Was the UW fight song featured in an episode of M*A*S*H?

Affirmative! In the season three finale, titled “Abyssinia, Henry,” Trapper and Hawkeye are working on a patient when Trapper asks Hawkeye to guess the song that he’s humming. (Hawkeye incorrectly guesses “Avalon” before correctly guessing “In a Little Spanish Town”.) Father Mulcahy chimes in with a tune, which Trapper quickly guesses to be “On, Wisconsin.” Father Mulcahy corrects him, saying it was the hymn “Oh, Shepherd, Guide Thy Flock.” Radar then enters the operating room with news that Lieutenant Colonel Henry Blake, who’s also working on a patient, has officially been discharged. The room erupts in congratulations. Father Mulcahy tries to start a celebratory singing of the hymn from earlier, but only gets so far as “Oh, Shepherd —” before Hawkeye and Trapper take it away: “— on, Wisconsin, fight right through that line!” Fans of the show likely know how the episode ends: Radar enters the operating room once again, this time to deliver the news that Lt. Col. Blake’s plane had been shot down over the Sea of Japan. This time, the only sound in the room is the metallic clinking of surgical instruments as the doctors continue to work through their shock. The episode aired on March 18, 1975, making this month the 50th anniversary of both the UW’s debut on, and Lt. Col. Blake’s emotional departure, from one of network television’s most beloved shows.