Over the last three years, the U.S. military has shelled out a staggering $6 billion just to bring in new recruits and keep current service members from leaving. It’s part of a bigger push to tackle a persistent problem: not enough people signing up.

Editor’s Note: The military’s spending spree highlights how tough it’s gotten to attract and hold onto troops—a sign of shifting attitudes toward service, a tight job market, or maybe both. If enlistment keeps dropping, it could force even bigger changes in how the Pentagon fills its ranks.