I wouldn't call this a "secret base" or that much of a surprise.
China is secretly building a naval facility in Cambodia for the exclusive use of its military, with both countries denying that is the case and taking extraordinary measures to conceal the operation, Western officials said.
The military presence will be on the northern portion of Cambodia’s Ream Naval Base on the Gulf of Thailand, which is slated to be the site of a groundbreaking ceremony this week, according to the officials, who, like others, spoke on the condition of anonymity because of the matter’s sensitivity.
The establishment of a Chinese naval base in Cambodia — only its second such overseas outpost and its first in the strategically significant Indo-Pacific region — is part of Beijing’s strategy to build a network of military facilities around the world in support of its aspirations to become a true global power, the officials said.
Ummm, China is already a true global power. That official needs to read up.
Anyway, dredges have been at work since January. Of course they are going to build a base there. As always, you need to go to the map room, this time WaPo's:
Right in the center right of the Gulf of Thailand. Gives ready access to their sandbar bases in the South China Sea and just 450nm from the southern exit of same athwart shipping routes from and en route to the Singapore Strait. Get a handful of any competent maritime and international relations professionals together and ask them, "Where would you put bases if you were advising the Chinese?" This would be on the short list, especially if you know the long shared interests between China and Cambodia going back to <dusts off a library shelf> when they both decided they didn't like Vietnamese.
Would you do anything different if you were a growing imperial power with eyes on sea control?
The location seems ideal in a few other ways. This gives them a resort location in a relatively unpopulated location. You can see the Cambodian naval base on the right of the below pic - the location of the Chinese naval base under construction is center screen.
It is in a well protected bay itself. Almost a cove with a 2-nm diameter. That will do nicely.
As her global competitors have moved their distraction from neo-imperial policing actions in Central Asia and the Sahel to a retro European steppe meat grinder, the People's Republic of China steadily, calmly, and with shocking regularity ... progresses along one of her lines of operation, clicking off decisive points as she goes.
Only surprise is that anyone is still surprised! Secret...humm the BRI strategy has been formerly and publicly published for nearly a decade. Just ticking off items on their infrastructure and networking “to do” list while the rest of the world is busy with other things....
Looking at the map, I would say while the bad news is that this base is right in the middle of things, that's also the good news: it's ringed by competitor bases, so not a great parking spot in the middle of a hot war.