I spotted a few punctuation errors, and there was one place where I got quite confused for a moment:
At first I thought the second part of the quote was a reply by Jones. Had to go back and parse it out. I think the easiest fix would be to drop the 'Arthur added.'"Where is the Major and his secretary?" Arthur added. "Off seeing to our lodgings while we do the real work? I spoke to the engineer and the other crew. They seemed to think that they'd have no trouble driving Jenny off the ship and into the local train depot to refuel her for the first leg of our trip."
I couldn't help noticing that, periodically, someone would report a location or condition, such as:
"We're clear of the river and back under way,"
These seemed to become repetitious, but maybe it's only me. Also, some very large expanses of distance got covered with hardly any notice or mention, such as the first leg of the trip from Georgia to the Mississippi. That jarred me a little; a bit of intervening scenery could have made the trip feel more natural, as opposed to them jumping hundreds of miles between scenes."We've finished refueling," Pickworth said. "We've taken on more water and more supplies.
Lighthearted fun: I had to laugh out loud at:
Likewise:"Yes sir," answered MacAvoy cheerfully. "We've got a full head of steam, 30,000 gallons of fuel oil, a fully-stocked dining car, 100 pounds of pipe tobacco, 50,000 rounds of ammunition, a train that walks on legs like a centipede, it's a foggy morning, and we're wearing goggles."
"Hit it, my good man! We're off!" Jones shouted, getting into the spirit of things.
It all moved quite quickly, but maybe a bit too quickly; I'd have liked for it to stretch out and relax more. That would allow for more character interaction and development. All in all, though, it does just what it's supposed to do."To the Gorge, and then beyond," agreed the Major.