As Richard Dix tries to wave down Robert Armstrong following the plane's sabotage by Von Stroheim, during the back and forth banter Armstrong's character clearly flips his middle finger or "the bird" to Dix, and with a smile on his face.
When Erich von Stroheim was first offered the part of the mad director, the character was called "Erich von Stroheim." Understandably upset at being asked to play himself as a homicidal maniac, Stroheim agreed to do the film only if the character's name were changed.
"The Lost Squadron" was begun when William LeBaron was still production chief at RKO. When he was fired, his replacement, David O. Selznick, took over the project as a personal production, fired director Paul Sloane and replaced him with George Archainbaud, and increased the film's budget to include more spectacular action sequences.
The trivia item below may give away important plot points.
Having been a stunt man in his early years in films, Erich von Stroheim refused to use a stunt double for the scene in which he is shot and falls down stairs. In taking the fall himself, he broke three ribs.