Season 11, Episode 15 (February 21, 1983). Written by Dan Wilcox & Thad Mumford; Directed by Burt Metcalfe.
This penultimate episode (the second-to-last episode of the entire series) centers on Margaret's idea to create a time capsule for the 4077th, inspired by a newspaper story about a time capsule being buried in the cornerstone of a new Los Angeles skyscraper [1].
Margaret collects official military items: a nurse's manual and an Army field manual. Hawkeye initially mocks the idea but then decides to create his own "unofficial" time capsule with personal items. The two clash until a dramatic subplot unfolds: a helicopter pilot, Lt. Brannum, delivers a wounded soldier (Corporal Stoddard) after being shot by snipers. The bullet hit the helicopter's fan belt, forcing Brannum to fly in 200-yard hops—he'd land, walk ahead to find a safe clearing, walk back, fly to the new spot, wait for the engine to cool down, and repeat. At nightfall, he kept Stoddard warm with a blanket until dawn.
Remarkably, Brannum never mentioned his heroic efforts—he simply got a new fan belt and flew away. When Hawkeye learns the story, he adds the broken fan belt to the time capsule: "The pilot's heroism is something that deserves to be remembered in 100 years."
Other items added to the capsule:
The episode also introduces Soon-Lee, Klinger's future wife, and features the famous dummy hand grenade prank between Rizzo and Winchester. It serves as a beautiful setup for the series finale.