Oppenheimer’s mood changed almost immediately after Trinity. He grew melancholy and reflective but continued to participate in discussions about ensuring the bomb’s delivery.

On August 6, the first atomic bomb exploded over the Japanese city of Hiroshima, and Oppenheimer received a congratulatory call from Groves in Washington, DC. Many at Los Alamos celebrated the news.

When a second atomic bomb exploded over Nagasaki three days later, however, the mood turned somber. At times, Oppenheimer appeared plagued by misgivings. In late August, he and Kitty spent a week at Perro Caliente to get away and recharge. When they returned to Los Alamos, however, Kitty told a friend that Oppenheimer had become depressed and that she feared for him. In October, Robert Serber and Phil Morrison reported on what they saw in Hiroshima and Nagasaki a month after the bombs. Their report deepened the sense of horror at Los Alamos. Oppenheimer lamented the retirement of Secretary of War Stimson.

Oppenheimer became a national celebrity. Los Alamos scientists organized, drafted a statement opposing the proliferation of atomic weapons, and entrusted Oppenheimer with making their case to policymakers in Washington, DC.