Father Mulcahy says from memory, the Mi Shebeirach, a Jewish prayer for healing.
The reason Hawkeye and Trapper are so hesitant to read Cowboy his letter is because it starts with "Dear John", which is a notorious heading for letters from spouses who are trying to tell their significant other that they want to separate. Furthermore, they become worried when they notice the letter is from Reno, which is known as the divorce capital of the world.
Hometowns: HAWKEYE: Crabapple Cove, Maine; BJ: Mill Valley, California; MARGARET: Fort Ord, California; POTTER: Hannibal, Missouri; RADAR: Ottumwa, Iowa; KLINGER: Toledo. Ohio; CHARLES: Boston, Massachusetts; BURNS: Fort Wayne, Indiana; HENRY: Bloomington, Illinois; TRAPPER John: Boston, Massachusetts; MULCAHY: Philadelphia, Pennsylvania; NURSE KELLYE: Honolulu, Hawaii; SGT RIZZO: Baton Rouge, Louisiana; Cowboy: Reno, Nevada.
Final credit for actor Joe Corey (Goldstein), who sadly died of a heart attack at age 45 in August 1972.
This episode of MASH is one of a very few that doesn't revolve around Hawkeye.