Ten minutes into arrant mayhem in this town near the Mexican border, and the gunman, a disgruntled Iraq war veteran, has already taken out two people, one slumped in his desk, the other covered in blood on the floor.

The responding officers — eight teenage boys and girls, the youngest 14 — face tripwire, a thin cloud of poisonous gas and loud shots — BAM! BAM! — fired from behind a flimsy wall. They move quickly, pellet guns drawn and masks affixed.

The Explorers program, a coeducational affiliate of the Boy Scouts of America that began 60 years ago, is training thousands of young people in skills used to confront terrorism, illegal immigration and escalating border violence

“This is about being a true-blooded American guy and girl,”