I tried to post this last night but either it was removed or it never made it to the forum.
The link below leads to several aviation-related postal coveres I collected as a kid. Two of them are from the opening of new airmail routes. Does this happen anymore in the USA? I suspect the mail-carrying capacity of today's airliners has eliminated dedicated airmail routes, but I don't know for sure.
Two other covers may interest the military aviation buff, as they relate to the launch of America's most potent air defense missile, the IM-99B