How the War Department became the Department of Defense – and back again

This article appeared in History of War magazine issue 153.

In September 2025 President Donald Trump signed an executive order renaming the Department of Defense to the 'Department of War', reverting to the original name established during the Revolutionary War. While such a change would officially require Congressional approval, the president cited a tradition of military strength and preparedness as essential to US national security.

"The Founders chose this name to signal our strength and resolve to the world," the order declared. "The name 'Department of War', more than the current 'Department of Defense', ensures peace through strength as it demonstrates our ability and willingness to fight and win wars on behalf of our nation at a moment's notice, not just to defend."

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The department originally underwent a rebrand during a radical reorganisation of the US military after the end of the Second World War.

As the free world continued to count the cost the war, the most devastating armed conflict in human history, and the early vestiges of the Cold War loomed, President Harry Truman told the American people of his intent to reshape the US military establishment.

In the autumn of 1945 he declared: "I stated that I would communicate with Congress from time to time during the current session with respect to a comprehensive and continuous program of national security. I pointed out the necessity of making timely preparation for the nation's long-range security now – while we are still mindful of what it has cost us in this war to be unprepared."

Among Truman's priorities were a reorganisation of the American armed forces hierarchy to achieve efficiency, co-ordination and unity of command while reinforcing the venerable concept of civilian control of the military.

In December 1945, Truman added: "I recommend that the Congress adopt legislation combining the War and Navy Departments into one single Department of National Defense. Such unification is another essential step – along with universal training – in the development of a comprehensive and continuous program for our future safety and for the peace and security of the world."

The National Security Act of 1947 did in fact create the National Military Establishment (NME) with a framework that separated the US Air Force from control of the US Army and established the position of Secretary of Defense.

This new cabinet post would ostensibly supervise the subordinate offices of the individual branch secretaries. The incumbent was required to be a civilian or to have been retired from the military for at least ten years. This second proviso was later modified to seven years.

Another significant component of the 1947 act was the establishment of the Joint Chiefs of Staff, composed of high-ranking military officers, the Central Intelligence Agency (preceded by the Office of Strategic Services, or OSS) and the National Security Council, an advisory body for the president in consideration of domestic, foreign and military policy.

Two years later the NME was formally renamed the Department of Defense. The entire executive initiative had been prompted not only by the command challenges of the Second World War but also in preparation for a potential war with the Soviet Union. Truman's perspective demanded an enhanced national military preparedness and response capability.

While the change of designation from War Department to National Military Establishment and then Department of Defense might be construed at first glance as an effort to quell the connotation of belligerence held with the word 'war', it was in fact necessary to differentiate the new structure from the previous alignment that had endured in various iterations since the 18th century.

Some sources claim that the change from NME to Department of Defense was necessary to eliminate the negative sound when the acronym was pronounced aloud. It simply sounded too much like 'enemy'.

The War Department had been created on 7 August 1789 during the first session of the Congress in the administration of President George Washington. Its purpose was clear: replacing the Board of War and Ordnance that had been created in the midst of the American Revolution in 1776.

The War Department was initially also known as the War Office in a nod to the British influence in North America. The fledgling US Navy was given a separate cabinet post in 1798 and encompassed the command of the US Marine Corps.

Therefore the National Security Act of 1947 effectively separated the Department of the Army from the Department of War and created the Department of the Air Force as a separate branch of the military.

The amended National Security Act, which Truman signed on 10 August 1949, brought the secretaries of the Army, Navy and Air Force directly under the Secretary of Defense and established the post of chairman of the Joint Chiefs of Staff.

The president explained that the revisions constituted a "unification… increased efficiency and economy and greater coordination of our military forces".

In fact, some observers conclude that the comprehensive restructuring fostered an unprecedented era of inter-service rivalry as exemplified in the competition between the Air Force and Navy as the primary custodian and potential deliverer of the American nuclear weapons arsenal during the burgeoning years of the Cold War.

However, such a rivalry may well have been unavoidable and the effectiveness of the realignment remains the subject of debate as it continues to function today.

This article originally appeared in History of War magazine issue 153. Click here to subscribe to the magazine and save on the cover price!