The U.S. Army Air Service had no combat aircraft when the United States declared war on Germany in April 1917, nor was it possible for the fragmented American aircraft industry to provide any. Arrangements were made for the Air Service to acquire British, French, and Italian aircraft, and for American industry to build selected European types. The principal bombers chosen were the French Breguet‐14, the Italian Caproni CA‐33, and the British Airco DH‐4 and Handley Page 0/100. Plans were made to have the British and Italian aircraft built in the United States, but only the DH‐4 went into quantity production before the end of the war.
American airmen gained most of their bombardment experience in World War I in Brequet‐14s and DH‐4s. These single‐engined, two‐seat biplanes were of limited range and carrying capacity, but they were used to some effect against battlefield targets, and close behind the front lines, against supply centers and troop concentrations. Most of the operations were carried out in daylight, sometimes at low level, and both enemy fighter aircraft and ground fire caused high losses. A few Americans also experienced “strategic” bombing with the Italians, flying Capronis against targets deep inside Austrian territory. Given the primitive navigation and bombing equipment, and the fact that they were bombing from 12,000 feet or higher, in open cockpits without oxygen, it is hardly surprising that the crews had difficulty in finding, never mind hitting, their targets.
In 1917, Brig. Gen. Billy Mitchell, who rose to command the combat aircraft of the American Expeditionary Force, met and was strongly influenced by Britain's Maj. Gen. Hugh Trenchard, one of the foremost prophets of strategic airpower. Trenchard's views on the use of large numbers of heavy bombers against targets deep inside enemy territory had a marked effect on Mitchell.
The United States began its pursuit of a strategic capability in 1917 by asking the Martin Company to develop a heavy bomber. The best of the Martin series was the MB‐2, but with a top speed of only 100 mph and a range of not much more than 500 miles, it was a long way from meeting Mitchell's expectations. However, it did serve as the instrument for his dramatic airpower demonstration in 1921, during his tenure as Assistant Chief of the Air Service. Undeterred by scathing criticism, particularly from the U.S. Navy, Mitchell's MB‐2s conducted several bombing trials against warships, concluding with the spectacular destruction of two battleships, the old German Ostfriesland and the obsolete USS Alabama.
Another disappointment for Mitchell was the Barling Bomber, a massive American triplane that flew in 1923 and managed to lift over 6,000 pounds of bombs; but with such a load its top speed was just 95 mph, its range only 170 miles, and it proved incapable of climbing over the Appalachians. Technology had not caught up with ideas and the intended “superbomber” was scrapped.
The first significant steps on the road to a U.S. strategic air force were taken with the appearance of Boeing's YB‐9, a single‐engine, all‐metal monoplane, in 1931. Within a year, the YB‐9 was overshadowed by the Martin B‐10, a twin‐engine, all‐metal monoplane with retractable undercarriage, with the added features of internal bomb stowage, enclosed crew positions, wing flaps, wheel brakes, and variable pitch propellers. With a top speed of over 200 mph, the B‐10 could outstrip most fighters of the day, it could reach 25,000 feet, and its range with 1,000 pounds of bombs was 700 miles. It was “one of the most significant advances in the history of military aircraft.” Encouraged by its experience with the B‐10, the Army Air Corps pursued its ideal of a truly strategic bomber. In 1934, Boeing was awarded a contract for a “superbomber” with a 5,000‐mile range, a top speed of at least 200 mph, and a payload of 2,000 pounds. Produced as the XB‐15, engines of sufficient power were not available for the monster bomber and the project was canceled. But information was gathered about the structural and aerodynamic problems of very large aircraft, all of which would prove valuable some years later.
Boeing also bid for a second contract, intended to provide for the aerial defense of the United States against enemy fleets. This aircraft, the Boeing Model 299, became the B‐17 “Flying Fortress,” the most celebrated bomber ever flown by U.S. air forces. Developed and used operationally as a strategic bomber, especially in the World War II air assault on Germany, it became the embodiment of the beliefs Billy Mitchell had promoted so fiercely until his death in 1936. In its early days, the B‐17 was said to be able to fly fast and high enough to outrun most enemy fighters, and to be so heavily armed that it could defend itself even if intercepted, but these assumptions were rapidly proven false in the heat of combat. Out of over 12,000 B‐17s of all models built, nearly 5,000 were lost in combat, and almost 4,000 more in accidents.
In Europe, its principal theater of operation, the B‐17 was used by the U.S. 8th Air Force together with the Consolidated B‐24 “Liberator” for day bombing, while RAF bombers undertook the night operations of a “round‐the‐clock” combined bomber offensive. Although flown in large formations to increase the firepower brought to bear on attacking fighters, the U.S. bombers suffered intolerable losses until the arrival of long‐range escort fighters like the P‐51D “Mustang.” The B‐17s and B‐24s bombed in formation from above 20,000 feet, releasing together when the lead aircraft's bombs dropped. This precision bombing method was intended to ensure great accuracy and target saturation. (As opposed to the night area bombing of the RAF, in which specific aiming points were chosen for the bomber crews, but it was accepted that the targets were whole German cities.) Unfortunately, combat and the European weather combined to degrade results and some commanders later described their operations rather ruefully as “area bombing of precision targets.” By the end of World War II, the combined bomber offensive had effectively destroyed most German industrial cities, with particularly catastrophic effects in Hamburg and Dresden.
At the tactical level, in operations aimed at influencing the surface campaign directly, twin‐engine bombers like the North American B‐25 “Mitchell,” Martin B‐26 “Marauder,” Douglas A‐20 “Havoc” and A‐26 “Invader” were used at medium and low level during World War II against specific targets such as rail junctions, bridges, supply depots, and troops concentrations. A‐20s and B‐25s also operated to particular effect against Japanese shipping during the Pacific War, notably during the destruction of a Japanese invasion fleet in the Battle of the Bismarck Sea. By contrast, in April 1942, B‐25s were used in a unique operation that had a strategic purpose. Lt. Col. James (Jimmy) Doolittle's B‐25 squadron was launched from the deck of the aircraft carrier Hornet to strike a symbolic blow against Tokyo.
The technique of dive‐bombing, intended for use against targets where great accuracy was essential, was promoted in the 1920s by the U.S. Navy and Marine Corps, and brought to fruition in combat by the German Luftwaffe in the 1930s. The Junkers 87‐B Stuka was a vital part of the German Blitzkrieg that led to the fall of France in 1940. The devastating effects of determined dive‐bombing were most graphically demonstrated by the U.S. Navy's Douglas SBD‐1 “Dauntless” dive‐bombers at the Battle of Midway in 1942, when they sank four Japanese aircraft carriers to shift the balance of power in the Pacific permanently in favor of the United States.
In 1944, Boeing's B‐29 “Superfortress” flew its first combat operations. Its internal bombload was 20,000 pounds, over three times that of the B‐17, and its combat range of 3,000 miles plus more than doubled that of its predecessor. Equipped with a pressurized cabin, a B‐29 crew could operate in comfort up to 30,000 feet. In the closing months of the war, B‐29s were used in massive raids on Japan, dropping enormous quantities of incendiaries to burn Japanese cities. The most destructive raid of World War II took place on the night of 9 March 1945, when more than 300 B‐29s bombed and burned Tokyo. An estimated 84,000 people died and more than 1 million were made homeless. The firebombing of Japan continued until August, when two single B‐29s, named Enola Gay and Bockscar, ended World War II with the atomic bombings of Hiroshima and Nagasaki, respectively. The postwar period then saw the development of the policy of deterrence, in which the threatened use of nuclear weapons was intended to deter war, and the start of the unending public debate on the morality of using strategic airpower, either conventional or nuclear, to attack enemy populations.
After World War II, the jet engine revolutionized bomber aircraft. In the late 1940s, the USAF's first truly intercontinental bomber, the massive Boeing B‐36, improved performance by the addition of four jets to its six piston engines. The first U.S. bombers to usher in the pure jet age, however, were the North American B‐45 and the Boeing B‐47 in 1947. The B‐45 was built before swept‐wing theory was understood and was quickly overshadowed by the B‐47, which introduced thin, swept‐back wings, six axial‐flow jet engines mounted in pods, and “bicycle” main landing gear. In 1952, Boeing added the eight‐jet B‐52 “Stratofortress,” a huge bomber that has remained an impressive instrument of war since its introduction. Originally conceived for the delivery of free fall nuclear bombs, the B‐52 was for many years the backbone of the twenty‐four‐hour‐a‐day alert flown by the USAF's Strategic Air Command (SAC). Progressive modifications have added the capability to carry cruise missiles and conventional high‐explosive bombs in various combinations. The B‐52's 5,000‐mile combat radius can be extended as required by air‐to‐air refueling, and it has the capacity to lift a total weapon load of over 60,000 pounds, as much as the maximum weight of a loaded B‐17 in World War II. During both the Vietnam War and the Persian Gulf War, the B‐52's internal stowage of eighty‐four 500‐pound bombs made it a formidable offensive weapon.
In the late 1950s, the USAF acquired a supersonic strategic bomber in the Convair B‐58, a delta‐winged aircraft that could exceed Mach 2. Its impressive performance allowed it to set numerous international records, but its high cost of operations led to withdrawal in 1970.
Designated as fighters (F), many of the smaller USAF jets were fitted with bomb‐carrying pylons under the wings and the association of aircraft types with specific roles became less certain. These multirole aircraft included the North American F‐100 and the McDonnell‐Douglas F‐4 Phantom. The Republic F‐105 and the General Dynamics F‐111 were both conceived for low‐ and medium‐altitude penetration of defenses, and were designed with internal weapons bays. All four types saw action in Vietnam with a variety of conventional ordnance, and all were capable of nuclear weapon delivery. The F‐111 also later carried out a successful strike against Libya. In the 1970s, the USAF began taking delivery of the McDonnell‐Douglas F‐15 and the General Dynamics F‐16. Both aircraft are capable of multirole operations and demonstrated the effectiveness of the new generation of “smart” weapons (guided bombs, stand‐off missiles, etc.) in the Gulf War.
Naval aircraft have followed a similar path in their development since World War II. The Douglas A‐3D “Skywarrior” and the North American A‐5 “Vigilante” were both designed as carrier‐borne strategic bombers, and the Douglas A‐4, Grumman A‐6, Vought A‐7, and McDonnell‐Douglas F‐18 are all tactical aircraft with multirole capabilities. The McDonnell Douglas/British Aeropsace AV‐8B Harrier is a more specialized close support attack aircraft, uniquely capable of vertical takeoff and landing, which is flown by the U.S. Marine Corps and can be used to deliver a variety of bombs and missiles.
In the mid‐1980s, the USAF received the first of its Rockwell International B‐1Bs, a supersonic strategic aircraft with both conventional and nuclear capability in bombs and cruise missiles. Sophisticated electronics provide the defensive systems and the B‐1B can achieve near sonic speeds at low level. Even further advances have been made with the introduction of “stealth” technology, which reduces both the radar and infrared signatures of an aircraft dramatically. The Lockheed F‐117A demonstrated the effectiveness of its stealth design when it penetrated Iraqi airspace at will during the Gulf War, destroying critical command and control facilities with “smart” bombs. One F‐117A frequently accomplished what would have required several hundred B‐17s in World War II.
The next page of the “stealth” story was turned with the first flight of the Northrop B‐2 in 1989. The aircraft is a “flying wing” with no vertical surfaces, masked engine intakes and exhausts, and internal weapons stowage for nuclear weapons or up to eighty 500‐pound bombs. In a world dominated by multirole aircraft, the USAF's futuristic B‐2 is the closest approach to the classic “bomber” as Billy Mitchell would have understood the term—an aircraft of intercontinental range, which can leap over armies and navies, penetrate the defenses of an enemy nation, and strike devastating blows from the air.
[See also Airborne Warfare; Bombing, Ethics of; Bombing of Civilians; Korean War: U.S. Air Operations in the; Strategy: Air Warfare Strategy; Vietnam War: U.S. Air Operations in the; World War I: Air Operations in; World War II, U.S. Air Operations in.]
Edward Jablonski , Air War, 1979.
Enzo Angelucci , The Rand McNally Encyclopedia of Military Aircraft, 1983.
Bill Gunston , American Warplanes, 1986.
David Wragg , The Offensive Weapon, 1986.
Robin Cross , The Bombers, 1987.
Michael S. Sherry , The Rise of American Air Power, 1987.
Richard Hallion , Strike from the Sky, 1989.
Ron Dick , American Eagles: a History of the United States Air Force, 1997.
Daniel March & Chris Bishop, eds., The Aerospace Encyclopedia of Air Warfare, 1997.
AIRCRAFT, BOMBER. The first bomber developed by the United States, the Martin MB-1, first flown in August 1918, was developed too late for use in World War I. In the 1920s the United States had only a few British DH-4 and Martin NBS-1 bombers, which the celebrated general William (Billy) Mitchell used to sink retired battleships to prove his theory that a separate air force could successfully defend the U.S. coastline. The twin-engine, 107 mph Key stone biplane was standard until 1932. The Boeing Y1B-9 twin-engine all-metal 188 mph monoplane replaced the Key stone but was eclipsed by the Martin B-10, which, at 210 mph, was faster than any other American pursuit plane. Its replacements were the Douglas twin-engine 218 mph B-18 and the Boeing four-engine B-17.
World War II was fought with bombers developed during the late 1930s and early 1940s. They were designed for strategic bombardment or for tactical and supplemental strategic tasks. The main strategic bombers were the Boeing B-17 Flying Fortress and the Consolidated twin-tailed B-24 Liberator. Both were used in Europe, but the B-24's greater range made it more valuable in the Pacific arena. The B-17F and the B-17G, armed with twelve .50 caliber guns, carried 4,000 pounds of bombs over 2,000 miles at 300 mph; the B-24H and the B-24J, similarly armed, carried a 2,500-pound payload about 1,925 miles at 300 mph. The Boeing B-29 Super-fortress, the war's largest bomber, carried twelve .50 caliber guns. Both the B-29A and the B-29B carried 20,000 pounds of bombs and had a range of 5,000 miles.
Medium and attack bombers carried out tactical and supplemental strategic tasks. The medium bombers included the North American B-25 Mitchell, used in Lieutenant Colonel Jimmy Doolittle's famous Tokyo Raid in 1942, and the Martin B-26 Marauder. Both were heavily armed, twin-engine, midwing planes capable of 285 mph flight speeds, with a range of 1,100 miles. Quick and highly maneuverable, attack bombers operated at low altitudes. The Douglas A-26 Invader (1944) was the war's most advanced medium—a 360 mph twin-engine mid-wing carrying eighteen .50 caliber guns, 6,000 pounds of bombs, and fourteen rockets and ranging over 1,000 miles.
The first intercontinental bomber, the Consolidated-Vultee B-36 (1946), attained a maximum speed of 383 mph and carried 10,000 pounds of bombs 7,500 miles. Fully jet powered bombers were developed late because of the jet engine's high fuel consumption. The first was the North American B-45 Tornado (1948), powered by four jets, with a maximum speed of 579 mph, a 10,000-pound payload, and a 1,910-mile range. The second fully jet powered bomber, the Boeing B-47 Stratojet, came armed with twin radar-aimed .50 caliber tailguns. The B-47 replaced the B-29 and the B-50 as a medium bomber until it was retired during the 1960s.
In 1954 the Boeing B-52 Stratofortress began replacing the B-36 as the mainstay of the Strategic Air Command. Powered by eight jets, the B-52G attained a maximum speed of 650 mph and carried 65,000 pounds of bombs. Refitted for low-altitude flight, the B-52 served remarkably into the twenty-first century. General Dynamics's B-58 Hustler served the Strategic Air Command through 1970. Powered by four jets, its maximum speed was 1,324 mph with a 1,200-mile combat radius. It carried "mission pods" under the fuselage, or four nuclear weapons underwing, as it had no internal bomb bay.
The U.S. Air Force's mid-1970s bomber force included the B-52G, the B-52H, the B-56G, and a few General Dynamics FB-111A bombers. Derived from the F-111 fighter-bomber, the FB-111A carries 37,000 pounds externally and internally at subsonic speeds; once the ordnance is dropped, the maximum speed is Mach 2.2. The FB-111A remained operational until the development of the B-1 class of bomber in the 1980s. Intended as a successor to the B-52 Stratofortress, Rockwell International's B-1 was a variable-wing strategic bomber that could fly low to penetrate radar defenses. The prototype B-1A, which first flew in 1974, could reach twice the speed of sound at high altitudes while carrying nuclear bombs to their targets.
The development of stealth technology removed the only glaring weakness of the bomber as a tool of mass destruction: its vulnerability to radar detection. The B-1B, airborne by 1984, incorporated some stealth features, including contoured exteriors built of radar-absorbing materials. Despite the prohibitive cost, research and development into stealth planes—aircraft that would be invisible to enemy radar—culminated in the Northrop Grumman B-2 advanced technology bomber, first flown in 1989. Like the single-seat fighter Lockheed F-117A, which debuted in 1981, the B-2 uses a pyramid-shaped fuselage and swept wings made of carbon-fiber composites and high-strength plastics to reduce its radar signature. Engine intakes and exhausts are set low to the surface to avoid leaving a heat trace. Although the B-2 is slow, hard to maneuver, and can carry only limited munitions, it proved devastatingly effective during NATO's extended bombing campaign against the Serbian regime in Kosovo, Yugoslavia, in 1999 and in Operation Enduring Freedom in Afghanistan in 2001 and 2002.
Craven, Wesley F., and James L. Cate, eds. The Army Air Forces in World War II. Volume 6: Men and Planes. Washington, D.C.: Office of Air Force History, 1983.
Gunston, Bill. American Warplanes: A Full-Color Technical Directory of 200 of the Most Important Combat Aircraft to Serve the United States. New York: Crescent Books, 1986.
Wagner, Ray. American Combat Planes. Garden City, N.Y.: Doubleday, 1981.