NEW YORK -- Every newly commissioned ship in the U.S. Navy's surface fleet carries a copy of Nathaniel Bowditch's "The American Practical Navigator" (originally published in 1802) on its bridge. This thick encyclopedia on maritime navigation is packed with data on the latitudes and longitudes of various landmarks -- from the Bugio Lighthouse in Lisbon, Portugal, to the Kannonzaki Lighthouse in Yokosuka, Japan.
It also provides detailed instructions on how to use a sextant to measure a ship's current location by observing the sun, moon, stars and horizon. Though the act of carrying the book on every ship is largely ceremonial, the threat of China's electronic warfare has increased the likelihood that the ship's quartermaster will reach for Bowditch.
The USS Patriot, a mine countermeasures ship based in Sasebo, Japan, traveled 1,100 miles down the west coast of the host country last August relying solely on celestial navigation.
At noon, sailors would take a sextant, a centuries-old instrument, to measure the angle of the sun at its highest point of the day. The data would be fed into a computer program called System to Estimate Latitude and Longitude Astronomically, or STELLA.
Sailors also observed the angular distance between the horizon and the moon, planets and stars to calculate latitude and longitude.
On the ship's bridge, a navigation team consisting of quartermasters, junior officers and the navigator used the data to steer the vessel night and day.
Celestial navigation, or astronavigation, had disappeared from the U.S. Naval Academy's curriculum in 2006 as it was deemed outdated. But in 2015, the school brought back the technique, taking students once again to a planetarium to teach them how to measure and apply the math.
The return was prompted by the recognition that as the U.S. armed forces grow increasingly dependent on digital communication, one blow to the Global Positioning System -- on which this communication relies -- could hobble the world's strongest military. That concern has intensified as China enhances its electronic and cyber warfare capabilities.
"The opening battle of the next major war will be silent," said Peter Singer, a strategist at think tank New America and author of "Ghost Fleet: A Novel of the Next World War."
This battle will not be an attack like the one at Pearl Harbor that drew the U.S. into war with Japan in 1941, or likely have any resemblance to the shock-and-awe opening to the Iraq War in 2003.
"It may already have been fought," Singer said.
In cyberspace, the moves that matter take place weeks, months or years before the war. "You penetrate the network. Then you take advantage of it on that opening day," he said.
If digital communication is knocked out, the Navy goes back to a natural world, relying on eyes and ears to survive -- hence the return of the sextants.
But Singer says there may be two other options beyond the last resort of 18th century instruments.
One is to build a more resilient communications network. Improving cybersecurity might let the military fend off any challenge to GPS.
The second is to develop highly intelligent systems that do not need GPS.
"So, for example, there is research on missiles that will be able to fly by navigating off of magnetic fields," Singer said.
He equated this to the ability of birds to migrate long distances each year and reach virtually the same destination.
"It's not because they memorize it," Singer told Nikkei Asia. "It's their way of sensing the Earth's magnetic fields. Insects are another that do that. So there is high-tech research on essentially developing digital versions of the way that birds and insects navigate."
The Pentagon's Defense Advanced Research Projects Agency (DARPA) is pursuing so-called Adaptable Navigation Systems. This envisioned GPS-quality method for positioning, navigation and timing would be operational even in network-unfriendly conditions such as inside buildings, in urban canyons, under dense foliage, underwater and underground.
In February, a group of scientists including professor Richard Holland of Bangor University and Dmitry Kishkinev, a lecturer at Keele University, published a report that said birds could possess a "global GPS system."
"The remarkable navigational precision displayed by these tiny birds -- as they travel alone over stormy seas, across vast deserts, and through extremes in weather and temperature -- has been one of the enduring mysteries of behavioral biology," the U.K. academics wrote to the World Economic Forum.
"A gathering body of evidence has indicated that the Earth's magnetic field is one of the likeliest solutions to this mystery. It has been suggested that different parameters of the Earth's magnetic field could form a grid, which birds follow," they said.
"If birds have learned that magnetic intensity increases as they go north, they should be able to detect their position on the north-south axis wherever they happen to be," the report said.
This would mean that birds essentially navigate using a system similar to Cartesian coordinates, the basis of modern GPS navigation.
Nikkei Asia asked Holland whether any military application of this system is possible. "In theory, the Earth's magnetic field could be used as a location system," he said.
But he added a caveat. "What is unclear is whether this can be used on a global scale the way a GPS can as there are several locations on the Earth with the same magnetic signature."
Still, this could be the answer sought by the U.S. military in its quest to defend against electronic warfare by China or others.
Billy Fabian, a senior analyst at data and analytics firm Govini and adjunct senior fellow at the Center for New American Security, said that preparing for a scenario under which communications are disrupted will be critical considering the nature of a potential war with China.
"A future conflict between the United States and China will be different from past conflicts in two aspects," he said. "One, every domain will be highly contested, and that's different than what we've become used to -- rapidly being able to gain dominance in all domains and then operate in a realm in a permissive information environment, in a permissive air environment and a permissive sea environment."
"The second thing is that we are going to have tremendous time pressure," he said. "Most of the places where you could conceivably see us going to war in the near future are in China's backyard, but an ocean away from the continental United States."
China "could attempt to achieve their aggressive objectives before we can adequately respond, and it would be difficult to reverse those gains. There is a need for us to act quickly to prevent that."
"So when you put those two things together, there comes a need for the United States to fight inside of these highly contested battlefields in these highly contested environments, early in a conflict without gaining dominance in all domains," Fabian said. "We have to expect that given their cyber capabilities, given their electronic warfare capabilities, given their kinetic capabilities and ability to strike critical nodes, that connectivity will at times -- and potentially for long stretches -- be disrupted, degraded or even denied."
The U.S. Army has been practicing a concept called "mission command," under which junior leaders on the front lines are empowered to plan, coordinate and execute decisions without having to seek guidance from their superiors.
In this way, small units can continue to operate even when communication is disrupted.
"Our rivals are rapidly modernizing their militaries and eroding our advantages," Adm. Michael Gilday, chief of naval operations and the Navy's top officer in uniform, told the Senate Armed Services Committee's subcommittee on readiness and management support in December.
"Critical to the resiliency of our networked fleet is the ability to assure our capabilities in positioning, navigation and timing," Gilday said. "We are investing in alternate sources of PNT, like the Automated Celestial Navigation System, to ensure our Navy can fight and win in GPS-denied or -degraded environments."
In its annual China Military Power report to Congress, the Pentagon noted that the People's Liberation Army created a theater command-level organization called the Strategic Support Force in 2016 to centralize space, cyber, electronic and psychological warfare missions and capabilities.
The creation of the force reflects China's apparent concern about the disparity between its cyber capabilities and those of the U.S., the report said. It added that China's leaders believe that "achieving information dominance and denying adversaries the use of the electromagnetic spectrum is necessary to seize and maintain the strategic initiative in a conflict."
The Strategic Support Force's Space Systems Department, responsible for nearly all PLA space operations, has at least eight bases and runs tracking, telemetry and command stations in Namibia, Pakistan and Argentina, the report said.