Here's a link to an old thread at the US Militaria Forum that discusses a similar cap. It appears that Derby was a Louisville, KY company and produced the cap discussed in the thread which came from a 1960's Air Force vet. There's some additional info on Derby, including that they did manufacture some headgear for the US military:
http://www.usmilitariaforum.com/foru...af/?hl=ballcap