(1) This section has effect for the purposes of a proceeding for an offence against this Act.
(2) Subject to section 16, it is a defence if the doing by the defendant of the act alleged to be the offence:
(a) was permitted by the laws, customs and usages of war; and
(b) was not under international law a crime against humanity.
(3) To avoid doubt, the doing of the act by the defendant was permitted by the laws, customs and usages of war if it was reasonably justified by the exigencies and necessities of the conduct of war.
(4) The defendant is not entitled to rely on a defence under subsection ( 2) unless there is evidence of the existence of the facts constituting the defence.
(5) However, if there is such evidence, the onus of establishing, beyond a reasonable doubt, that those facts either do not exist or do not constitute the defence lies on the prosecution.