The Constitution - The commander in chief clause
While the Framers granted Congress the authority to decide for war, they provided in Article 2, Section 2, that: "The President shall be Commander in Chief of the Army and Navy of the United States, and of the Militia of the several states, when called into the actual Service of the United States." The Framers thus vested command of the military forces in the president, which meant that once Congress authorized military hostilities, the president as commander in chief would exercise authority to conduct and prosecute the war effort. As Hamilton explained in Federalist No. 74: "Of all the cares or concerns of government, the direction of war most peculiarly demands those qualities which distinguish the exercise of power by a single hand." But the designation of the president as commander in chief conferred no warmaking power whatever; it vested in the president, as Hamilton proposed to the convention, only the authority to repel sudden attacks on the United States and to direct war, "when authorized or begun." In this capacity, he would direct those forces placed at his command by an act of Congress.
The Framers adopted the title of commander in chief and its historical usage from England, where it was introduced in 1639 by King Charles I. The title was used as a generic term referring to the highest-ranking officer in a particular chain of command or theater of action. But the ranking commander in chief was always sub-ordinate to a political superior, whether a king, Parliament, or, with the development of the cabinet system in England, a secretary of war. The practice of giving the officer at the apex of the military the title of commander in chief and of making him subject to instructions from a political superior was embraced by the Continental Congress and by most of the states in their early constitutions. When, on 15 June 1775, the Continental Congress unanimously decided to appoint George Washington as "General and Commander in Chief, of the Army of the United Colonies," it issued instructions that kept Washington on a short leash. He was ordered "punctually to observe and follow such orders and directions, from time to time, as you shall receive from this, or future Congress of these United Colonies, or Committee of Congress." Congress did not hesitate to instruct the commander in chief on military and policy matters. This usage had been established for a century and a half and was thoroughly familiar to the Framers when they met in Philadelphia. It is probable that this settled understanding and the consequent absence of concerns about the nature of the post accounts for the fact that there was no debate on the commander in chief clause at the convention. It is telling, moreover, that there was no effort at the convention or at any state ratifying convention to redefine the office of commander in chief.
Hamilton's speech on 18 June captured the essence of the president's power as commander in chief when he stated that the executive was "to have the direction of War when authorized or begun." There was no fear of the legal authority granted by the commander in chief clause, and there is no evidence that anyone believed that his office as commander in chief endowed the president with an independent source of warmaking authority. The narrow, military role of the executive was explained by Hamilton in Federalist No. 69, in which he said the president's power as commander in chief "would be nominally the same with that of the King of Great Britain, but in substance much inferior to it. It would amount to nothing more than the supreme command and direction of the military and naval forces … while that of the British king extends to the declaring of war and to the raising and regulating of fleets and armies,—all which, by the Constitution under consideration, would appertain to the legislature." The president as commander in chief was to be "first General and Admiral" in "the direction of war when authorized or begun." But all political authority remained in Congress, as it had under the Articles of Confederation. As Madison explained it in a letter to Thomas Jefferson in 1798: "The Constitution supposes, what the History of all Governments demonstrates, that the Executive is the branch of power most interested in war, and most prone to it. It has accordingly with studied care vested the question of war in the Legislature."