Nothing To Fear
The biggest vehicle that Johnny had ever seen was a train, or, specifically, a locomotive. They came through Tombstone fairly regularly. Admittedly, the inside of the TARDIS was a bit wider than one of the train cars, so he'd just assumed it was the interior of a steamship, maybe even a riverboat. He hadn't made it as far east as the Mississippi River to see one for himself, though... just pictures.
He had no idea what to expect when he stepped out of the TARDIS. What little imagination he might have had been overwhelmed by the time tunnel and his recent... trips.
It was quite natural for him to look back at the vessel he'd just been in... in case he actually had a chance to return to it.
He looked at the blue police call box in puzzlement... then at the warehouse behind it.
"I don't understand," he said to the Doctor. "What happened to your ship?"
He reached out and felt around to the sides of the box, only semi-expecting to find something invisible there, though he wasn't sure if that would have been even stranger.
"Is this what they used in Denver or St. Louis?"