"Dear Sis" is the 14th episode of Season 7 of M*A*S*H (162nd overall), originally aired on December 18, 1978 on CBS. Written and directed by Alan Alda, it was the show's first Christmas episode since Season 1's "Dear Dad" seven years earlier [1].
The episode is structured as a letter from Father Mulcahy (William Christopher) to his sister, a nun. Mulcahy is deeply depressed, feeling he is "misused, misled, and misunderstood" at the 4077th. He recounts a series of frustrating events: in O.R., a frightened patient grabs him by the throat; he tries to collect donations for local orphans but Winchester refuses to contribute; and a wounded soldier in triage shoves Margaret and punches Mulcahy. Overwhelmed, Mulcahy punches back—then sits alone, consumed by guilt [2].
Meanwhile, Winchester (David Ogden Stiers) is miserable about spending Christmas far from his beloved Boston. At the camp Christmas party, B.J. enters through the roof dressed as Santa Claus and distributes gifts. Winchester sits alone in a corner, sulking.
Radar approaches Charles with a glass of eggnog and tells him there is a present waiting for him. Charles is skeptical, thinking it is a gag. But when he opens the gift, he discovers his old childhood toboggan cap. Radar explains:
"Yes sir. I knew you weren't happy here, so I wrote your mother and asked her to send something that would make you feel more at home here."
Radar then reveals: "Actually, it was Father Mulcahy's idea to write your mom."
Overwhelmed with gratitude, Charles rushes to Mulcahy and pulls out his bankroll. He first hands over a stack of bills, saying "Here. Buy them whatever they need." Then, in a burst of emotion, he stuffs the rest of his entire bankroll into Mulcahy's hand: "Here! Buy them whatever they DON'T need!" He delivers one of the series' most beloved speeches:
"You saved me, Father. You lowered a bucket into the well of my despair, and you raised me up to the light of day. I thank you for that."
He follows with: "I never had much use for men of the cloth, they're so... religious. But you, Father, are a credit to... your type of person" [2][3].
Radar's cow Edna goes into labor back in Iowa. Mulcahy tries to bless the calf over the phone with Radar's mother, but the calf turns out to be breech ("It's coming out backwards!"). Winchester, who had been waiting in line to call his sister in Boston, is drafted to talk Mrs. O'Reilly through the delivery. His blunt medical instructions—"You're going to have to put your hand inside the cow and turn the calf around"—leave Radar completely grossed out [2].
B.J. (Mike Farrell) also makes a memorable entrance during the Christmas party, descending through the roof dressed as Santa Claus to distribute gifts to the camp and the local orphanage children [3].
The episode closes with the entire cast singing "Dona Nobis Pacem" ("Give Us Peace") in the snow—one of the show's most iconic musical moments. David Ogden Stiers, who was classically trained and an accomplished musician, conducted the rehearsals and led the cast in learning and performing the song [3].
During the singing, Charles removes his toboggan cap, looks at it, glances at Radar, and smiles to himself. According to the MASH Historian's script analysis, this moment is not in the shooting script—it was almost certainly ad-libbed by Stiers, a perfect unscripted character moment [4].
Hawkeye then proposes a toast to Father Mulcahy: "Someone who's too modest, too utterly simple a man to know how much strength he gives us just by the decency of his life among us." The episode ends on a freeze frame with silent credits, a rare departure from the usual format [2][3].
The original script (dated October 25, 1978) had a different ending: an O.R. scene where the whole gang bickers before singing "Angels We Have Heard on High" rather than the snow scene with "Dona Nobis Pacem." Other notable changes between script and aired version include a cut poker game (Mulcahy bluffing with a pair of fours), cut lines deemed too mean-spirited toward Mulcahy, and extended dialogue scenes trimmed for time [4].
"Dear Sis" is one of only two M*A*S*H episodes notable for featuring snow on the compound, the other being "A War for All Seasons" (Season 9) [3].
In a cast/crew interview, David Ogden Stiers' mother reportedly clarified that she did not knit the toboggan cap used as a prop. The genuine emotion on Stiers' face when Charles sees the cap was entirely his acting [3].