The 4077th MASH Officers' Club was the social center of the camp where everyone could relax after a hard day's work. The club building, a permanent structure made of corrugated iron, was donated to the camp by Major General Maynard Mitchell in the Season 2 episode "Officers Only" as a gesture of thanks after the MASH had saved the life of his son.
The Officers' Club was located on the east side of the camp, near the motor pool (see see map here). Next to it was a wooden stage, with the Commander's tent and the hospital building beyond.
The location of the Officers' Club is clearly shown in this scene from "The Price" (Season 7). Note the hospital building with the Swamp in between. To the right of the club building is a wooden stage and further to the right is the Commander's tent.
Originally, the custom of the Club was to admit officers only but a new tradition was set during the opening ceremony of the club in the episode "Officers Only" where it was decided that relatives and family of officers could also be admitted. And since Hawkeye considered everyone in the camp as his family, everyone could get in.
The decor of the Officers' Club changed as the series progressed but key features were a bar where drinks were served, a juke-box, two slot machines, a pinball machine and a piano.
The Officers' Club featured heavily in a number of episodes besides "Officers Only". In "Henry in Love" (Season 2), Henry Blake brought the girl he had met in Tokyo, Nancy Sue Parker, a former cheerleader, to the club where she performed a cheer routine to music from the jukebox. In "Your Hit Parade" (Season 6), the club became a temporary ward when the MASH suddenly had to cope with an influx of wounded. In "The Grim Reaper" (Season 6), Hawkeye decks Colonel Victor Bloodworth in the O. Club. In "The Best of Enemies", the O. Club is the scene of the bridge competition between Potter, Winchester, Margaret and B.J.
The series has a lack of continuity in "The Moon is Not Blue", where the club is temporarily shut down for not being run by official military personnel.
A view of the interior furnishings early in the series, from "Officers Only" (Season 1). There are Japanese prints or paintings on the walls. Two slot machines are to the right and on the left is a pinball machine. The piano will be there in later seasons.
The O Club has been converted into a ward in "Your Hit Parade" (Season 6). Note the Japanese paintings on the walls have been replaced with other decorations. The red and white disc is the emblem of the Eighth United States Army. Next to it is the emblem of the 69th Fighter Squadron - which never served in Korea. Note one slot machine has been moved to where the jukebox would normally be.
A better view of the jukebox from a scene in "Your Retention, Please" (Season 9). To the far right is a red poster with the silhouette of a Huey helicopter which is an anachronism.