Check out this article reproducing an Air Proving Ground test report of a pair of rocket-boosted P-51D Mustangs at RetroMechanix.com:
The project was initiated to provide "flash performance" for the Mustang in response to the appearance of German turbojet and rocket-powered fighters in late 1944. Two P-51D-25 airplanes, serial nos. 44-73099 and 44-74050, were fitted with Aerojet acid-aniline rocket motors; the exhaust of the motor can be seen just in front of the tail wheel above. Red fuming nitric acid was carried in a special tank under the port wing; an aniline-alcohol mixture was carried in a tank under the starboard wing. The accompanying gallery features 27 images reproducing the majority of the report, including several rare photos of the modified aircraft. Would make for an interesting variant to model!