Laymen whose only sources of information about Marine Corps enlisted training are movies and TV shows tend to envision a single Drill Instructor (DI) handling all the training of a platoon. In reality, the training is the responsibility of a team of three or four Drill Instructors organized into a hierarchy based both on experience and duties.
The least experienced member of a team is referred to as an Assistant or Junior Drill Instructor (but not by recruits, who call them Drill Instructor or DI), who is in charge of overseeing constant practice of closer-order drills. More experienced DIs are tasked with training and overseeing platoon discipline. At the top is the Senior Drill Instructor, the Noncommissioned Officer in Charge (NCOIC) of both the platoon and the subordinate DIs.
Senior Drill Instructors are visually set apart from lower-level DIs by the black leather belt they wear with a brass buckle. All other DIs on the team wear green web pistol belts with a quick release buckle.