WASHINGTON • As unmanned aerial drones have become a critical part of modern warfare, attention has turned to the depths of the oceans, with the US Navy ahead in the race to deploy autonomous robots underwater.
While Russia and China are investing in their submarine fleets, the Pentagon has sought to seize an advantage by introducing new technologies for its undersea systems.
The Pentagon said the underwater drone seized by the Chinese last Thursday was part of an unclassified "ocean glider" system used around the world to gather data on salinity, water temperature, sound speed and other factors that may affect US naval operations.
Though the Pentagon described it as an unclassified operation, defence experts told The Wall Street Journal the US often uses data from such drones to track foreign submarines and navigate US submarines.
China's move to seize the drone marks an escalation of Beijing's efforts to block US naval surveillance and likely reflects rising concern about the United States tracking Chinese submarines, according to The Wall Street Journal.
The Pentagon plans to invest as much as US$3 billion (S$4.3 billion) in undersea systems in the coming years, according to the Washington Post in a report last month.
The US Navy has been testing and fielding several new systems designed to map the ocean floor, seek out mines and submarines, and even launch attacks, reported the Post.
US military officials say there is a sense of urgency because the undersea domain could one day be as contested as the surface of the sea, the skies - and even space, according to the Post.
"The Pentagon feels like the US is well-positioned to do undersea warfare and anti-submarine warfare better than any other country," said Mr Bryan Clark, a senior fellow at the Centre for Strategic and Budgetary Assessments. He is the author of a report titled "The emerging era in undersea warfare".
In April, US Defence Secretary Ashton Carter spoke about the deployment of new undersea drones in the disputed waters of the South China Sea. The Pentagon's investment in subs "includes new undersea drones in multiple sizes and diverse payloads that can, importantly, operate in shallow water, where manned submarines cannot", he said.
That he chose his visit to the US aircraft carrier Stennis, sailing in the South China Sea, to make the announcement sent a clear message to China, analyst Mark Valencia said in a commentary published in the South China Morning Post.
The unmanned undersea vehicles, or UUVs, are becoming part of the US' plan to deter China from trying to dominate the region, reported the Financial Times.
The initial role of the UUVs is likely to be surveillance, but they could also be used to track enemy submarines, release a series of much smaller drones that could be mines or even launch their own missiles.
Compared with what aerial drones face in the sky, UUVs operate in a far harsher environment.
"Saltwater corrodes metal. Water pressure can be crushing at great depths. And communication is severely limited, so the vehicles must be able to navigate on their own without being remotely piloted," said the Post article published late last month.
While that may be a long way off, the Pentagon is testing vehicles that are capable of going out for weeks or even months at a time, reported the Washington Post.
This year, Boeing debuted the Echo Voyager, an autonomous submarine with the ability to stay out for months; it is not dependent on a support ship the way others are.
This year, General Dynamics boosted its underwater offerings when it acquired Bluefin Robotics, which makes underwater robots.