Just happen to have an older Service Ettiquette (9/75 fifth printing of the 1963 edition) in the handy bookcase.
My comments - Naval Service (which includes the Navy and the Marine Corps, both are part of the Naval Service, saluting in the "Sea" services including the Navy, Marines, Coasties, NOAA (or whaatever it is now) and the Public Health Service is different than the Army, and the Air Force, which seems to forget it is in fact an armed service when it comes to saluting quick hide in doors its Evening Colors) is only done outdoors when covered, or unless in a duty status, which usually means covered and with a duty belt or under arms and that can be indoors. Army salutes indoors uncovered. In any case following the lead of the senior officer or enlisted present can not be wrong. A rendered should always be returned. Since a salute is a greeting by a warrior it is a gesture of mutual respect.
Book comments- O4 and down, and Warrant Officers including Midshipmen can be addressed as Mr. in a social or duty situation. May be introduced by rank and the service indicated to distinguish between Nay Lts and Captains, vice USMC, Army or AF Captains and Lts. My observations -that had evolved by the 70's and 80s that addressing by rank was not inappropriate. You are not wrong to ever address a Warrant Officer (any service) as Mister XXX. If he wants or prefers something else he'll let you know. The WO on my ship wnt by Cookie Monster in the Wardroom.
Marine Officers are commissioned as Marine Officers (generally) out of the Naval Academy, Navy ROTC and OCS. They are by law Marines at that point. By custom and tradition, most are not considered really Marines until completion of at least the Basic School, BullDog, or Boot Camp.
Its a bit of a semantical point, are they part of the "Navy", ehhh, of the "Naval Service" YES, the Commandant of the Marine Corps like the Chief of Naval Operations reports to SecNav who works for SecDef.