A unique one I just came across. I didn't even realize airmail stamps were precanceled and most certainly not one that goes as far back as a C2.

The city name is somewhat smeared; I think it may be Gaithersburg, MD, but not sure. Anyone have any other ideas?
I'd also be interested to know if this stamp, as a precancel, commands a different value than an unprecanceled C2.
Thanks for looking.