Twining was an outstanding Commander of bombing operations in both the Pacific and the European Theaters. In 1942-43 he was Chief of Staff to the Commander in the South Pacific and the same year was put in command of the US 13th Air Force which was one of the most powerful air formations of the war. In this capacity he had many great successes including the conduct of the air war over Guadalcanal. In 1944 he was transferred to Italy in command of the US 15th Air Force to conduct the strategic bombing of Germany and Eastern Europe. Twining was then returned to the Pacific where he directed a force of B-29s in the bombing of Japan. A decisive man, with enormous technical knowledge, he was particularly adept at exploiting possibilities.