The Marine Corps formed a task force this fall in response to the battalion’s plight, but it has largely focused on how to prevent suicides in future veterans. The V.A. said in a statement that it could not contact members of the battalion and other war-scarred units because some members may still be in the military and therefore outside the V.A.’s authority.

“I don’t understand — they should at least do something,” Madelyn Gould, an epidemiologist at Columbia University who helped create national guidelines on responding to suicide clusters, said in an interview.

Clusters can form in tightknit groups, such as schools or military units, she said, where one death can spur others until suicide becomes what she called “a cultural norm.” She said care providers could intervene to discuss the problem and teach effective ways to respond and cope. But that requires identifying those groups and reaching out to them.

Friends said Mr. Schlagel often dismissed suicides in the battalion — including the deaths of two friends — as cowardly acts. His stance made his death that much more perplexing to the others.

“I didn’t see it coming, not from him,” a battalion member, James McKendree, posted to other members’ Facebook pages the day after his death. “Why our battalion? I’m at a damn loss. The VA can’t fix it. WE have to fix it. YOU have to fix it, and I’m talking to every 2/7 vet out there. You’re not a VICTIM. Quit drinking / pill-popping yourself into oblivion. Pull yourself up by your damn bootstraps.”

A few days later, the song of a solitary bugle playing taps floated through frigid morning air at a cemetery near the farm where Mr. Schlagel grew up.