Powered by an Allison V-12 engine equipped with a single stage supercharger, the A-36 Apache was essentially an early model P-51 Mustang fitted with two dive brakes on each wing. Other modifications to the airframe included strengthening of the wings, movement of the bomb racks closer to the main landing gear for less wing "flexing" while the plane was taxiing, and the installation of small vent windows in the windscreen side panels. In addition, two .50 caliber machine guns were mounted in each wing, and two Browning M2 .50 cal. guns were mounted in the lower nose to fire through the propeller. Naturally, the A-36 inherited the Mustang's clean aerodynamics; but why did North American turn the P-51 into a dive-bomber? To answer this question, we must look at the Mustang's origins. In early 1940, the British asked the company to build Curtiss P-40's under license from Curtiss. Rather than building another company's design (especially one that was already considered obsolete), North American proposed building a fighter of its own. After some hesitation (the company had no fighter experience), the British agreed, and the first Mustang prototype (the NA-73X) flew on October 26, 1940. Flight tests were successful, and the British ordered 320 of the new planes, calling them Mustang I's. Interestingly, the U.S. government kept two Mustangs for itself, calling them XP-51's. Ultimately, the British received 650 Mustang I, Ia, and II's through outright purchase and Lend/Lease distribution. By the time the Lend/Lease order was placed, U.S. pilots had flown the two XP-51's and were raving about their performance. As a result, the U.S. retained 55 England – bound Mustangs for itself. The majority of these 55 airplanes were converted into to armed, high-speed reconnaissance aircraft, known as F-6's. The rest were used as high-speed ground attack airplanes, and as low altitude escort fighters. The British used their Mustang primarily in the close air support role as well.
Despite the Mustang's effectiveness as a ground-support airplane, enthusiasm by the military leaders on both sides of the Atlantic was lukewarm at best. The British, although satisfied with their Mustangs, were apprehensive about relying on a foreign aircraft. They were concerned about the availability of parts and maintenance. Hence, they focused their efforts on developing their own fighters. At the same time, the U.S. Army was already buying P-38's, P-39's, and P-40's. By 1942, there was no money in the defense budget for new fighters. It appeared that production of the Mustang was coming to an end. Fortunately, a few people recognized the Mustang's potential. One of these Mustang "visionaries" was Major General Oliver P. Echols, who was instrumental in the Army's successful retention of the 55 Lend/Lease Mustangs. General Echols noticed that there was money available in the budget for attack airplanes, and he brought this to the attention of North American's "Dutch" Kindelberger. Kindelberger, in turn, approached Army Lt. General Henry H. "Hap" Arnold with the idea of turning the P-51 into a dive-bomber, knowing that Arnold had been an early proponent of dive-bombing tactics.
Although Army doctrine held that dive-bombing was ineffective and dangerous, (because of the high dive and pull-out speeds), Arnold had managed to persuade the Army to procure a few dive bombers – the Douglas A-24, and the Vultee A-31 among them. If Arnold would go along with the idea of producing a Mustang dive – bomber, North American's production lines would be kept open. Kindelberger managed to convince Arnold that, by replacing the British armament (two 20mm cannon in each wing) with .50 cal. machine guns, and adding dive flaps, the Mustang would fill the bill as a dive-bomber. Arnold was convinced, and the first A-36 flew on September 21, 1942. Only five hundred A-36's were built. The results of flight tests conducted at Florida's Eglin Army Air Field seemed to reinforce the Army's doubts about dive-bombing, and the A-36. The A-36 dove at speeds approaching 500 mph; the brakes only reduced the speed to about 350mph. Unfortunately, one of the test airplanes crashed because it lost its wings during a vertical dive. Not surprisingly, Army officials decided that the airplane had great diving capabilities for a fighter, but dove too fast for a dive – bomber. As a result of all this, the Army restricted the plane's dive-angles to 70 degrees. In addition, the evaluators at Eglin recommended that the A-36 be used mainly as a low-altitude attack airplane, and that the dive brakes be eliminated. This last recommendation may have given rise to the oft-repeated myth that all A-36's had their dive brakes wired shut. Apparently, this recommendation was never adopted as official policy.
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The Plane That Saved The Mustang: The North American A-36 Apache