Many predict that the first shots taken in the next war will disable the ability to command and control forces. Almost immediately, a second front will open in the little-known area of navigation warfare. Adversaries understand that the ability to navigate to the right place at the right time while placing weapons precisely on target is critical to victory. The U.S. Navy’s overreliance on the Global Positioning System (GPS) for navigation is an Achilles’ heel.
Preparing for Navigation Warfare
Navigation warfare consists of “deliberate defensive and offensive actions to assure U.S. [forces’] position, navigation, and timing information (PNT) through coordinated employment of space, cyberspace, and electronic warfare operations.”1 Information warfare, especially cyberspace and electronic warfare, is a large part of navigation warfare. Navigation depends on accurate, precise, and timely data that usually comes from external sources, namely, GPS.
GPS’s main limitation is its susceptibility to adversary jamming with high-powered signals on the same frequencies as GPS. Adversaries also could provide false GPS data to spoof a user. Work has already begun to improve GPS with newer satellites and a stronger jamming-resistant navigation signal (M-code). Unfortunately, this work has experienced significant cost increases and delays.
A recent Government Accountability Office (GAO) report on defense navigation capabilities highlighted the Department of Defense’s (DoD’s) alternate PNT options. Two main alternative technological approaches exist: relative PNT and absolute PNT. Relative PNT uses onboard sensors to track movements and calculate the platform’s position as well as keep time without using external signals. Relative PNT is not susceptible to jamming or spoofing. However, the cumulative effect of small errors in measuring movement degrades positional accuracy over time. Absolute PNT uses external information sources to determine a platform’s position with reference to Earth.2
Alternative PNT technologies can complement each other as well as GPS to provide a more resilient PNT system. The GAO report uses modern cell phones as an example of an existing alternative PNT platform. They have a GPS receiver but also use local cell towers and onboard sensors—such as gyroscopes, accelerometers, and a digital compass—to provide more consistent quality position information. According to the report, “this also allows the cell phone to determine position with limited GPS signal or even without GPS entirely.”
Training for a GPS-Denied Environment
Nearly all naval weapons, ships, aircraft, and submarines rely on GPS for absolute PNT. Recognizing this vulnerability, the Air Force has been preparing for a GPS-denied fight since at least the 2018 Red Flag exercise.3 In contrast, apart from a few GPS-denial exercises such as those Carrier Strike Group 4 conducted in 2020, there is no training for ships to navigate in a GPS-denied environment.4 Instead, the surface fleet relies on ships to conduct their own training and drills. From time to time, there are ships that take it on themselves to practice the art of celestial navigation, as the USS Essex (LHD-2) recently did, but this is far from normal practice.5 The Navy should introduce ships to GPS denial during the training cycle.
Currently, the only alternative PNT technologies available to Navy warships are the inertial navigation system (INS) and celestial navigation. Because INS is a relative PNT system, its accuracy degrades over time because of the accumulation of errors from the sensors measuring motion and the environmental conditions affecting the movement of the platform over the surface of the Earth. Celestial navigation is not a much better option since sextants are not precise instruments and are not effective in bad weather. These deficiencies highlight the need for new alternative PNT technologies and methods.
Three Alternative PNT Systems
While not taught to surface warfare officers, bathymetric navigation only requires an echosounder—also referred to as a fathometer—to measure the water depth.6 Because bathymetry relies on the seafloor, it can be used in all weather. This is how submarines routinely navigate. On submarines, INS is the primary navigation system because submarines cannot receive GPS fixes without coming to periscope depth. Therefore, bathymetric fixes augment the accuracy of INS to fill in gaps between GPS fixes.
For surface ships to navigate like submarines, standards need to be developed for using INS and bottom contour charts. In accordance with the Navigation Department Organization and Regulations Manual, INS positions may be used for up to 24 hours or 14 days, depending on the system installed, when GPS is not updating INS.7 However, techniques for using INS positions on surface ships are not taught to navigators, and the bottom-contour charts needed for bathymetric navigation are not authorized for all ships.
While the surface fleet can begin using bathymetric navigation with standard charts, the single-beam echosounders on surface ships limit its effectiveness. To obtain true bathymetric fixes, the Navy must outfit ships with multibeam echosounders that effectively map the ocean floor. When combined with software to recognize depth curves and automatically plot the ship’s position, bathymetric navigation becomes a new real-time absolute PNT system.
Installing multibeam echosounders will also require peripheral equipment such as expendable bathythermographs (XBTs). XBTs have additional benefits, such as enhancing ships’ ability to measure local sound speed profiles, which improve their antisubmarine warfare capabilities. Multibeam echosounders also can be used to detect and classify mines. By adding a forward-looking object avoidance sonar to supplement the multibeam echosounder, ships can more safely maneuver in a minefield. Thus, a simple navigation instrument can be leveraged to increase surface ship warfighting capabilities.
Another alternative PNT technology is an automated celestial navigation system (ACNS). ACNS systems are electronic star finders that automatically calculate a celestial fix with an accuracy rivaling GPS—within about 50 meters. ACNSs are scheduled to come online in the next few years. In the meantime, ships must rely on traditional celestial navigation that requires clear skies.
A final technology proposed for navigation is magnetic anomaly navigation. Unlike the magnetic field caused by the Earth’s core, the crustal magnetic field has enough variation and is stable enough to be used for precision navigation.8 Like celestial navigation, magnetic navigation is completely passive. Unlike celestial navigation, it is resilient in all weather. It is also nearly impossible to jam since the power required to generate a magnetic field strong enough to disrupt a magnetic sensor from a distance would be cost prohibitive.
ACNS and magnetic anomaly navigation can complement bathymetric navigation to form a robust alternative PNT capability immune from adversary interference and with an accuracy that rivals GPS. In this way, the old techniques of navigation are once again made useful with new technology.
Read the Chart
Not only does the Navy need to look at new technology, it also needs to train crews on forgotten skills needed to maintain navigational situational awareness without GPS. The Navy began transitioning from paper charts to the Electronic Charting Display and Information System–Navy (ECDIS-N) starting with the USS Cape St. George (CG-71) in May 2005.As the then-navigator of Cape St. George stated, “The paperless system . . . eliminates the need to make constant pen-and-ink updates on the paper charts; instead, the corrections are downloaded directly into the computer, ensuring that we are always using the most up-to-date chart information.”9 Little did anyone realize at the time that this transition would mark the beginning of the end of the art of chart work.
What is often overlooked is that the ECDIS-N system on warships, known as the Voyage Management System (VMS), can lull watchstanders and navigators into a false sense of security. Rather than being engaged in the navigation picture, watchstanders can neglect the chart because they do not have to worry about manually plotting fixes.
Digital nautical charts (DNCs) issued by the National Geospatial-Intelligence Agency (NGA) require a lot less work to maintain than paper charts, but they are by no means self-sufficient. Only weekly Notice to Mariners corrections can be downloaded to DNCs. U.S. Coast Guard Local Notice to Mariners corrections and NGA real-time navigation warnings still must be plotted manually. Thus, it remains important to teach chart work.
Without paper-chart skills, the ability of Navy crews to read charts also declined. This led to the greatest source of exasperation during my navigator tour. I regularly noticed that operational planners did not appear to look at charts with much attention to detail. In fact, there were instances when planning decisions were made with a system not approved for navigation. This shows that the surface fleet has its shortcomings when it comes to normal navigation.
Victory at sea begins with navigation. In the next war, the Navy will need the surface fleet to show up on target and on time. Accomplishing this without GPS will require much preparation and using new technologies and old techniques to provide alternative PNT. If it fails to prepare, the Navy will not get to the fight, much less win it.
1. U.S. Army Space and Missile Defense Command/Army Forces Strategic Command, “Navigation Warfare,” Army.mil, 7 September 2016.
2. U.S. Government Accountability Office, Defense Navigation Capabilities: DOD Is Developing Positioning, Navigation, and Timing Technologies to Complement GPS, 10 May 2021.
3. Tyler Rogoway, “USAF Is Jamming GPS in the Western U.S. for Largest Ever Red Flag Air War Exercise,” The Drive, 25 January 2018.
4. Dylan Gresik, “FAA: Navy Exercise Near Florida to Cause Widespread GPS Interference,” Military Times, 17 January 2020.
5. Brett McMinoway, “Stars Guide Essex Home,” Defense Visual Information Distribution Service, 2 March 2022.
6. United States Government National Geospatial-Intelligence Agency, American Practical Navigator: An Epitome of Navigation, 2019 Ed. 1, 449–56.
7. Department of the Navy, COMNAVSURFPACINST 3530.4G, Surface Ship Navigation Department Organization and Regulations Manual, 28 October 2021.
8. Aaron Canciani, “Magnetic Navigation,” GPS.gov.
9. Sperry Marine, “Electronic Chart System to First U.S. Navy Ship Certified for ‘Paperless’ Navigation,” Sperrymarine.com, 15 June 2005.