The Heisler Geared Locomotives.
Above: The Heisler had a V-2 engine slung under the boiler, driving fore-and-aft shafts on the centre-line.
One cylinder head is visible below the steam (rearmost) dome.
Above: Another Heisler at rest. It is clear that the V-2 engine configuration limits the boiler diameter. The steam supply pipe from the steam dome to the cylinder is clearly visible. The pipe running forwards presumably carries the exhaust to the blastpipe in the smokebox.
Above: Side drawing of a Heisler. The centre shafts running to forward and back bogies are visible below the boiler.