California is the hub for AP.. The pacific side of the world
Before it all got reorganized, the hub in California was FPO (Fleet Post Office). The hub for APO was New York. That's all old stuff now.
The Joint Military Postal Activity is located in Chicago. They are the liaison to the USPS International Service Centers located in Chicago, San Francisco, Honolulu, New York City, Jersey City, and Miami.
I just wish sometimes it was faster but that cost money and we all know the military doesn't have any to spare.