Hugo Grotius, in his work Mare Liberum, asserted that the world's oceans were free and incapable of acquisition by states. His work sparked a debate in the seventeenth century as to the freedom of the seas, and whether states could exclude the vessels of other states from certain waters. Grotius' viewpoint ultimately prevailed, and is still prevalent within the law of the sea. Greater security concerns of states since 11 September 2001, have raised questions as to the current extent of the doctrine of freedom of navigation, and whether the old norm remains intact. This article will consider this issue, and determine if the right to navigate freely across the world's oceans has been circumscribed. It will also attempt to apply the law to the collision of United States of America and Chinese military aircraft over the South China Sea.