143. The officer who confirms the sentence or such other officer as may be prescribed, may direct that the sentence of imprisonment in any particular case shall be carried out by confinement in a civil prison or by confinement in a military, naval or air force prison, and 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 the person is to be confined, and shall forward him to such prison with the warrant: Provided that in the case of a sentence of imprisonment for a period not exceeding three months, the sentence may be directed to be carried out by confinement in naval custody instead of a prison: Provided further that on active service a sentence of imprisonment may be carried out by confinement in such place as the officer commanding the naval forces may from time to time appoint.