Any person subject to this Act who commits any of the following offences, that is to say,--
         (a) uses criminal force to or assaults his superior officer; or
         (b) uses threatening language to such officer; or
         (c) uses insubordinate language to such officer;
shall, on conviction by court-martial,
     if such officer is at the time in the execution of his office or, if the offence is committed on active service, be liable to suffer imprisonment for a term which may extend to fourteen years or such less punishment as is in this Act mentioned; and
     in other cases, be liable to suffer imprisonment for a term which may extend to ten years or such less punishment as is in this Act mentioned:
     Provided that in the case of an offence specified in clause (c), the imprisonment shall not exceed five years.