Possible Clues:

• Ones getting base pay?: Abbr.
• Sgt. and sgt. maj.
• Cpls. et al.
• No C's, and no commissions, either
• E-4's, E-5's et al.
• Base runners?: Abbr.
• Rank leaders?: Abbr.
• Sergeants and corporals
• Sgts., cpls. and such
• They're not in private practice