By Rebecca Kheel - 01/06/16 03:25 PM EST
Defense Secretary Ash Carter is defending the Navy's patrol of the disputed South China Seas following questions from Sen. John McCainJohn McCainGun-control supporters plan next steps versus NRA Report: Prominent neoconservative to fundraise for Clinton McConnell quashes Senate effort on guns MORE (R-Ariz.) about the operation.
Carter said the patrol was "conducted in full accordance with international law," and was a "a normal and routine operation," in a letter to the Senate Armed Services chairman first obtained and published by U.S. Naval Institute News.
In October, the Navy sent the USS Lassen destroyer within 12 nautical miles of artificial islands in the Spratly archipelago built by China.
U.S. officials have said little publically about the operation.
McCain asked Carter to clarify the Navy's intentions after reports surfaced the ship operated under what is known as "innocent passage" — when a ship takes measures to convey it is passing through waters belonging to another nation without any provocation.
Analysts have said innocent passage could tacitly affirm China’s claims to the disputed waters.
In his letter, Carter said the Navy conducted its operations under innocent passage because it is unclear whether any country has a legitimate territorial claim.
The operation “involved a continuous and expeditious transit that is consistent with both the right of innocent passage, which only applies in a territorial sea, and with the high seas freedom of navigation that applies beyond any territorial sea,” he wrote.
Carter said the Lassen sailed past five maritime features claimed by China, Taiwan, Vietnam and the Philippines. None of the countries were notified prior to the operation, he added.
The Pentagon chief also questioned China's claims to one of the built-up islands, Subi Reef. Prior to China's work, he said it was submerged at high tide, meaning China can't legally claim the territorial waters around the reef.
Subi Reef, though, is within 12 nautical miles of another feature, Sandy Cay, which could fall under their territorial claims.
“Given the factual uncertainty, we conducted the [freedom of navigation operation] in a manner that is lawful under all possible scenarios to preserve U.S. options should the factual ambiguities be resolved, disputes settled and clarity on maritime claims reached,” he wrote.
Challenging other countries claims was less important that ensuring the seaway remained open for navigation, Carter added.
“The specific excessive maritime claims challenged in this case are less important than the need to demonstrate that countries cannot restrict navigational rights and freedoms around islands and reclaimed features contrary to international law as reflected in the [Law of the Sea] Convention,” he wrote.
“We will continue to demonstrate as much by exercising the rights, freedoms and lawful uses of the seas all around the world, and the South China Sea will be no exception.”