Book - Children and Adults - Book 1 of the Acorn Squadron Chronicles - "Earning Their Wings"

In this book, the U. S. Government has been secretly experimenting with genetic modifications in animals to create a super weapon:  a spy incapable of detection who can gather intel in any location.  Altered to be able to understand human languages and communicate via computer devices with their human counterparts, the experiments involving highly intelligent Eurasian red squirrels are a scientific success.  After repeated drone failures compromise the safety of military actions, the Pentagon recruits these modified squirrels to salvage an expensive black-ops mission.

In the tradition of the Navajo Code Talkers, the Air Force initiates Project Oaktree to train these new recruits to fly small aircraft in order to determine their qualifications for low altitude drone flight operations in the Middle East over hostile territory.  These flying squirrels turn out to be more than the Pentagon could have hoped.  Join Bushtail and the Air Force's new 999th Squadron of tiny pilots as their take flight in their first adventure to earn their wings.