Flying Tiger Line (name distinguishes the airline from the military group Flying Tigers) was one of the last survivors of carriers formed immediately after WW2 by those who had spent the war together and bought surplus aircraft to carry on flying commercially.
Based in Los Angeles, their main focus, like many large commercial freight carriers in the US, was contract work for the military. They did internal US operations and transpacific. The US military started requiring their operators to have a proportion of civilian work so they were not over-dependent on the military side, and FTL was one of the few who built up scheduled operations in addition to charter and contract work.
In the days of tightly regulated route licences FTL dominated cargo schedules across the Pacific, and Seaboard the Atlantic; the two had been allowed little overlap in their operations. In 1980 FTL bought out Seaboard and that's when they started appearing over here extensively as well. Federal Express bought out FTL in 1990; they had done a lot of contract work for FedEx in the years leading up to that, and it gave FedEx access to scheduled freight operations to Asia and Europe.
FTL ordered a large fleet of new DC8-63F freighters for rapid delivery in the late 1960s for the extensive work they were picking up to/from Vietnam. Douglas had over-committed on delivery to them, fell behind, and the resulting compensation etc was a significant part of Douglas's financial fall from grace and their acquisition by McDonnell.
The Budd Conestoga that FTL started with was built of stainess steel. Budd were a pioneer with this material, starting with auto bodies for Detroit manufacturers and moving on to railway vehicles. The widespread use of unpainted, polished stainless railway cars, even nowadays, in the US (little used elsewhere) is all down to Budd, from their factory in Philadelphia. They were more successful with railway vehicles than with aircraft.