The North American P-51 Mustang was designed for the RAF early in WW2. It entered combat service in 1942. Fitting Mustangs with the Rolls Royce Merlin engine made a good fighter into a great one, and with the addition of drop-tanks the allies had the long-range escort fighter they needed so badly. The Mustang 'B' was armed with 4 x 12.7mm machine guns, and could also carry drop-tanks or bombs. 5 so far, but many more to come: P-51B the Dominican Republic Air Force 1948. P-51B (Mustang III) of 19 Squadron RAF 1944. P-51B (Mustang III) of 112 Squadron RAF 1945. P-51B (Mustang III) of 129 Squadron RAF 1944. P-51B of the 2nd Fighter Squadron USAAF 1944.