Season 3, Episode 3 (September 24, 1974). Written by Laurence Marks; Directed by Hy Averback.
Henry Blake is away in Seoul, leaving Frank Burns in charge of the 4077th [1][2]. The episode cuts across several plotlines that share a common theme: the collision between the camp's medical mission and the petty, self-serving demands of military authority.
The central thread involves a wounded North Korean prisoner brought in for treatment. Colonel Flagg arrives and orders Hawkeye to patch the man up just enough that he can be returned for execution. Hawkeye refuses to cooperate with that timetable and stalls, keeping the prisoner at the 4077th to recover [1][2]. It is the first time the show stages the prisoner-of-war-execution dilemma at length, and it sets the template Flagg will revisit in "White Gold" later that season.
Around the same time, local Korean children are stealing supplies from the camp stores, and Koreans keep showing up at the gate seeking medical attention the 4077th is not officially authorized to provide [1][2]. Hawkeye takes the side of both groups against Frank's rule-bound resistance—again, the same axis the prisoner subplot runs on.
Meanwhile, Klinger mounts another Section 8 attempt, this time by trying to go AWOL [1].
The episode is one of the earlier showcases for Colonel Flagg (Edward Winter), the paranoid Army intelligence agent who periodically descends on the 4077th to investigate suspected wrongdoing. Wikipedia's character list treats "Officer of the Day" as Flagg's second canonical appearance, after "A Smattering of Intelligence" (S2E24) [3]; if you accept the disputed reading that the similar Edward Winter character "Captain Halloran" in "Deal Me Out" (S2E13) is actually Flagg under another alias, this is the third outing. Either way, Winter is still finding the character here—already convinced that Hawkeye is up to no good, but lacking the full weight of menace he would bring to later episodes like "White Gold" and "Rally 'Round the Flagg, Boys."
McLean Stevenson does not appear in this episode; Henry's absence is what puts Frank in command in the first place [1].
The episode captures the central M*A*S*H tension in its purest form: a skilled surgeon trapped inside a system that constantly obstructs him, and an early-season willingness to let the rules win sometimes. The prisoner subplot doesn't end in triumph—Hawkeye is buying time, not delivering a verdict—and the lingering image is of a man whose best move is delay.
[1] M*A*S*H season 3 - Wikipedia [2] M*A*S*H Episode Guide - MASH4077TV [3] List of M*A*S*H characters - Wikipedia