The use of lethal force to prevent terrorist attacks raises a range of legal, moral and policy challenges. This note examines recent legislative changes in Australia which empower the military to use lethal force against hijacked aircraft. These special powers are contained in Part IIIAAA of the Defence Act 1903/em> (Cth), which deals with the `call out' of the military in aid of civil power. These powers to use reasonable and necessary force depart from the conventional criminal law doctrines of necessity and self defence, embracing a broader national security paradigm. This paradigm shift is reflected in the inclusion of powers to use lethal force to protect designated critical infrastructure and a special defence of superior orders. As the note concludes, these reforms reveal the growing influence of international law, particularly the law of armed conflict, on the development of domestic criminal law in Australia