Although, broadly speaking, the constitutional provisions designed for the protection of individual rights are operative in war as well as in peace, the incidents of war repeatedly give rise to situations in which judicially enforceable constitutional restraints are inapplicable. In the first place persons in enemy territory are entirely beyond the reach of constitutional limitations. They are subject, in relation to the war powers of the National Government, to the laws of war as interpreted and applied by Congress and by the President as Commander in Chief. To the question: "What is the law which governs an army invading an enemy's country?" the Court gave the following answer in Dow _v._ Johnson:[1292] "It is not the civil law of the invaded country; it is not the civil law of the conquering country: it is military law,--the law of war,--and its supremacy for the protection of the officers and soldiers of the army, when in service in the field in the enemy's country, is as essential to the efficiency of the army as the supremacy of the civil law at home, and, in time of peace, is essential to the preservation of liberty."[1293]
That substantially the same rule, resting on the same considerations, applies in the field of active military operations, was assumed by all members of the Court in Ex parte Milligan.[1294] There the Court held that the trial by a military commission of a civilian charged with acts of disloyalty committed in a part of the country which was remote from the theatre of military operations, and in which the civil courts were open and functioning, was invalid under the Fifth and Sixth Amendments. Although unanimous in holding that the military tribunal lacked jurisdiction to try the case, the Court divided, five-to-four, as to the grounds of the decision. The point on which the Justices differed was which department of the Government had authority to say with finality what regions lie within the theatre of military operation. Claiming this as a function of the courts, the majority held that the theatre of war did not embrace an area in which the civil courts were open and functioning.[1295] The minority argued that this was a question to be determined by Congress.[1296] All rejected the argument of the government that the President's determination was conclusive in the absence of restraining legislation. A similar result was reached in Duncan _v._ Kahanamoku[1297] where, upon an examination of the circumstances existing in Hawaii after Pearl Harbor, a divided Court found that the authority which Congress had granted to the Territorial Governor to declare martial law "in case of rebellion or invasion, or imminent danger thereof," did not warrant the trial of civilians by military tribunals.