Hong Kong(CNN) Two US Navy admirals in charge of a rare South China Sea exercise say "extraordinary" coronavirus measures taken by the service, including requiring all sailors to wear face masks, have left their aircraft carrier strike groups in a high state of readiness in one of the most tense maritime environments in the world.
The Navy's response to the pandemic comes after one of its Pacific-based carriers, the USS Theodore Roosevelt, was crippled for weeks earlier this year by an outbreak that infected hundreds of its crew.
"We've taken extraordinary measures to protect our sailors from Covid, but that said it remains a real threat and requires constant vigilance," Rear Adm. George Wikoff, commander of Carrier Strike Group 5, led by the USS Ronald Reagan, said Wednesday in a phone call about the South China Sea deployment.
"The entire team underway, everyone on board, is required to wear a mask," Wikoff said.
The Navy has also spaced out mealtimes, instituted social distancing and brought aboard specialists including microbiologists and extra health personnel, said Wikoff and Adm. James Kirk, commander of Carrier Strike Group 11, led by the USS Nimitz.
"Those measures have all been effective, and we are sailing Covid-free right now," Wikoff said.
Wikoff and Kirk spoke to CNN after leading their groups, totaling more than 12,000 sailors and aviators, in a dual-carrier deployment to South China Sea, the first time two of the US Navy's massive warships have exercised in the region in six years.
The deployment, which saw the two carriers and their escorts operate 24 hours a day while launching hundreds of aircraft sorties daily, comes as the US itself is struggling with a surge in Covid-19 cases and how to stem infection rates.
There is division in the country on wearing masks, enacting social distancing measures and when and to what degree to open everything from stores to schools to sports stadiums.
With tens of thousands of new infections being reported in the US daily, the country is nearing 3 million infections in total since the coronavirus outbreak began earlier this year.
More than 1,000 of those Covid-19 cases were among the crew of the Theodore Roosevelt, which was left tied up in Guam for weeks in the spring.
Smaller outbreaks were reported among crews of both the Reagan and Nimitz, but Kirk said the Navy turned that situation around.
"The strike group has remained Covid-free since early April," Kirk said Wednesday.
"We've been very effective in applying the mitigation measures that have been put in place to protect the health and readiness of the crew and the strike group," he said.
The earlier outbreaks left the US Navy open to criticism by rival China, which touted its readiness while the Pentagon fought the virus on US ships.
Analyst Carl Schuster, a former director of operations at the US Pacific Command's Joint Intelligence Center, said the dual-carrier exercise in the South China Sea was designed to send a message to Beijing. "The US Navy is back following the Covid-19-driven reduced activity," Schuster said.
The admirals said Wednesday their deployment to the South China Sea, almost all of which China claims as its territory, was intended to underscore the US Navy's commitment to a free and open Indo-Pacific. "If there are nations that have excessive claims, we will challenge those," Kirk said.
Beijing on Monday labeled the US' presence in the region as destabilizing.
"The US action is intended to drive a wedge between countries, promote the militarization of the South China Sea, and undermine peace and stability in the South China Sea," Chinese Foreign Ministry spokesperson Zhao Lijian said at a briefing.
In a report in China's state-sponsored Global Times, Beijing called the US carriers "nothing more than paper tigers on China's doorsteps" and said Beijing has more than enough firepower to defend its positions in the South China Sea.
"The South China Sea is fully within the grasp of the People's Liberation Army (PLA), and any US aircraft carrier movement in the region is closely watched and taken aim at by the PLA, which has a wide range of anti-aircraft carrier weapons like the DF-21D and DF-26, which are both regarded as 'aircraft carrier killer' missiles," the Global Times report said.
"Any US #aircraftcarrier movement in the region is at the pleasure of PLA," Global Times tweeted, along with pictures of the Chinese missile.
The US Navy quickly responded:
"And yet, there they are. Two @USNavy aircraft carriers operating in the international waters of the South China Sea. #USSNimitz & #USSRonaldReagan are not intimidated #AtOurDiscretion," the US Navy's chief of information tweeted.
For all the web-based rhetoric, the two admirals said their operations in the South China Sea were routine.
They said that Chinese warships monitored the US exercises, but the operations were professional and safe.
"We certainly saw the PLA Navy and they saw us," said Kirk.