Henry Knox, a Founding Father of the United States, was a Boston bookseller who became a senior general of the Continental Army during the Revolutionary War, serving as chief of artillery in most of Washington's campaigns. Following the American Revolution, he oversaw the War Department under the Articles of Confederation from 1785 to 1789. Washington, at the start of his first administration, appointed Knox the nation's first Secretary of War, a position he held from 1789 to 1794. He is well known today as the namesake of Fort Knox in Kentucky, the repository of a large portion of the nation's gold reserves.

The United States Department of War, also called the War Department, was the United States Cabinet department originally responsible for the operation and maintenance of the United States Army, also bearing responsibility for naval affairs until the establishment of the Navy Department in 1798, and for most land-based air forces until the creation of the Department of the Air Force on September 18, 1947.