During the period 1901-1945, Australian courts decided a small number of cases that considered the vexed question of the extent to which the Commonwealth could plead that it should be immune from liability in negligence because the proscribed conduct took place as part of the defence of the realm. Drawing on newspaper and archival records, this paper considers in detail both the reasons for the decisions and their wider historical and political context. While Australian courts unsurprisingly adopted the common law framework for negligence actions, the precise questions for decision had no English parallel and in a very real sense these decisions were at the forefront of imperial common law development. Moreover, the decision in the Leviathan 'Shaw Savill & Albion' case also illustrates the interconnectedness of the substantive rules of law with rules of evidence, and the different approach taken by the High Court from that of the House of Lords on this issue demonstrates yet again that Australian judges of this period were much more innovative than has previously been thought.