57. Any person subject to this Act who attempts to commit any offence ¹[specified in this Act] and in such attempt does any act towards the commission of the offence shall, on conviction by court martial, where no express provision is made by this Act for the punishment of such attempt, be punished, if the offence attempted to be committed is punishable with death, with rigorous imprisonment for a term which may extend to fourteen years or with such less punishment as is in this Act mentioned; and if the offence attempted to be committed is punishable with rigorous imprisonment, with rigorous imprisonment for a term which may extend to one-half of the longest term provided for that offence, or with such less punishment as is in this Act mentioned.