July 21, 1945

Little Boy

Atomic-strike directive issued for attacks on Japanese cities

The famous order to use the bomb does not carry Harry Truman's signature — and his own presidential library says no explicit written use order from him is known.

25 July 1945: the directive to Spaatz

The operational order came on 25 July 1945 — not the listed 21 July, a day whose records concern coded weapon-readiness cables and Stimson's refusal to restore Kyoto to the target list. The directive to General Carl Spaatz authorized the 509th Composite Group to attack Hiroshima, Kokura, Niigata or Nagasaki after about 3 August, as weather permitted.

It was signed by General Thomas T. Handy, by direction and with the approval of Secretary of War Henry Stimson and Army Chief of Staff George C. Marshall. The surviving order was not signed by Truman.

Where the president appears in the record

Truman's 25 July diary records that he told Stimson to use the weapon against military objectives and soldiers and sailors, avoiding the old and new capitals. But the Truman Library states that no known written record contains an explicit order from him to use atomic weapons against Japan; it identifies his 31 July authorization to release the post-strike statement as the closest written document and an implied final authorization.

Historians dispute the tidy single-presidential-decision narrative: military planning already assumed use, and authority accumulated through discussions, targeting decisions and operational orders. Officials' July cables disguised the bomb as a 'patient' approaching its 'final operation.'

What the directive set in motion

Spaatz and the 509th now held authority to conduct the first strike when weather and weapon readiness permitted — and the directive contemplated additional atomic attacks without a new presidential authorization for each bomb.

The Little Boy combat unit, L-11, was assembled by a team on Tinian led by Francis Birch and completed by the end of July. It was dropped on Hiroshima on 6 August.

Sources

Researched 23 Aug 2026 7 sources 3 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at 1945-07-25.

What the sources leave uncertain

July 21 is not supported as the date Truman approved a use order. Cables that day concerned weapon readiness and Stimson's refusal to restore Kyoto to the target list.
July 25 is conventionally treated as the decision or approval date because the operational directive was issued and Truman recorded his instructions that day.
The documentary record does not contain an explicit use order signed by Truman. The Truman Library identifies his July 31 authorization to release the post-strike statement as the closest written document and an implied final authorization.
Historians dispute the tidy “single presidential decision” narrative because military planning already assumed use and authority accumulated through discussions, targeting decisions and operational orders.