For the first time in 40 years, Taiwan has confirmed a contingent of US special forces is on the island to train its troops.
It's a move that could escalate tensions with Beijing.
A statement from Taiwan's Naval Command is the first time such high-level military co-operation has been admitted in decades, reports Taiwan News.
"In order to maintain regional peace and stability, the military and security co-operation and exchanges between Taiwan and the US are proceeding normally," Naval Command said in a statement.
Groups of US special forces attending annual joint training operations in the small democracy is nothing new. What is new is the acknowledgment of the arrangement.
"This marks the first public confirmation of US military exchanges involving US Marines in Taiwan since the cessation of diplomatic relations between Taiwan and the United States in 1979," the national news service reports.
Beijing has so far refrained from commenting on what is a direct slap in the face for the aggressive Taiwan assimilation message being broadcast by its "wolf warrior" diplomats.
But the move comes as the 20 million-strong island nation reacts with increasing alarm to Beijing's brutal suppression of Hong Kong and a dramatic step-up in Chinese military activity around its borders.
The Communist Party-controlled Global Times news service quoted a defence analyst as stating: "The US military's presence in Taiwan used to be an open secret, and neither side actively gave publicity to related developments.
"But this time, Taiwan announced it in a high-profile way because the DPP wanted to give the impression that it has the US support, no matter who wins the US election."
The response is tame in comparison to Communist Party messaging in September.
"Returning US forces to Taiwan will trigger reunification by force," the Global Times declared.
The US military presence, however, is only temporary.
Taiwanese Marines will reportedly work with the US Marine Raider special operations unit for the next four weeks at the Tsoying Naval Base in the Kaohsiung district. The US Marines undertook a two-week Covid-19 hotel quarantine before being released for the exercise.
Much of the operation will take place at sea and along the coast. Troops will use new assault boats and personal equipment. Taiwan's military has stepped up its preparations to resist an invasion, with exercises including urban warfare and dispersion tactics.
The presence of the US Marines isn't the only joint exercise with Taiwan this year. US Navy Seal frogmen train their counterparts annually in Operation Flash Tamper.
The annual Balance Tamper exercise places US Army Green Berets special forces among elements of the ROC Army Aviation and Special Forces Command.
While these are also never publicly acknowledged, the US Army released a video earlier this year showing a specialist reconnaissance unit working with Taiwanese troops.
But analysts have pointed to the timing of the US Marine visit.
Taipei has invested an extra $US29 million (NZ$42m) in modernising and strengthening its small naval marine force. The unit is expected to defend Taiwan's South and East China Sea island assets, as well as to conduct counter-terrorism and counter-incursion operations.
Washington formally recognised Chinese Communist Party control of Beijing in 1979. Since that time, it has adopted a policy of diplomatic ambiguity over the sovereignty of Taiwan.
The "One Nation, Two Systems" argument was accepted in the hope of further encouraging Beijing to open up and engage with the world economy.
With the rise of Chinese Chairman-for-life Xi Jinping, those hopes have turned sour.
In late October, US and Chinese military commanders held talks to establish channels for "crisis communications" in the case of an "event" in the disputed South and East China Seas.
The two-day video conference also addressed Beijing's fears that Washington was about to launch a sudden drone attack on its illegal South China Sea artificial island fortresses.
"The two sides agreed on the importance of establishing mechanisms for timely communication during a crisis, as well as the need to maintain regular communication channels to prevent crisis and conduct a post-crisis assessment," a Pentagon statement said.
Meanwhile, Beijing has been hardening the language used to communicate its demand that democratic Taiwan is isolated from international trade, diplomacy and defence networks.
"If the US does deploy troops to Taiwan, it not only breaks the Three Joint communiques fundamental to China-US diplomatic relations but also triggers articles in China's Anti-Secession Law and enables the state to employ non-peaceful means and other necessary measures to protect China's sovereignty and territorial integrity," Communist Party military television commentator Song Zhongping said in September.
"Despite that, the US has been enhancing military co-operation with Taiwan island, including sending military consultants, the US military has remained cautious in stationing troops in the island because it knows this kind of action will send China-US relations back to pre-1979 level, a status of confrontation."