This was the first time M*A*S*H took the more serious tone that would be far more common in the later seasons.
When Trapper asks how long Hawkeye and Gillis have known each other, Gillis looks at his watch and says fifteen years. Hawkeye corrects hims and says, "No, longer than that, since grammar school, fourth grade." Gillis says "Fifth grade." If it was only fifteen years since then the pair would only be 25-26 years old. In the novel Hawkeye is explicitly named as 28 (which is the youngest a trained surgeon would have been at the time, without starting college prior to 18). Alan Alda was 36 and James T Callaghan 42 at the time.
On March 18, 1966 Ron Howard played Opie Taylor from "The Andy Griffith Show (1960)" who runs away from Mayberry to join the Marines in Opie Joins the Marines (1966)." But this occurred during a crossover episode of "Gomer Pyle USMC" and not The Andy Griffith Show.
The title is based on the title of the book that Corporal Gillis plans to write about his experience in Korea.