Complex sentence: Kelly served with the unit from 1943 until the end of the European phase of the war: returning home, he attended the School of the Museum of Fine Arts, Boston, from 1946 to 1947.
Split into simpler sentences: Kelly served with the unit from 1943 until the end of the European phase of the war. Upon returning home, he attended the School of the Museum of Fine Arts, Boston, from 1946 to 1947.