During the interwar period, military theory and doctrine bifurcated, and two distinct schools of thought developed about the proper use of air power. One school, following the precepts of Italian theorist Guilio Douhet, advocated concentration on strategic bombing by heavy, self-defending "battle planes" on targets far behind the battle lines, with the intent of collapsing an enemy nation's will to continue the fight. Most British and U.S. air power advocates supported this concept.
The second school of thought, generally adhered to by the Soviet Union, France, and Germany, advocated air power in direct support to ground maneuver operations. In this vision of air power, aircraft primarily attacked targets on the front lines or behind the front, which might extend as much as 150 miles. These theorists saw air forces as working in direct support of ground forces, enabling the latter to move farther in the attack or to yield less terrain in the defense.
Each school drove aircraft design in particular directions. Thus, the United States and Great Britain came up with four-engine "strategic" bombers such as the American Boeing B-17 Flying Fortress (Douhet's self-defending "battle plane") and the British Avro Lancaster. The Germans, however, concentrated on fast fighters such as the Me-109 to secure air superiority over the battlefield for fast medium-sized dual-engine bombers such as the Heinkel He-111 and the Dornier Do-17. The Germans, having learned from U.S. Marine Corps operations, also embraced dive-bombing, developing their important single-engine Junkers Ju-87 Stuka, which could deliver its ordnance with great accuracy and proved vital during the war's early campaigns. The Luftwaffe was essentially intended for close air support, geared to ground operations.
The multiple German blitzkriegs against Poland (1939), Norway (1940), and France (1940) demonstrated the great importance of the ground-attack school of thought. Luftwaffe units, working in close coordination with advancing columns of German infantry and armor, were a key element in allowing those columns to cut through opposing forces with seeming ease. We now know that German air-to-ground coordination was far from perfect and that several German troops became casualties of friendly fire.
First with the British in fighting in eastern North Africa and then with the Americans in French North Africa, the western Allies developed their own system of close air support. Almost immediately, the Americans discovered that their own system of command and control for ground-attack operations, developed before the war, was inefficient and could not keep pace with rapidly shifting operations on the ground. Capitalizing on their great strength of being able to adapt to changed circumstances, the Americans jettisoned their own doctrine nearly wholesale and adopted a modified version of the British system. Thereafter their efficiency in ground-attack operations increased markedly.
At the same time, the Soviet air force, which had suffered heavily in the German invasion of the Soviet Union beginning in June 1941, perfected its own system of ground support aviation. The USSR developed some highly successful ground-attack fighters and fighter-bombers in the Yakovlev Yak-4 and especially the Ilyushin Il-2 Sturmovik. Flying low and employing rockets, Sturmoviks were efficient tank killers. Sturmoviks, purpose-built for the ground-attack role, were heavily armored at crucial points to protect against German antiaircraft fire. The Il-2 was perhaps the best ground-attack aircraft of the war. In testimony to its success, the Sturmovik remained in production until 1955; the Soviets produced some 36,000 of them.
Simultaneously, the western Allies began to specialize—in use if not in design—their own aircraft. Both Great Britain and the United States entered the war with credible, if not outstanding, medium bombers such as the North American B-25 Mitchell and the British Bristol Blenheim. The British added other aircraft, including the versatile De Havilland Mosquito, while the Americans produced excellent fighters in the ground-attack role, such as the Vought F4U Corsair, the twin-engine Lockheed P-38 Lightning, the Republic P-47 Thunderbolt, and the North American P-51 Mustang. The P-38, P-47, and P-51 were originally designed as bomber escorts or classic conventional pursuit planes (hence the P in the nomenclature). The P-51 Mustang, a superb aircraft, may have been the best all-around fighter of the war, but the P-38 and P-47 each had characteristics that made them more suited to lower-level work and the rigors of close air support. For the Thunderbolt, it was the fact that the aircraft could absorb significant damage and continue flying. Its air-cooled engine was less susceptible to failure from damage than was the Mustang engine, and ground-attack work generally meant taking ground fire while flying at low altitude. The Lightning had twin engines on twin booms with a pod for the pilot slung between them, and it combined decent range with the heavy punch of five .50 caliber machine guns that fired straight ahead from the central pod. (The guns of most conventional aircraft were aimed inward to a single point.) This gave it lethal accuracy; the dual air-cooled engines gave the pilot a decent chance to make it home, even if one engine was shut down. On the British side was the Hawker Typhoon, an underappreciated contender for the title of best ground-attack aircraft of the war.
The air-ground team for the western Allies in the European Theater of Operations truly came into its own in the summer of 1944 during the Allied push across France. The penultimate display of this was the complete linkage between Lieutenant General George S. Patton's Third Army, the widest-ranging and fastest-moving element of the Allied sweep across France, and Major General Elwood "Pete" Queseda's IX Tactical Fighter Command. Patton, with no forces to spare to cover his right flank, committed the security of that increasingly open and vulnerable edge wholly to the air units under Queseda's command.
Ground-attack aviation was also important in the Pacific Theater, although it was perhaps marginally less effective in jungle terrain. U.S. air power proved vital in the struggle for Guadalcanal, for example; both the Japanese and the Americans saw control of Henderson Field as the key to the campaign. Overwhelming air support proved immensely important to Allied forces in the subsequent island-hopping campaigns in the Southwest Pacific along the New Guinea coast and at Bougainville. The introduction of napalm in 1944 gave another potent weapon to close air support fighters such as the F4U Corsair—the combination was used to great effect in the Philippines, the Marianas, and on Okinawa. Ground-attack aviation, which began in World War I, came into its own in World War II.
Boyne, Walter J. Clash of Wings: World War II in the Air. New York: Simon and Schuster, 1994.; Buckley, John. Air Power in the Age of Total War. London: UCL Press, 1999.; Hallion, Richard P. Strike from the Sky: The History of Battlefield Air Attack, 1911–1945. Washington, DC: Smithsonian Institution Press, 1989.; Hughes, Thomas Alexander. Over Lord: General Pete Quesada and the Triumph of Tactical Air Power in World War II. New York: Free Press, 1995.; Murray, Williamson. Luftwaffe. Baltimore, MD: Nautical and Aviation Publishing, 1985.