That’s the problem facing military planners as they try to sort through the increasing reliance of equipment and troops on positioning data from satellite networks at a time when the vulnerabilities of GPS are becoming more apparent.

This month, a group of hackers managed to break into ship-tracking software to spell out the word “pwned,” hacker speak for a successful conquest. And over the summer, a group of students at the University of Texas figured out how to send ships off course using fake GPS signals.