When Michael is testifying before a Congressional committee, he says "...I was awarded the Navy Cross for actions in defense of my country." However, in "The Godfather", when Michael appears at his sister's wedding wearing his Marine Corps uniform, his ribbons include the Silver Star, Navy and Marine Corps Medal, and the Purple Heart--but no Navy Cross.
It might be argued that this is not a slip-up, but rather: 1)at the time of Connie's wedding, World War II had bee over for only a short time; therefore Michael's Navy Cross citation might not yet have been confirmed; or 2)Michael simply lied about his medal.