Cecil/WV,
Here is the answer to your question: "What did GM and Chrysler build for the war?"
GM built Cadillac engines used in tracked vehicles and also built many tens of thousands of the famous GMC Two and Half Ton Truck with various beds (Dump truck, open truck; Fuel Truck, water truck, etc.) and the famous DUKW-353 or better known as "Ducks" amphibious truck. GM built the 6-71 Diesel engine for the M4A5 tank.
Trucks used for loading bombs on US aircraft were built by GMC (GMC M-6 Bomb Service Truck). GMC also built Airfield Crash Trucks and communication radio trucks. US Army used both Ford and Chevrolet Staff cars based on standard sedans. The GMC Suburban Carry-all was also in the US motor pool. GM made the M4A2 tank and the M5 tank with Cadillac engine. GM also made the Allison V-1710 V-12 aircraft engine used to power the P-40, P-39 and the famous P-38.
Chrysler made engines for the M4A4 Medium Tank and the M3A4 tank; Dodge made the famous "WC" series of vehicles: the WC-54 Ambulance; the WC-51 Weapons Carrier; the WC-56 Command Car, WC-53 CarryAll, etc. These morphed into the famous "Power Wagon" series that we are all familiar with.
There are actual books written about all the vehicles that GMC made for just the US Army (GMC TRUCKS AT WAR). There is also a book treating the contribution of Chevrolet (CHEVROLET TRUCKS -- Vehicles for Victory).
And you didn't ask, but Packard made the Merlin V-12 engines (under license) for the famous P-51 Mustang.
TonyM.
