 The higher the grade, the higher the rank of the officer.For example, an Army, Air Force, or Marine captain is equivalent in rank, responsibilities, and grade to a Navy or Coast Guard lieutenant, all of which are of the third officer grade, or O-3.Similarly, a Navy or Coast Guard captain is equivalent in rank, responsibilities, and grade to an Army, Air Force, or Marine colonel, all of which are of the sixth officer grade, or O-6.