Gary Bass was 17 when he joined the Marines. “I really wanted to get out of my small town, and make a difference in the world,” he said.

Mr. Bass, who grew up in Central Point, Ore., went on to a 30-year career in the Marines. He became a sergeant major — the highest enlisted rank in the corps — and, among his assignments, served for four years as a recruiter in the Seattle area. There, he saw many other young men and women enlisting for reasons similar to his.

“They joined because they were patriotic, and because they wanted to be part of something larger than themselves,” he said. “They weren’t joining because of the retirement benefits.”

And yet, over the past year, that is exactly what many Marines — as well as members of every other branch of the United States military — have been talking about.