Military pilots who only flew centerline thrust multiengine aircraft (most USAF/USN fighters, T-38, and maybe one or two other types) can take the Mil Comp-Instructor written test and be given a CFI-I certificate. However, it will NOT have an airplane rating on it. So, while essentially useless in practice it does allow one to skip the initial instructor practical with an FAA examiner and skip to a practical with a DPE for their CFI or MEI once they've practiced the required maneuvers in the PTS.