Sentinel's first new-construction locomotive, Nº 5156, was built in July 1923. Like the railmotor design, this used the newly developed engine of the Super-Sentinel wagon, placed horizontally between the frames. This was of gauge, establishing a precedent for Sentinel of building locomotives across a range of gauges by simply changing the axles and bearings under a standard chassis. The boiler used was also the new Super-Sentinel pattern at 230 psi, with the 'spiral' firebox.
