For centuries, if you wanted to navigate a ship any distance you used charts and a sextant, or one of its predecessors. The sextant was instrumental in helping sailors, and early pilots, figure out longitude and latitude by taking sightings of the sun, stars and moon at specific times.
Then along came more advanced means of navigation, leading to our current network of GPS satellites that can position a ship on a digital map with pinpoint accuracy in just seconds. With that kind of speed and precision, it's no surprise that the Navy stopped teaching traditional celestial navigation 20 years ago. Now, however, it's coming back.
Midshipmen at the Naval Academy are getting a three-hour course in the basics of celestial navigation. Naval ROTC is also going to start programs around the country to bring the skill back. They're both getting help from the Merchant Marine Academy, which never stopped its celestial navigation courses.
The reasoning for bringing back this "low-tech" approach is that in a major 21st century war, a quick way to disable your opponent is to knock out their technology. If a foreign power managed to take down the GPS network or disrupt shipboard electronics, it would leave our ships literally lost at sea. In that case, a sextant and charts could save the day.
Other branches of the military have done similar things in the past. For example, Air Force radar operators during the Cold War had to be able to calculate incoming missile trajectories using a slide rule if the computers failed.
Want to know more about what a major 21st century war could look like? Listen to Kim's insightful podcast interview with P.W. Singer, author of "Ghost Fleet," which goes in-depth on the challenges and dangers of warfare in the digital age.