Complex sentence: Monthan enlisted in the Army as a private in 1917, was commissioned as a ground officer in 1918, and later became a pilot; he was killed in the crash of a Martin bomber in Hawaii in 1924.
Split into simpler sentences: Monthan enlisted in the Army as a private in 1917, was commissioned as a ground officer in 1918, and later became a pilot. He was killed in a crash of a Martin bomber in Hawaii in 1924.