The USS Decatur, a guided-missile destroyer, has sailed around the vicinity of a number of Chinese claimed islands in the Paracel Islands chain in the South China Sea, in a move US officials say was done primarily to prove to China that they could do so over Chinese objections.

This is just the latest in a series of Pentagon “patrols” through the area, which officially are presented as freedom of navigation operations, but which in the past the Pentagon has repeatedly hyped as being overt challenges to Chinese maritime claims.

This one didn’t require the Pentagon hype, as the Decatur spent so much time loitering around the Paracels that China’s Defense Ministry issued their own statement condemning it as an “illegal” and “provocative” act. China said two of its warships had “warned” the Decatur to leave. The ships were the frigate Luoyang and the Guangzhou, a missile destroyer.

The claims of the patrol being “illegal” are disputed. Recent cases in international law have suggested that unoccupied islands like the ones in question don’t extend a nation’s maritime sovereignty, and that subsequently the ship never technically entered Chinese waters. The US is keen to make this claim, though at the same time they went in knowing China’s position, and therefore the claim it was provocative was definitely a fair one.