Britain supported the use of atomic bombs by the United States against Japan in World War II about a month before the first one was dropped on Hiroshima, documents recently declassified by the U.S. National Archives and Records Administration showed.

The documents illustrate Britain’s involvement in the United States’ decision to carry out the A-bombings of Hiroshima and Nagasaki in August 1945, something not widely known in Japan.

The British government officially expressed its support for using the new weapon against Japan at the Combined Policy Committee meeting in Washington on July 4, 1945, on the development and control of nuclear energy. Britain referred to atomic bombs as Tube Alloys, a codename it used for wartime research on nuclear weapons that was also used to refer to plutonium.

According to the declassified minutes, British Field Marshal Sir Henry Wilson told the meeting chaired by U.S. Secretary of War Henry Stimson that the British government “concurred in the use of the T.A. weapon against Japan.”

“The Governments of the United Kingdom and the United States had agreed that T.A. weapons should be used by the United States against Japan, the agreement of the British Government having been communicated” by Wilson, the minutes said.

The committee was established based on the Quebec Agreement made in August 1943 by the United States, Britain and Canada on coordinated development of atomic weapons.

Britain’s official agreement on the use of atomic bombs came after U.S. President Franklin Roosevelt and British Prime Minister Winston Churchill agreed at their September 1944 meeting in New York that an atomic bomb might be used against Japan when it was developed.

Shortly after the July 1945 committee meeting, the United States conducted the first atomic bomb test in New Mexico.