171. Execution of sentence of imprisonment in special cases. -Whenever, the opinion of an officer commanding an army, army corps, division or independent brigade, any sentence or portion of a sentence of imprisonment cannot for special reasons, conveniently be carried out in a military prison or in military custody in accordance with the provisions of Sec. 169 such officer may direct that such sentence or portion of sentence shall be carried out by confinement in any civil prison or other fit place. | 