Character mistake: When Henry is describing the fishing reel he bought for his girlfriend, he said, "with jeweled escarpment" actually it is a 'jeweled esCAPEment" not esCARPment. An escarpment is a long slope off a plateau. An escapement is a latch/release mechanism that you would find on a device like a fishing reel.
Factual error: In surgery Trapper John is singing Frank Sinatra's version of "I got you under my skin". Although it was written in 1936, Sinatra did not release it until 1956, after the Korean War ended. The 1936 version sung by Al Bowlly sounds nothing like the version Trapper John was singing, which was mimicking Sinatra's version.
Suggested correction: While it hadn't been released on vinyl until 1956, Sinatra had sung the song as early as 1946 on his radio show and during live shows.
The version Frank Sinatra sang on his radio show was similar to the original version used in the movie "Born to Dance" (a movie he references before singing his two songs). He didn't change it to the big band version that Trapper imitates until 1956.
Goodbye, Farewell, and Amen - S11-E16
Other mistake: How did Hawkeye Pierce, a surgeon, know how to drive a tank? It is nothing like driving a car and takes skills, training and experience that a surgeon simply would not have. He wouldn't even be able to start the engine.
Springtime - S3-E6
Other mistake: While Radar is measuring the camp, he says that last year they had 2,986 square feet, but this year they have 2,863 square feet. The square root of 2,863 is about 53.5, so unless the camp is 53 feet by 53 feet (!) his numbers are WAY off. (00:16:15)
Aid Station - S3-E19
Factual error: Mulcahy asks Hawkeye if he trusts God. Hawkeye replies "It says I should on all of my money." However, the phrase "IN GOD WE TRUST" didn't appear on American bills until 1957.
Good-Bye Radar: Part 2 - S8-E5
Other mistake: When Potter enters the Swamp, his rank insignia is placed wrongly, with the feet of the eagle pointing to the front of the collar. The feet should point toward the shoulder side of the collar, as they are the next time we see Potter.
Continuity mistake: In the office, Radar is getting ready for bed, and has taken off his shirt. When he goes to tuck in his Teddy, he suddenly has sleeves.
Factual error: When the South Korean Colonel and General are in the mess tent, their rank insignia are wrong. The insignia they are wearing are for the U.S. Army.
Suggested correction: They could have been Korean Augmentation To the United States Army (KATUSA) officers, who were Koreans drafted or volunteered into the US military to act as a liaison between Koreans and the US military. As such they wore US uniforms and rank.
Factual error: Throughout the series, there are repeated instances of "I Corps" being pronounced, "Eye Corps." Since Army corps are designated by Roman numerals, it should be pronounced, "First Corps." (I wonder how they would have pronounced "III Corps" or "XVII Corps?").
Aid Station - S3-E19
Other mistake: After Hawkeye gets back from Aid Station, Trapper is making a cup of tea. When he tries to hang the tea bag on a nail on the tent post, it unwinds and falls to the floor.
Suggested correction: This isn't a mistake, especially since we don't see it hanging back up in another continuous shot.
Continuity mistake: In early episodes, Margaret's father was dead. Later, he was alive and visited the camp. Also, in a early episode, Hawkeye writing to his father, tells him to send his love to his mother. Later, he tells Winchester his mother died when he was a child.
The Sniper - S2-E10
Continuity mistake: When Hawkeye is preparing to go for his picnic, Radar brings him some brandy from Col. Blake. There is only a small amount of brandy in the bottle, which is commented on. Radar takes a jug of martini from the still to top up the bottle, but this is not done and the jug of martini remains on top of the stove untouched. When the picnic scene takes place, the brandy bottle is now nearly full with the brandy/martini mix. (00:10:00)
Character mistake: In the opening scene, Hawkeye and Trapper are operating on a two-star general. But neither one of them or the nurse is wearing their masks. They are under their chins.
Continuity mistake: When Klinger imposes himself between Oksun Li and Crosetti, he puts his hands on his hips. When Crosetti gets up, Klinger gestures with his hands which then drop down on either side. A split-second later they're on his hips again.
The Late Captain Pierce - S4-E4
Other mistake: When Digger shows Hawkeye the copy of the death certificate, Hawkeye steps out of the shower stall and its door swings back and forth. As Hawkeye wipes his face with the towel, we can see the top of the flesh colored covering Hawkeye is wearing. (00:08:05)
Goodbye, Farewell, and Amen - S11-E16
Continuity mistake: When Hawkeye is returning to camp, he and his driver completely pass some Burma-Shave signs the other have set up to welcome him back. An ambulance bus is a few feet behind them and manages to then suddenly appear at least 30 feet behind them to smash all the signs.
Factual error: Radar's mother's boyfriend owns a Nash Metropolitan, a car that was not produced until after the end of the Korean War.
Continuity mistake: In one episode, Frank's middle initial is M, then later it's D. His full name was Franklin Delano Marion Burns.