Short Stiling Mk.II
Before WWII, Britain had started setting up shadow factories in Canada, to produce aircraft beyond the range of a future European war and succesful plants had been setup producing Hurricanes, Hampdens and other types. With the destruction of the Supermarine 316/317/318 programme and the serious damage to the Stirling production, this programme was vindicated early in the Battle of Britain.
Initial Stirling production was also slowed by engine availability, as the Bristol Hercules engines were prioritised for Beaufighters, and so an alternate engine was considered for the Stirling - the US Wright R-2600. Three Mk.I aircraft were modified with the American engines in 1941, to become the prototypes of the new Mk.II. Production was to be undertaken in Canada as well as the UK, and a contract was placed for 140 Canadian built aircraft. The only other major change to the Mk.I was the addition of a matched pair of Boulton Paul dorsal and ventral turrets, with the dorsal being the new Type H, and the ventral being the new Type O cannon turrets. While this new turret set was trialed at scale on the S.31 mini-Stirling they were eventually dropped and never fitted operationally.
The Wright engines provided no advantage for the Mk.II, and the engine supply issue was resolved. Meanwhile Avro had developed the Lancaster, and this new bomber design was considered a better choice for Canadian construction. And so the Stirling Mk.II was cancelled.