The producers approached Volkswagen about being a sponsor of the show. The scenes of the pilot episode that they showed VW executives included actual war footage. One of the executives recognized one of the buildings being bombed as a VW plant and declined to sponsor the show.

Gregory Peck played General Frank Savage in the Twelve O’Clock High movie. George Nader was originally set to play the role in the tv series, but the role was eventually given to Robert Lansing.

The fictional 918th Bomb Group was based on the real 306th Bomb Group, (3×306=918).

The aircraft General Savage flies is named the “Piccadilly Lily” and the radio operator on the craft is named “Cliff”.

Four generations of Colonel Gallagher’s family were in the military.

In the show, the name of the base was Archbury. This fictional name was based on the real-life base of Alconbury, which was the wartime home of the 306th Bomb Group, the group after which the 918th was modeled.

If you have a keen ear, you'll notice that some of the music used for segues on Star Trek are also used on 12 O'clock High.

Robert Lansing was reportedly difficult to work with, which is why he was replaced by Paul Burke in the second season.

At the Primetime Emmys of 1965, 12 O'Clock High won Outstanding Individual Achievements in Entertainment – Cinematographer (William W. Spencer). The Man from U.N.C.L.E. and Bonanza were also nominated.

12 O'Clock High was the only QM Production show to not show “A QM Production” in the closing credits.