law: 166. Execution of sentence of imprisonment.-
  (1) Whenever any sentence of imprisonment is passed under this Act or whenever any sentence of death or transportation is commuted to imprisonment, the confirming officer or such other officer as may be prescribed, shall, save as otherwise provided in sub-sections (3) and (4), direct either that the sentence shall be carried out by confinement in a military or air force prison or that it shall be carried out by confinement in a civil prison.
  (2) When a direction has been made under sub-section (1) the commanding officer of the person under sentence or such other officer as may be prescribed shall forward a warrant in the prescribed form to the officer-in-charge of the prison in which such person is to be confined and shall arrange for his dispatch to such prison with the warrant.
  (3) In the case of a sentence of imprisonment for a period not exceeding three months, the officers referred to in sub-section (1) may direct that the sentence shall be carried out by confinement in air force custody instead of in a civil or military or air force prison.
  (4) On active service, a sentence of imprisonment may be carried out by confinement in such place as the officer commanding the forces in the field may from time to time, appoint.