From the handbook (Page 13):
Built by Smithy
Mobile unit - Combat - Weapon: Blast of Flame.
Large wooden barrel with swiveling nozzle. Driver sits atop a hissing steam boiler in front. The boiler provides a source of propulsion for the vehicle and pressure for the gout of flame that blasts any nearby enemies. The Fire Wagon is quick to destroy all who mock its quaintness.
Note: Fire Wagons are slow-moving, slow-turning units which however have a very agile flame throwing pipe as a weapon that can strike both flying and land/water units.