Boeing XB-38 powered by Allison V-1710V engines A rough comparison would be: Inline - 526 kph - 5300km range Radial - 461 kph - 6000km range Was speed sacrificed for range? How would American aircraft have gone if powered by inline engines? Specifically the Merlin range? The US and Japan struggled with designing a good inline engine, one that could compete with the radials...Whilst Germany and in particular Britain designed excellent inline engines. Some of the most lauded aircraft of WW2 - Mustang, Spitfire, Lancaster, Mosquito and Hurricane were powered by this engine. How much of their success was the aircraft and how much do all these aircraft owe their reputations to the Merlin? The US correctly thought that the radial was more reliable than the inline...this was in the 30s when inline engines hadn't matured as a technology...but by WW2 this was no longer the case. Why wasn't the Merlin phased into production for all aircraft? Does politics rear its ugly head again here? I read some reasons, but none that were insurmountable... The radial is air cooled, which is reliable once airborne (but a problem sitting on the tarmac). The inline had a reasonably heavy cooling system that could break down...one rarely hears of over heating radials in flight, but not so for the Merlin inline. So what is the benefit of a radial...it was comparatively easier to build than an inline...but again, not an argument that means much to me given the production might of the US and UK... So...Do these aircraft owe their reputations to the inline/Merlin? How would the air war have panned out if more aircraft, particularly multi engined aircraft been fitted up with inlines? Some British bombers fitted radials, then inlines, then back to radials...showing that it could be done.