When ships were in their home ports, the naval bases provided two vehicles to ships of the frigate through cruiser size. One was a pickup truck, the use of which was controlled by either the OOD or the CDO. The other vehicle was a four-door sedan, which was controlled by the CDO or the XO. They were the land-based analogues to the Motor Whaleboat and the Captain's Gig. The vehicles were technically assigned to the local Supply Center's motor pool, which took care of maintenance. Gas was from the base gas station; the drivers would sign a sheet that gave the vehicle ID number.
Two vehicles did not begin to scratch the requirements for transportation of ships that had 250-350 people on board. Sailors and officers often had to use their personal vehicles for routine ship's business, though larger vehicles could be signed out of the motor pool for special uses.
So there was this one ship. A few sailors made it their practice to go over to Base Salvage from time to time. One of the sailors found some vehicles and he tried to start them. One old step-side pickup truck started, so he took it back to his ship. The Supply Officer had a cow, so to speak, because the ship wasn't authorized three vehicles. He pointed out that they couldn't get gas at the base gas station, because the truck's serial number was stricken.
The XO told the SuppO to close his eyes and forget that he ever saw the truck. One of the chiefs drove to the far reaches of the base and found a similar truck. He wrote down the serial number of that truck. The unofficial ship's truck was then re-numbered to match the other truck.
When it was necessary to get gas, the only risk, although tiny, was that two identically-numbered trucks would be gassing up at the same time. But since there was more than one gas station on that huge base, the risk was negligible. The driver would drive up to the pumps and fill up the truck. The supply weasel at the station would note down the truck's number and the driver would drive away.
When the ship deployed to the Med, the truck was parked out behind the barn of one of the chiefs, who lived in a rural area. A large tarp was thrown over it and staked down. After the ship returned, the truck was retrieved and put back into service.
Finally the day came when the ship was assigned to another home port. Nobody was too keen on trying to drive that old truck a thousand miles or so over the highways, so it was parked in the pier's parking lot with the keys inside of it.
 A subject for a later post.
 Salvage was where ships and commands dropped off unneeded equipment. If another unit didn't want it, then it was disposed of after a period of time.