Every Marine, regardless of his military occupation, is trained as a Rifleman. This concept has been around since the Marine Corps inception in 1775, when every man who volunteered was required to bring his own musket.
In the early 1900s, as the Marine Corps grew and additional military occupations were created, the Commandant, General John A. Lejeune, ensured that every Marine, regardless of his Military Occupational Specialty (MOS), received marksmanship training.
During the Korean War, the Marine Corps was the only service to create rifle companies entirely from cooks, drivers, and other non-infantry Marines. From this war, the proverbial saying, Every Marine a Rifleman was born.
In the nineteen eighties, the Commandant, General Al Gray, recognized the need to train all Marines in more than just basic marksmanship, but in modern-day combat skills. The School of Infantry was assigned to conduct this training known as Common Skills because it is common to every Marine. These common skills allow every Marine, regardless of MOS, to act as Rifleman when called upon.