Tension grows between the US and China in the South China Sea 2:52
Hong Kong (CNN) - Military watchers online saw something unusual when photos circulated this week that appear to show a Chinese submarine using an underground base on Hainan Island in the South China Sea.
The satellite image of the US company Planet Labs, first published on Radio Free Asia's social media accounts, shows what appears to be a Type 093 nuclear-powered attack submarine entering a tunnel to an underground pier in the Yulin Naval Base.
It immediately sparked comparisons to a spy movie and a Twitter user simply typed the words "Bond, James Bond" in reaction to the photo. Others made reference to the fictional Nautilus, from Jules Verne's novel " 20,000 Leagues Under the Sea."
This August 18, 2020 satellite image appears to show a Chinese submarine using an underground base on Hainan Island in the South China Sea.
Drew Thompson, a former US Defense Department official who now works at the Lee Kuan Yew School of Public Policy at the National University of Singapore, said the image of the submarine is unusual.
"It's unusual for a commercial satellite to be flying overhead at the right time" on a cloudless day, he said.
What is not unusual is the Chinese underground base. This is how Beijing hides much of its military equipment, from submarines to inland-based missile systems, Thompson said.
"The Chinese have a lot of experience in building underground facilities," Thompson said. "It is in accordance with their strategic culture."
But the Chinese coasts receive special attention. "They have an ingrained sense of the acute vulnerability of their shoreline to attack," Thompson said.
CNN has reached out to Chinese authorities for comment on the images.
The Yulin base, at the southern tip of Hainan Island, nearly 470 kilometers southwest of Hong Kong, is one of China's key facilities to protect its naval assets.
As for the submarine, Thompson said its presence at the base does not send any particular signal about the People's Liberation Army Navy.
"The bottom line is that they have a large and growing submarine fleet that is improving in quality," he said.
"They can protect it with underground facilities."
And it keeps submarines out of prying eyes.
At least once this year, on May 15, the U.S. Navy sent one of its P-8A Poseidon reconnaissance and intelligence aircraft on a flight near the Yulin base, naval spokesman Reann confirmed to CNN. Mommsen.
"That's the job of naval intelligence," Thompson said. "Watching an opponent is a daily effort."
And the tunnels can make it frustrating for US military planners, said Carl Schuster, former director of operations for the US Pacific Command's Joint Intelligence Center.
"There is no evidence of combat readiness, operational response times and availability (of the submarine)," he said. "The tunnels blind potential opponents to the status and operational patterns of the submarines, denying them the ability to determine the status of China's military preparations, critical knowledge for assessing China's intentions and plans."
As for the submarine itself, if it is a Type 093, it would be one of six in the Chinese fleet, according to the nonprofit Nuclear Threat Initiative.
The Type 093 comes in three versions and can be armed with torpedoes and cruise missiles, he said.