Even as a non-party to UNCLOS, US navigational rights have been protected for decades through customary international law

In 1993, the Department of Defense issued an Ocean Policy Review Paper on “the currency and adequacy of U.S. oceans policy, from the strategic standpoint, to support the national defense strategy.” The paper concluded that U.S. national security interests in the oceans have been protected even though the U.S. is not party to UNCLOS:

U.S. security interests in the oceans have been adequately protected to date by current U.S. ocean policy and implementing strategy. U.S. reliance on arguments that customary international law, as articulated in the non-deep seabed mining provisions of the 1982 Law of the Sea Convention, and as supplemented by diplomatic protests and assertion of rights under the Freedom of Navigation Program, have served so far to preserve fundamental freedoms of navigation and overflight with acceptable risk, cost and effort.

Almost 20 years later, there is no evidence that suggests a change in circumstances such that U.S. accession to UNCLOS has become essential to the successful execution of the U.S. Navy’s global mission.