Matthew Partyka was built for the infantry, not sales. The young, blue-eyed Marine sergeant was a quiet introvert, almost sphinx-like, with a soft smile. He thrived in the brotherhood of combat units.

U.S. Marine Corps Sergeant Jeremiah Grigsby, right, promotes Corporal Alex Akers, both riflemen with 12th Littoral Combat Team, 12th Marine Littoral Regiment, 3rd Marine Division, to the rank of ...