This is both the only episode where a regular character writes to a real person, and the only episode where a character writes to a real person who was alive during the Korean Conflict. In the season five episode "Dear Sigmund", Major Freedman, who was a recurring character, wrote to the late Sigmund Freud.
The exchange between Margaret and Kim Han about whistling is quoting from the movie To Have and Have Not. It was the first on screen pairing of Humphrey Bogart and his future wife Lauren Bacall
There are many shows where a character writes to an off-stage friend or relative, but this is only one of two shows where a character, Capt. Hawkeye Pierce, writes to a real person, President Harry S. Truman.
This episode takes place during July 1952. At the beginning there's a Movietone News segment that discusses the one-year anniversary of the truce talks, and Hawkeye is upset that 365 days of talks have produced agreement only on the shape of the table, which is why he writes the letter to President Truman. Truce talks began on July 10, 1951, so the one-year anniversary would have been in July 1952.