If everyone has a chance, and you can get your hands on a copy, read Martin Caidin's book, P-38: The Fork Tailed Devil. Tons of stuff in this book relating to development, testing, combat and pilot interviews.
The RAF ordered the P-38 with the Allison engines. They wanted to get the turbochargers but the US Gov't wouldn't allow it. They needed the equipment for themselves. Consequently, the RAF received a few P-38's with non-turbocharged engines and non-handed propellers. They were dismayed by the performance. They cancelled the contract. But they did give the aircraft the name "Lightning". It stuck.
qmeister...you're correct in your statements about the Mustang. The British Purchasing Commission wanted North American to build the P-40 under licence. Edgar Schmeud and James "Dutch" Kindelberger argued they could produce a better fighter than the P-40. The B.P.C. allowed North American the opportunity to design a new aircraft with the stipulation that "The NA-73 prototype was to be ready in the time it would have taken to North American to tool up for P-40 production, namely 120 days and the cost per aircraft was not to exceed $50,000." - Great American Aricraft of WWII - Bison Books
The airframe was completed in 117 - due to alot of copycatting of systems etc, from the AT-6 to the Mustang - days but the marriage to the Allison engine didn't take place until October 1940. Testing was done by the RAF with the Allison engine and the aircraft wouldn't outperform the Bf-109 at altitude. In early 1942, one of the RAF test pilots had the idea to marry the Merlin to the Mustang airframe. They did so, resulting in the P-51B, and the rest is history.