Complex sentence: During World War II (1939--45), he enlisted in the Army at Fort Knox, Kentucky, and spent most of the war as a tank-warfare instructor at Fort Campbell, Kentucky and later at West Point, New York.
Split into simpler sentences: During World War II (1939--45), he enlisted in the Army at Fort Knox, Kentucky. He spent most of the war as a tank-warfare instructor, stationed at Fort Campbell, Kentucky and later at West Point, New York.