation with the US Navy? Those are precisely the scenarios that keep strategists awake.
Risks and benefits for Bangkok
For Thailand, this approach brings mixed consequences:
- Benefits: more bargaining power with both superpowers, access to cheaper hardware, and reduced vulnerability to US political pressure.
- Risks: complex maintenance chains, interoperability issues with US forces, and suspicion in Washington at a time when security cooperation is being re-prioritised.
The submarine deal also ties Thailand to Chinese technical support for decades. If relations sour, spare parts and upgrades could become leverage. At the same time, China gains a partial window into Thai naval practices, which may concern other ASEAN neighbours and US planners.
Why submarines matter so much in Asia
Submarines are valued in the region because they are hard to track and can threaten larger ships with relatively cheap torpedoes or missiles. For smaller states, a few quiet diesel-electric boats complicate an adversary’s planning and raise the potential costs of aggression.
A useful comparison: a surface patrol vessel signals presence, while a submarine signals uncertainty. An unseen boat can be anywhere within its operating range. Commanders must then allocate more assets to anti-submarine warfare, thinning their forces elsewhere.
That psychological effect is one reason why Southeast Asian countries from Vietnam to Indonesia keep investing in undersea capabilities, even when budgets are tight. Thailand’s return to the submarine game sits squarely in that pattern, but with the added twist of Chinese involvement.
For readers watching similar debates in Europe or the Middle East, the Thai case gives a practical example of how defence procurement choices shape alliances, not just arsenals. A single contract can trigger new training programmes, shared technologies and political expectations that last far beyond the lifespan of any government.