The P-51 story begins in 1940 when the British approached North American aviation to build a new fighter. North American agreed in January, 1940, and remarkably, by September the aircraft made its first flight. The D model, powered by a Packard-Merlin Rolls-Royce V-12 engine rated at 1490 horse power, was produced in the greatest numbers. It had a maximum speed of 437 miles per hour at 25,000 feet, and a combat range of 1000 miles. It had three 50 caliber machine guns in each wing with a service ceiling of 42,000 feet and was considered the best fighter of its time.