Famously nicknamed the Flying Tigers, the 1st American Volunteer Group (AVG) of the Chinese Air Force in 1941–1942 was composed of pilots from the United States Army (USAAF),Navy (USN), and Marine Corps (USMC), recruited under presidential authority and commanded by Claire Lee Chennault.
The group consisted of three fighter squadrons with about 20 aircraft each. It trained in Burma before the American entry into World War II with the mission of defending China against Japanese forces. Arguably, the group was a private military contractor, and for that reason the volunteers have sometimes been called mercenaries. The members of the group had lucrative contracts with salaries ranging from $250 a month for a mechanic to $750 for a squadron commander, roughly three times what they had been making in the U.S. forces.
Interesting history. At those wages (and if the internet existed) they could have almost afforded to hit up Ovadia & Sons to pick up this $235 camouflage shirt bearing their insignia.