Armed guards stand at the gates. IDs are needed to pass through electronic barriers. And uniformed members of the American military — well-trained and battle-tested — are everywhere, smartly saluting as they come and go.
And yet, twice in less than four years, a person with permission to be there passed through the layers of protection at a U.S. base and opened fire, destroying the sense of security at the installations that embody the most powerful military in the world.
‘‘It is earth-shattering. When military bases are no longer safe, where is safe, if that even doesn’t exist anymore?’’ said Col. Kathy Platoni, a reservist who keeps a gun under her desk after witnessing the shooting at Fort Hood in Texas in 2009, when Army psychiatrist Maj. Nidal Hasan killed 13 people. Full story for BostonGlobe.com subscribers.