As World War II progressed, the P-51’s performance could be bested by enemy fighters in several different flight regimes. Much of the Mustang’s slightly downward trend in performance was due to the fact that each new model had more combat equipment and extra fuel added which greatly increased weight. In an attempt to reduce weight and increase performance North American engineers came up with a completely new design built to British structural strength requirements.

The first lightweight XP-51F was hand-crafted in the NAA experimental shops, Rolls-Royce powered and flew on Feb. 14, 1944. A 1500-lb. weight reduction and a 25 mph speed increase was achieved. Part of this was the results of aero-dynamic improvements that included a longer bubble canopy, lengthened radiator scoop, smaller wheels and tires that eliminated the Mustangs “cranked” wing leading edge and a thinner wing. The next lightweight model, the XP-51G featured a five-bladed English Rotol propeller with less than satisfactory results.

Pictured is the XP-51J, the final lightweight variant and the most streamlined. Carburetor air was ducted through the main radiator scoop. The lightweights were also used for high altitude testing as shown in this painting flying 45,000’ above the greater Los Angles area.

Although no lightweights reached production, lessons learned would be applied to the ultimate Mustang – the P-51H. As a final note, when the Korean War broke out, it was not the H models that were called up but the more ‘robust’ D models!