Cannons, ballistae and trebuchets for the siege. Wagons, ships and trains for the haul. Every one is built by a town's artisan, flies its nation's flag, and is worth fighting over.
Nobody crafts an engine. Each one is a town's work: four parts, made one order at a time by its artisan, from materials other towns make. A Locomotive is made the same way, in one piece.
Three engines, each with its own look and its own job: the cannon, the ballista and the trebuchet. Find out which suits yours.
The haul by road. A covered wagon pulled by a horse, a donkey or a mule, with a bed full of goods and room for two in the back.
The haul by sea, and the fight on it. A small open hull with one mast and a square sail, a helmsman at the stern and a bolt thrower at the bow.
A train is a chain of minecarts pulled by an engine: a plain furnace cart, or a Locomotive built by a town's artisan. Couple them with chains, in order, behind the engine.
Example: Locomotive → Cart → Cart → Cart
A Locomotive loads and unloads chunks as it moves. Its trains can cross the world without anyone there to keep the chunks awake. A furnace cart's train only runs where somebody is, and waits at the edge until they come.
Laying track is no longer an iron-mine money pit.
Artisan materials, engine parts and Locomotives are heavy. You walk slowly carrying them, and nobody rides anything with them in their pockets. They travel in storage.
Every siege engine, wagon and ship belongs to the nation of whoever set it down, and flies its flag in that nation's colour.