Season 4. Episode 1 "Welcome To Korea". At the end of the episode the new commanding officer, Colonel Sherman Potter, played by Harry Morgan is introduced. In Season 3 Episode 1 "The General Flipped at Dawn", Harry Morgan played Major General Bartford Hamilton Steele.
M*A*S*H the TV show lasted 8 yrs longer than the actual Korean War did.
Early on in this episode a scene takes place in the shower between Harry Morgan and William Christopher. Right before the scene ends William pulls the chain on the lever for the shower to turn on, but the water doesn't come on; in fact when he notices the water doesn't come on, he holds onto the chain and the lever actually comes off. You can tell by his facial expressions this was totally unexpected, but since this was the end of the scene and no further dialog was needed, it was left in.
The only episode whose name was displayed during the broadcast run (as versus on the DVDs) was the final one, "Goodbye, Farewell and Amen."
When Hawkeye is temporarily blinded, he meets a soldier, Tom Straw, whose face is covered in bandages having just been blinded in battle. He is played by Tom Sullivan, who is actually blind in real life. This is the first episode that Judy Farrell, ex-wife of Mike Farrell (B.J.), appears as Nurse Abel.
In one episode, Hawkeye says to Radar, "You're a good man, Charlie Brown", a reference to the off-Broadway show of the same name based on Charles Schultz' Peanuts characters. Because the show didn't debut until 1967, this would appear to be a mistake, but it is not. The reference was intentional, an inside joke: Gary Burghoff played the title role in that play.
During the whole series, the same short loop of background chatter is used in every OR scene. You can make out the words "Doctor, do you want me to hold that for you?" and "Irrigate this!" over and over again.
When Igor salutes Hawkeye and BJ as they enter the Post-Op, he bangs the stove, making a "Doinggg" sound. Together with the crisp parade-ground salute, it's really hilarious once you have spotted it. If you wonder whether or not it was deliberate, you can almost see Igor slipping something into his pocket as he exits.
Season 2 Episode 5 "Dear Dad ... Three". Hawkeye and Trapper tell the racist soldier the story of Dr. Charles Drew. Drew was the inventor of techniques for separating and storing blood products. He was in a bad car accident and, legend has it, died because the 'whites only' hospital refused to give him a transfusion. This is an urban myth - he did die after that accident but was treated properly at the hospital.