Rootes ' intention for the engine was to produce a new range of Commer trucks with the modern '' cab forward '' design , which required an engine low enough to mount under the driver 's cab , rather than in front of it as previously .
Rootes ' intention for the engine was to produce a new range of Commer trucks with the modern '' cab forward '' design . 
 This required an engine that was low enough to mount under the driver 's cab , rather than in front of it as previously .