Port call by Japanese vessels at Ream Naval Base highlights tensions over China’s growing influence in Southeast Asia.

Ream naval base on Cambodia’s southern coast has raised concerns in the United States. (c) Planet Labs PBC/AFP

By Anna Fadiah and Hayu Andini

Two Japanese warships made a historic port call at Cambodia's Ream Naval Base on Saturday, becoming the first foreign vessels to dock at the recently renovated facility, according to a statement from the Japanese embassy in Phnom Penh. This visit is significant as the base has drawn international attention—particularly from the United States—due to concerns over its reconstruction with Chinese assistance. The presence of Japanese warships at the site signals not only a maritime development but a geopolitical one, placing Japan in a delicate diplomatic position amid growing U.S.-China rivalry in Southeast Asia.

The Japanese warships—JS Bungo and JS Etajima, both part of the Japanese Maritime Self-Defense Force (JMSDF)—docked quietly at Ream, where media access was restricted. The Japanese embassy called the visit “historically significant,” underscoring Tokyo’s support for an open and multilateral approach to regional military facilities. “We are aware that the Royal Government of Cambodia has been willing to make the base open to all the countries,” the embassy stated, reinforcing the idea that Ream is not a closed, Chinese-exclusive operation.

This visit comes at a time of heightened scrutiny over Cambodia’s naval operations, as Japanese warships dock at Cambodia naval base facilities that were originally developed with partial U.S. funding but are now being significantly upgraded with help from China.

A naval base at the center of strategic tensions

Ream Naval Base, situated along Cambodia’s southern coastline on the Gulf of Thailand, has been at the heart of strategic debates for several years. The United States has raised concerns that the facility, once jointly supported by Washington and Phnom Penh, is being transformed into a hub for the Chinese military. The strategic location near the disputed South China Sea—a region Beijing claims almost entirely—only adds to those concerns.

These fears were amplified by reports in 2022 suggesting that parts of the base would be reserved for exclusive use by the Chinese navy. Such an arrangement would give China a critical foothold in Southeast Asia, one that could potentially threaten regional stability and challenge the freedom of navigation operations regularly conducted by U.S. and allied naval forces.

Despite repeated denials from Cambodian officials, skepticism remains. Cambodia’s Prime Minister Hun Manet, who took office in 2023, has stated that the base has “nothing to hide” and is open to vessels from all friendly countries. His remarks came during a ceremony earlier this month, where he was joined by a delegation from China’s People’s Liberation Army to inaugurate the newly upgraded base.

Still, the optics of a China-funded military facility in one of Beijing’s closest allies in Southeast Asia raise valid geopolitical questions.

Japan’s balancing act in Southeast Asia

The decision by Japan to send warships to Ream is a carefully calibrated move. As a close ally of the United States, Japan shares many of Washington’s concerns about China’s rising influence and assertiveness in the Indo-Pacific. However, Tokyo also has a longstanding commitment to regional engagement and maintaining open lines of communication with Southeast Asian countries, including Cambodia.

By sending JMSDF ships to Cambodia, Japan demonstrates a form of diplomatic engagement that contrasts with direct confrontation. The message appears to be one of openness: if Cambodia claims Ream is available to all, Japan is testing that claim and encouraging transparency.

The Japanese government, through its embassy, acknowledged the diplomatic significance of the port call. “This visit will enhance trust and confidence,” the embassy noted, suggesting that Tokyo views its presence at Ream as not only a military engagement but also a form of soft power diplomacy.

China’s expanding influence in Cambodia

The Japanese warships’ visit occurs just days after Chinese President Xi Jinping concluded a tour of Southeast Asia, where he stopped in Cambodia to bolster regional trade ties. Xi’s visit reaffirmed the growing bond between Beijing and Phnom Penh—a relationship that has deepened over the past decade through billions of dollars in Chinese infrastructure investment.

Under former Cambodian Prime Minister Hun Sen—Hun Manet’s father—China emerged as Cambodia’s largest foreign investor and donor. While these investments have spurred development, they have also given Beijing considerable sway over Cambodian politics and military infrastructure.

Japan’s port call, then, could be interpreted as a subtle counterbalance to China’s influence. It also aligns with Tokyo’s broader Indo-Pacific strategy, which seeks to promote peace, security, and cooperation in a region where power dynamics are increasingly fluid.

The Japanese warships docking at Cambodia naval base sends a clear message—not only to Cambodia but to the broader region. The port call underscores Japan’s continued maritime presence and willingness to engage even in areas where China’s influence is strongest.

It also comes amid broader tensions over military access and basing rights in Southeast Asia. The United States, while publicly affirming respect for Cambodia’s sovereignty, has expressed deep unease over the lack of transparency surrounding the Ream renovation. U.S. officials fear that Chinese military access to Ream could alter the strategic balance in the Gulf of Thailand, potentially limiting American maneuverability in the region.

Japan’s visit to the base may help alleviate some of those concerns by showing that Cambodia is willing to host multiple foreign navies. Yet it also raises the stakes: if the base is truly open, as Hun Manet claims, future port calls by regional and Western powers could become a new front in the contest for influence.

Cambodia’s careful messaging

For Phnom Penh, allowing Japanese ships to dock at Ream serves multiple purposes. It helps defuse criticism that the base is exclusively for Chinese use and affirms Cambodia’s official position of neutrality. It also signals to other regional partners—especially ASEAN members—that Cambodia remains open to engagement, even if its relationship with China is especially close.

Still, the Cambodian government has been cautious. Media were not allowed access to the base during the Japanese visit, and official commentary from Phnom Penh has been minimal. This lack of transparency continues to fuel speculation about the base’s true purpose.

Hun Manet’s administration must now navigate a complex web of interests: reassuring China of its strategic alliance, maintaining diplomatic relations with the U.S. and Japan, and preserving Cambodia’s regional credibility.

As Japanese warships dock at Cambodia naval base facilities upgraded with Chinese help, a new chapter in Southeast Asian maritime diplomacy is unfolding. This event may seem minor in isolation, but it reflects larger geopolitical shifts playing out across the region. The next steps—whether more countries send ships to Ream, whether Cambodia increases transparency, and how China responds—will shape the narrative.

For Japan, the port call demonstrates commitment to peace and regional cooperation. For Cambodia, it’s an opportunity to show it can play host to all powers, not just one. And for China and the United States, it’s a reminder that the contest for influence in Southeast Asia is far from over.

As the waters of the Gulf of Thailand become more crowded with naval power, the real test for Cambodia will be whether it can maintain its promise of openness—or whether the shadow of exclusivity will return.