69 Years After Trinity

On this date 69 years ago — July 16, 1945 — the world was divided. Half was peaceful, and half was still at war. And an event in New Mexico changed history.

The war in Europe had been over for nine weeks, since the German surrender on May 8th. But the war in Asia and the Pacific continued and appeared likely to keep on for at least another year. Harry Truman, Winston Churchill, and Joseph Stalin were meeting at Potsdam, mostly to make plans for post-war Europe. But Truman and Churchill were also outlining surrender terms for Japan.

While there, Secretary of War Henry L. Stimson delivered a message to President Truman that said "Operated this morning. Diagnosis not complete but results seem satisfactory and already exceed expectations ... Dr. Groves pleased." This was the message that told Truman that the Trinity Test had taken place in New Mexico earlier in the day, and had been a success. As a result, Truman mentioned having an unspecified "powerful new weapon" to Stalin; presumably Churchill got more details. At the end of the conference, an ultimatum (that did not mention the new weapon) was given to Japan to surrender or meet "prompt and utter destruction".

When the Potsdam Conference began, the Allies were looking at plans for another year or more of war in the Pacific, including invasions of the Japanese home islands that would have made D-Day look small. Because of the Trinity Test (and the resulting operations), Japan surrendered — without an invasion — a little over a month after Trinity.

The Manhattan Project and its Trinity Test changed the course of the Pacific War. Today is the 69th anniversary of that change.