Cal. Veh. Code § 9106
The fees specified in this code, except fees for duplicate plates, certificates or cards, need not be paid for any vehicle of a type subject to registration under this code which is operated by the Civil Air Patrol, when the vehicle has been transferred to the Civil Air Patrol by the United States Government, or any agency thereof, if by federal regulation or directive the use of such vehicle is restricted to defined activities of the Civil Air Patrol, and if by federal regulation or directive the vehicle must be returned to the United States Government when no longer required or suited for use by the Civil Air Patrol. Such vehicles shall be registered as otherwise required under this code by the Civil Air Patrol and the Civil Air Patrol shall display a license plate or plates bearing distinguishing marks or symbols as specified in this code, which plate or plates shall be furnished by the department free of charge.
Ca. Veh. Code § 9106