Drill instructor
From Halopedia, the Halo wiki
Drill Instructors (or DI's as some military personnel call them) are UNSC personnel specially assigned to train trainees. They have been used in at least two SPARTAN projects (II and III), though it is unlikely they were used in the first, as the candidates were already in the Military and were adults. In the SPARTAN-II project there were drill instructors for each Spartan trainee In SPARTAN-III, however, there were only 72 drill instructors.
