For those wondering where the term "wagons" originated, back in the horse drawn era generally all engine companies were "two-piece" companies. They were composed of the horse-drawn steam engine (or pumper) with a separate piece, known as the wagon, that carried the hose (loaded much as it is today) and most personnel but no pumps. The steamer would connect at a hydrant and the wagon usually stretch the line to the fire where the company would operate.
In modern motorized times wagons with hose capacity but no pumps were usually replaced with a second pumper, in some cases a second-line piece or in others the Engine Company's former, older pumper. Many departments did away with the two piece concept by the 1980s.
Another related use of the term "wagon" was with the Fire Patrol. I understand their rigs were referred to as wagons until the very end in 2006.
Photo of Engine 10's wagon is attached.