Complex sentence: Chávez had hoped that he would learn skills in the Navy that would help him later when he returned to civilian life, however he soon discovered that at the time Mexican-Americans in the Navy could only work as deckhands or painters.
Split into simpler sentences: Chávez had hoped that he would learn skills in the Navy that would help him later when he returned to civilian life. However he soon discovered to his dismay that Mexican-Americans in the Navy at that time could only work as deckhands or painters.