John Wayne and Robert Ryan managed to put aside their vast political differences while making this film, although Ryan was appalled by Wayne's support for blacklisting, extending the Korean War by launching nuclear strikes on Chinese cities, and using military force to drive the Soviets out of eastern Europe. However they later did not get along at all while filming The Longest Day (1962).
Marines got the nickname of "Leathernecks" from the fact that early uniforms had a collar made of leather which was intended to protect the throat from knife wounds.
Lynn Stalmaster (uncredited), who played Castle (the second pilot shot down, whose belongings are inspected by Kirby), acted in only 5 movies. He made his name as a casting director, having been in charge of casting for an amazing 389 films and television shows over a 67-year career, including the 1978 blockbuster, Superman. His most recent casting job was in 2017 at the age of 90. His first casting job was in 1950, the same year that Flying Leathernecks was in production.
This movie is often considered merely another assignment of Nicholas Ray's at RKO for Howard Hughes to prove his political and professional alliance during the Red Scare. A blatant pro-war movie that Hughes cared about and Ray did not, Ray disagreed with the film's politics and was said to get Robert Ryan to intentionally overact. Ryan and Ray, who were leftist liberals, constantly fought against John Wayne and Jay C. Flippen, who were conservatives and supported the Blacklist.
Robert Ryan was cast by director Nicholas Ray because he had been a boxer in college and believed that he was the only actor that could play opposite John Wayne and "kick Wayne's ass."