Military Staff and Command Cars are used for light transportation duties for senior officers and their communications. Some models are based on civilian automobiles while others are based on tactical trucks, depending on combat or non-combat missions. During and after WW II the military jeep (and later the HMMWV) replaced many of these staff car or command vehicles.
The September 1943 War Department manual TM 9-2800 ("Standard Military Motor Vehicles") lists two 5-Passenger 4x2 Sedan models:
• Light: Manufactured by Chevrolet, Ford, Plymouth
• Heavy: Manufactured by Buick, Packard
These were civilian cars -- not built to full military specs -- just stripped of chrome, painted OD and maybe a few cosmetic changes to lights or other features. Other regular passenger vehicles were routinely purchased in small quantities, not standardized.
US Army Staff Car, Casablanca, Morocco, January 1943