Salutes are not mandatory on the driver of a vehicle, whether moving or idling at the curb, for the reason that the operator is presumed to need both hands for driving. Salutes are not exchanged between moving vehicles, between moving and halted vehicles, or between persons walking and persons riding in official cars except when it is obvious that the passenger is a senior, or when it is required as part of a ceremony. Official vehicles carrying general officers or flag officers will be clearly marked outside, and will be saluted. A salute is exchanged between persons in a parked vehicle and persons walking, unless the car is a bus or taxi. When two boats pass each other, the senior officer in each boat salutes without rising. Aside from saluting, there are certain other customs that govern conduct around official vehicles. Since the place of honor is on the right, the junior not only walks on the left, but rides there as well. In entering a car, the junior enters first, followed by other members of the party in inverse order of rank, each seating himself so that the senior may take position on the right side. In leaving the car, the senior debarks first. However, if following this general procedure would necessitate any member of the party climbing over another, or in any other way cause an awkward situation, the senior may enter first and alight last. The same rules govern for boarding and leaving small boats, except that the junior rides forward and the senior aft. In boarding aircraft with a single hatch, the pilot enters first, followed by the copilot and other members of the crew. With the crew in place, other passengers enter according to rank, the senior first; he takes the seat of his choice if the aircraft is equipped with seats. In either transport or tactical aircraft, the senior officers generally ride as far forward as possible. In leaving the aircraft, the aircrew who handle deplaning normally leave first, followed by passengers in order of seniority. The long association of the Air Force with the Army precludes any large body of custom and tradition that can be called peculiarly Air Force in origin or usage. In time undoubtedly a considerable body of distinctive official and social courtesies will grow, but at present most of the official and unofficial usages given here for the Army are understood to be applicable to the Air Force as well, and will be so treated. The hand salute is required on all military installations and in occupied territories, whether on or off duty; in all official greeting in the line of duty both on and off the base; for ceremonial occasions; and in honoring the National Anthem, or color, or distinguished persons.