Also known as: DoW · DOW · War Department · Secretary of War
The historical U.S. department that ran the Army from 1789 to 1947, and, since a 2025 executive order, a secondary name for the Department of Defense.
The Department of War has two meanings. Historically, it was the U.S. executive department that administered the Army from its creation on August 7, 1789 until 1947. Under the National Security Act of 1947 the War Department was split into the Department of the Army and the Department of the Air Force, which together with the Department of the Navy formed the National Military Establishment, renamed the Department of Defense in 1949. In its modern usage, "Department of War" is a revived name for that same Department of Defense: a September 5, 2025 executive order authorized "Department of War" and "Secretary of War" as secondary titles, and the department and agencies such as DARPA now use the name. Importantly, this is a naming change by executive action, not by statute, so the department is still legally established as the Department of Defense, and only an act of Congress can make "Department of War" the formal legal name. For a defense-tech founder, the practical takeaway is simple: the Department of War and the Department of Defense are the same customer, and the contract rules, compliance duties, and insurance requirements are identical regardless of which name appears.
Source: U.S. Department of Defense (defense.gov)
A September 5, 2025 executive order revived "Department of War" (last used in 1947) as a secondary title for the Department of Defense, along with "Secretary of War." The order directs the department to use these names in official contexts, but it did not change the law, so "Department of Defense" remains the statutory name unless Congress acts.
Yes. Today they refer to the same executive department. "Department of War" is the historical pre-1947 name and, since 2025, a secondary name for the Department of Defense. The older War Department (1789 to 1947) ran only the Army, whereas today the department oversees all the armed forces.
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