557th Field Artillery Battalion
(Source: Bob Boberg, 557th FAM Bn)
Erector Wreck (rear view) The tires are huge and each wheel is driven by a DC motor. You can see the motor on the bottom rear wheel. The driver uses toggle switches to steer and a potentiometer for speed control. Rear wheels can turn right or left just like the front ones. Thus bouncing along narrow German roads was quite a balancing act.    
Erector Wreck.  Field problem becomes a problem when operator loses control of the erector. Fortunately he had only minor injuries and equipment damage was negligible.