Betty Grable was considered for the Gene Tierney role.
Robert Blake, adult actor of "Baretta" fame, plays Chandu, boy sidekick of George Montgomery.
Kunming, China was the home of The Flying Tigers.
Even though the Flying Tigers were organized as a volunteer-staffed mercenary air force earlier in 1941, they never flew in combat until December 20, 1941, two weeks after the U.S had entered World War II following the December 7th Pearl Harbor attack. So in spite of the film's plot, there was never a time they were flying in combat and the United States was still neutral in that conflict.
Even though Haoli's (Gene Teirney) surname is spelled "Young" in the credits, it likely would have been a Westernization of the Chinese surname pronounced "Yung", the Anglicized spelling for several indigenous names with that general sound. This would explain why Johnny would be confused at a seeming Western-looking, Western-dressing, Vasser educated woman turning out to be Eurasian. And even if the family surname had been Westernized for Haoli, it is highly unlikely her very refined, clearly Chinese, father would have changed the spelling of his to "Dr. Young" from "Dr. Yung".