Complex sentence: In 1940, MacDonald volunteered and accepted a direct commission as a first lieutenant in the Army Ordnance Corps over a year before the United States entered World War II. During the war he served in the OSS in the China-Burma-India Theater of Operations.
Split into simpler sentences: In 1940, MacDonald accepted a direct commission as a first lieutenant in the Army Ordnance Corps. During World War II, he served in the OSS in the China-Burma-India Theater of Operations.