The P51 Mustang, a single-engine warplane fighter, although a late arrival in the Second World War, proved vital in the crucial air-war conflict in Europe. It was first envisaged in a tactical role - a low to medium level reconnaissance fighter-bomber supporting army ground operations. It did well but was rejected by RAF Fighter Command as a high-level dogfighter as being out-performed above medium levels of altitude. RAF Bomber Command had abandoned day-time raiding over Germany because of the vulnerability of its bombers to fighter attack beyond the range of escort limit range of Fighter Command Spitfires. The waiting Me 10lis and FW 190s would pounce causing huge losses. Bomber Command then continued to take the fight to Germany under cover of darkness.The US Eighth Army Air Force renewed daylight bombing with tactics of attacking in large formations of Boeing B17 Flying Fortresses with heavy machine guns for defensive cover but against experienced Luftwaffe pilots losses again mounted to unsustainable levels. The author gives a stunning picture of air crew experience in which the reader can feel personally involved. Development of the P51 continued and this must be one of the success-stories of the air-war. Rolles-Royce approved the admirable air frame and substituted the RR Merlin engine for the inadequately supercharged Alison engine. Merlin engines had been fitted in the Hawker Hurricane, Supermarine Spitfires, de Havilland Mosquito and Avro Lancaster. The result was the Mustang as a virtually unbeatable high-altitude dogfighter with large fuel tanks giving a huge radius of action. So here was a world-class strategic fighter which could protect strategic bombers to the target and home again. The P51 Mustang was the single engine fighter with strategic capability that transformed strategic bombing as a war-winning campaign in Europe. Here is the essential difference between strategy and tactics and connection with concepts of ''offensive'' and ''defensive'' and the unique role of the P51.