Specifications

When the war ended, the Spitfire was the only airplane that had been in continuous production throughout the war—20,351 had rolled off the assembly lines.

Aircraft - British Spitfire (UK)

For the most part, American aerospace testing was done on American aircraft.  However, beginning with WWI, whenever the United States obtained examples of foreign aircraft - either from friendly countries through cooperative arrangements or from enemies via capture or defection- they were likely to wind up at McCook Field or Wright Field for a thorough evaluation which included flight testing if possible. 

"During WWII evaluations at Wright Field included allied aircraft like the Russian Yak-9 and the British Spitfire and Mosquito, and enemy aircraft including the German JU-88, ME-109, FW-190, ME-262, and the Japanese Zero.  The end of the war brought large numbers of captured aircraft for evaluation.  As with other test flight activities, much of the foreign aircraft evaluation moved to Muroc Air Base (later Edwards AFB) after the war, but even then the occasional foreign aircraft came to the Miami Valley for testing, as a MiG-15 (courtesy of a North Korean defector) at Patterson Field attests." (Source: Against the Wind)
 

Specifications of the British Spitfire

Aircraft Type: Fighter

Crew Size: 1

Weaponry: 8 Browning machine guns (7.7mm)

Gross Weight: 6,400 pounds (2,899 kg)

Length- 29 ft. 11 in. (9.12 m)

Height - 11 ft. 5 in. (3.48 m)

Wingspan - 36 ft. 10 in. (11.23 m)

Powerplant: 1 Rolls-Royce Merlin 45 Vee piston engine

Horsepower: 1,440 hp

Range: 470 miles (756 km)

Maximum Speed: 374 mph (602 km/hr)

Maximum Altitude: 37,000 ft (11,277 m)