US naval operations in the South China Sea are built primarily around needling China. China has built up a number of islands and claims ownership of them. The US insists China doesn’t own them, and also that they’re not really islands, so the USS Decatur, a guided-missile destroyer, was sent to sail past one of the islands, as a way to thumbing their nose at Chinese claims.
That doesn’t work for China, who sent one of their own destroyers to intercept the American ship, which was just 12 nautical miles off the Spratly Islands. China called the US ship’s presence a “threat” and said the Chinese ship was sent there to tell them to leave.
US officials are now furious as well, both because they intend to keep sailing past those islands to spite China, and because they say China’s ship was “unsafe” in getting so close to them, forcing the USS Decatur to move to prevent a collision.
US officials tend to over-emphasize the “unsafe” operations of anyone confronting US warships, especially pushed when tensions are mounting, as the US-China tensions have been in recent weeks.
Two destroyers 45 yards from one another is close, but not unnavigable. China’s ship forced the US ship to turn, which was the whole point of the interception, to chase the USS Decatur out of what China considers their territorial waters.
Generally, a ship passing 12 miles from a small island would barely be noticed, and China has previously ignored such operations. The Pentagon, however, have emphasized that they are explicitly flouting Chinese territorial claims with such sail-bys, and China apparently felt obliged to respond.