Much of the coverage of the USS Lassen’s maneuver near the Subi reef in the South China Sea presented the operation as a challenge to Chinese maritime claims and island-building operations. But in fact there are two quite distinct legal issues at play. The first is the traditional U.S. interpretation of the right of innocent passage (even by warships) through territorial waters. The UN Convention on the Law of the Sea provides that military vessels can transit territorial waters provided that they do so expeditiously and without engaging in most military actvities, such as firing weapons or engaging in surveillance. China has often contested the U.S. interpretation of innocent passage.