In order to ensure the freedom of using world's oceans, since 1979 the United States has been challenged the coastal states' claim of maritime rights with the name of "Freedom of Navigation". The main challenge were those countries that excessive maritime claims. United States not only declares to ensure the right to freedom of navigation on the high seas, but to carry out "freedom of navigation operations" (FONOPs) to challenge those countries claim the waters not in compliance with the international law of the sea. Recently, US executes the FONOPs in South China Sea Waters many times. In terms of international law, some of the US's freedom of navigation operations were indeed in compliance with the UNCLOS, but others were indeed many ambiguities that can be explained by the law, such as warships performing the right of innocuous pass.