It may be taken offensively by U.S. Marine Corps Drill Instructors to be referred to as 'Drill Sergeants', which is strictly an Army term in the American military, just as Marines may take offense to being called "soldiers". This is considered to be a grievous insult if done intentionally. The only acceptable address of a drill instructor by a recruit is "sir" or "ma'am." At Officer Candidates School (OCS), candidates are instructed by Drill Instructors who have already served a tour at one of the Recruit Depots. Officer candidates address their instructors as "Sergeant Instructor" (and rank and last name), or "Platoon Sergeant" (and rank and last name). The OCS Platoon sergeant is comparable to the Senior Drill Instructor in an enlisted recruit platoon. In the initial phase of training, officer candidates are trained in almost the same manner, and by the same people, as enlisted Marines, with slight differences reflecting the difference between the responsibilities the candidates will have as second lieutenants and those the recruits will have as junior Marines.