Robert Gruber, who plays the bellboy, was the son of writer Frank Gruber, who wrote the screenplay and novel this film is based on.
In the flashback to Japan, Tom is wearing the shoulder patch of the U.S. Army's 40th Infantry Division. The colonel at the bar is wearing the patch of the U.S. Army's 45th Infantry Division. In addition, another soldier is wearing the patch of the Third Infantry Division. All three of those units did fight in the Korean War, and were in-country in 1951.
On the United DC-8's seats, what appears to be a speaker in the seat's headrest is actually reading lights. On the back of that rectangular unit is a table light, attendant call button, and ventilation control for the passenger behind.