Question: A number of times it is mentioned that the outfit is unarmed, yet several times, Frank has a rifle, or a pistol, and once Klinger had a grenade, and the guards and Klinger, while on sentry duty, has a rifle. Was this standard, or is this a mistake?
Answer: Even an Army field hospital would have SOME weapons for self-defense if the enemy attacked. What's meant is that it's not a combat outfit, and therefore wouldn't have enough weapons to actually attack anyone. (It's also mentioned a few times that the Officer of the Watch is supposed to carry a pistol at all times, but Hawkeye refuses to do it when he's in charge and Colonels Blake and Potter don't enforce the rule).
Answer: The Geneva Convention allows even doctors to carry a sidearm to be used in their self defense or the defense of their patients, however it is rare to do so.
Answer: As an old medical unit staffer, my experience is that med units have combat units assigned to defend them. Usually it was marines.
Answer: My old doctor (now deceased) served in Korea during the War. He was required to carry a sidearm anytime he was not in the hospital.
Question: Why was the song "My Blue Heaven" used so much in the first season?
Answer: The copyright information provided in the answer is wrong. Although there's a lot more to it, works published before 1978 are protected for 95 years (28 years for the initial term and 67 for the renewal term). "My Blue Heaven"'s copyrights were renewed in 1953 and 1957. Works published after 1977 are protected for the life of the artist plus 70 years. It should be noted that the movie "My Blue Heaven", starring Betty Grable, came out in Dec 1950 in which the song was sung during the credits, which would have been during the Korean War (not that I'm saying that's the reason for its use).
Answer: My guess is because Fats Domino's version was #17 on Billboard's charts for 1957. It helps identify the time period. And, I think, at the time copyright laws only protected material for 25 years after release so the song was free to use. Now, material is protected for 75 years.
The Korean War was fought between 1950-53. The song didn't exist yet.
Question: Why do the helicopters fly backwards? Is that just a filming mistake or did they do it for a reason?
Chosen answer: The helicopters aren't flying backwards, they are simply not moving through the camera view as fast as the camera is moving.
Answer: It is actually Cencompac for Central Command of the Pacific. It is like the headquarters for all military activity in the Pacific Region (Japan, Korea, Okinawa, etc. The newer version of that is United States Pacific Command (USPACOM).
EMTurbo
And the abbreviations were used mainly by the Navy. Especially CENCOMPAC.
Https://en.wikipedia.org/wiki/United_States_Indo-Pacific_Command.