I know, this thread hasn't been active for over two weeks but, when I saw the reference made on the P-38, I felt I had to speak up.
When the P-38 was first designed and built, it had the same engine and gearbox mounted on both nacelles. Like most other planes, both props rotated CLOCKWISE when viewed from the cockpit. This did, however, cause handling issues due to the "swirling" wake from the props hitting the vertical tails. To eliminate the problems this caused, the left engine was given a gearbox that reversed the prop rotation to COUNTERCLOCKWISE, thus countering the effects of the right hand prop.
When the RAF saw the P-38 and what it could do, they ordered some but, unfortunately, they ordered it with the original configuration of clockwise spinning props. The handling issues quickly resurfaced and, when combined with another issue, the plane was subsequently pulled from front line service.
The other issue the RAF had with the P-38 was its high altitude performance. Since the plane used the American made Allison 1710 rather than the Rolls Merlin 1650, engine performance dropped off above 15,000 feet much more drastically than the Merlin or German engines, even with the Lightning's Turbochargers feeding the engine's single stage Superchargers. Since most of the air combat over Europe was above 15,000 feet, the RAF felt the lack of power, at altitude, was a major liability.
The USAAC, on the other hand, fell in love with the Lightning. With the counter-rotating props and extremely long range(not equaled until the Merlin powered P-51 Mustang arrived), the Lightnings were quickly thrown into the fight as bomber escorts, "Pathfinder" bombers, photo-recon and several other tasks. In the Pacific, the Japanese A6M "Zero" was the primary fighter used by the Army and Navy for the first half of WWII. Like the Lightning, it was best below 15,000 feet and long ranged. Unlike the A6M, however, the Lightning was much faster, had armor and self sealing fuel tanks, but the biggest advantage was it could return home with one engine inoperable. So effective was the Lightning, over the Pacific, that the two highest scoring American pilots flew it.