Nice work on the cannons Larry. You've captured the look really well. Of course for the prototype, to camouflage something was easy, as everything was black & white.
Interesting movie. The site says the Lance Corporal is a brakeman, but I think he's the driver and the wheel is the loco's throttle.
Here is a picture of a 20 HP simplex that shows the controls. It was a one man operation. Note the peddles on the floor and the wheel. Not sure on the exact name of the operators.