U.S. sailors have faced few threats from other blue-water navies for decades, but the new chief of naval operations is warning that is no longer the reality.
In his first message to the force, Adm. Michael Gilday cautioned sailors about potential adversaries gaining numbers and strength. The Navy must be trained and equipped themselves to take them on, he said.
"For the first time in a very long time, we face serious challenges at sea around the world," Gilday, who became the new CNO on Thursday, said in a fleet-wide message.
Other countries will use their maritime forces to threaten freedom of the seas, intimidate their neighbors, and violate international law, he wrote.
Gilday's message was followed by one from the Pentagon about China's "coercive interference" in Vietnam's longstanding oil and gas activities in the South China Sea, highlighting one of several recent escalations in international waters or exclusive maritime zones.
China, according to the State Department, recently sent a survey vessel -- along with armed escorts -- close to Vietnam's coast. It was one of several recent efforts to coerce nations in the region to "reject partnerships with foreign oil and gas firms, and to work only with China's state-owned enterprises," Morgan Ortagus, a State Department spokeswoman, said last week.
Now, the Pentagon is warning that China's efforts violate the region's rules-based international order.
"China will not win the trust of its neighbors nor the respect of the international community by maintaining its bullying tactics," the Pentagon statement reads.
U.S. Marines and sailors in the Persian Gulf also recently shot down at least one Iranian drone that got too close to their ship and are taking new steps to defend themselves against fast boats in the Strait of Hormuz. That's the area where a British tanker was recently seized.
Even if other navies can't take physically take on American ships, Gilday said they'll look for other vulnerabilities.
"They will try to attack our Navy in areas like cyber," said Gilday, who previously served as the head of Navy Cyber Command.
To stay ahead, the CNO said the service will rapidly modernize. There will also be an emphasis on training, he said, calling a well-trained force "our competitive advantage." He plans to release a detailed guidance to the force in 45 days, and said he'll work with leaders, international partners and the Marine Corps to "develop our way ahead to meet these challenges."
The Marine Corps' new commandant, Gen. David Berger, recently said he wants greater integration between the Navy and his service as sailors and Marines face new threats ashore and at sea. Some naval experts have called Berger's planning guidance, in which the commandant shared his vision for naval integration, revolutionary and a game-changer.
Gilday told lawmakers during his nomination ceremony that he is committed to working closely with the Marine Corps as CNO.