Continuity mistake: Before The Sniper starts firing, Hawkeye is carrying the two bottles of scotch firmly gripped by the necks. A second later, he's barely holding them by the caps, in preparation to drop them.
Continuity mistake: The "KILROY" Hawkeye writes on the window as BJ looks out was in the center with his fingertip. Later, as Hawkeye looks out, the "KILROY" is now closer to the frame, and the lettering is different, a small capital A in front of it, and lines above and below it.
Dear Mildred - S4-E7
Revealing mistake: In the shot where the horse kicks in the door, there's actually two shots - a kick, a quick cut, another kick. If you look closely, you can see how the hoof of one of the horse-leg props breaks off during the first kick. The second kick is performed by one leg only. If you look really closely - and probably use the slow-motion function - you can even make out the hand of the one wielding the leg through the hole made in the first kick. (00:18:10)
Dear Mildred - S4-E7
Continuity mistake: The injured horse that Radar, BJ, and Hawkeye go after, and who's later gifted to Colonel Potter, is played by different horses.
Dear Mildred - S4-E7
Visible crew/equipment: In the scene where BJ, Hawkeye, and Radar are in the motorcade talking about the horse, Radar is talking about how he doesn't want to give away the horse. He is standing in front of some barrels and when he moves, you can see some of the crew, the horse owner, and what looks like another horse in the background for 1 second.
Dear Mildred - S4-E7
Revealing mistake: When the camera is in a close up on Dan the pilot, the sound is a chopper that is running full power, but you can tell that the main rotors are turning slowly to simulate flight.
Dear Mildred - S4-E7
Continuity mistake: When Colonel Potter's in his office finishing up his letter to Mildred, right before Margaret, Frank, and the others walk in, the things on his desk change their positions between shots - such as the paper tray moving from Potter's left to the right side of his desk.
Dear Mildred - S4-E7
Continuity mistake: In the episode when Radar gives Potter the horse, they keep referring to the horse as "he". In later episodes, the horse is a mare named Sophie.
Continuity mistake: When Margaret pins on Frank's purple heart, his scrubs are very damp with sweat. When he enters the swamp, they're practically dry. (00:03:50)
Plot hole: When the truck with the orphans arrives, Col. Potter and Nurse Cratty greet each other like one would an old friend. Being new to Korea, Col. Potter doesn't know Nurse Cratty - as becomes clear from his reaction to Hawkeye's explanation to BJ earlier (who doesn't know Nurse Cratty for the same reason, but that's not relevant for this mistake). Note that in other parts of the series Col. Potter is depicted mostly as somewhat old-fashioned and reserved towards strangers. (00:05:20)
Continuity mistake: When Hawkeye is examining the orphan who is wiggling his tongue, there are two camera angles: one of Hawkeye from the front and one of the orphan over Hawkeye's shoulder. In the first shot, the tongue depresser that Hawkeye is holding is horizontal, in the other it is vertical. This flips back and forth a couple of times. (00:06:30)
Dear Peggy - S4-E10
Character mistake: When he sees the 'P' for Protestant on Davis' chart, Col. Hollister states "A lot of your Davises are 'J's, you know" implying that Davis is a Jewish name. In fact, the ID tag code for Jewish faith was 'H' for Hebrew. (00:18:45)
Dear Peggy - S4-E10
Audio problem: As Hawkeye calls for X-rays, you can see Klinger hollering a reply through the door, but nothing is heard. (00:21:30)
Continuity mistake: After Hawkeye and Burns drive through the puddle, the mud on the colonel's face is different in the long and closeup shots. (00:02:00)
Continuity mistake: When Frank inspects the local workers, the laundry woman bends down to help the kid put away the sandwich Burns suspected of being a bomb. After the cut, she's upright again. (00:10:45)
Factual error: In the hut with BJ, Zale, and The Moose, there's a Coleman 413E stove in the background. Trouble is, that this unit didn't appear until 1954, and the Armistice ending hostilities, ending the war, was signed July 27, 1953.
Revealing mistake: When Radar walks into the supply room, he carries four or five ammunition belts around his neck. Since he stows them in The Gun bin, it has to be assumed that they are not meant to be empty. If they were only half filled each, he would still be carrying something in the area of 60-100lb. However he moves with absolutely no visible strain and tosses the belts into The Gun bin with ease. Elsewhere in the series Radar is depicted as being none too strong. Clearly the magazine pouches were stuffed with something light and the effect carrying the real weight would have on Radar was overlooked. (00:06:45)
Factual error: After Radar asks Klinger when his home movies will be ready, Max answers, "Ready whenever you are, C.B." This is the specific punch line to a joke that relates to the actual filming of Cecil B. DeMille's 1956 movie The Ten Commandments, which wasn't released until after the Korean War. (00:16:30)
Visible crew/equipment: When Margaret listens in on Frank's phone conversation with his wife, Margaret throws a chair at him and storms out of the office, and after she calls Frank a chinless chipmunk a boom mic dips into view at the top, left corner of the screen.
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).
Captain Defenestrator