The U.S. Army requirement for bombers during the Great War was delayed by disagreements over the numbers and types to be purchased. With no confidence in U.S. capability, the Army leadership decided to buy English Handley-Page and Italian Caproni aircraft designs for construction in the United States. These U.S.-built aircraft were modified for the Liberty 12 engine.
The development of U.S. bombers can be traced back to the Martin GMB (MB-1) -- the first significant order for a U.S.-designed type. The GMB's primary role was as a reconnaissance scout plane with bombing only a secondary role. The GMB's first flight was just before the end of WWI and marked the end of bomber development for more than a year in a period of rapid disarmament and very limited funding for aircraft design and procurement.
In September 1919 the Air Service adopted a new naming scheme with 15 types based on aircraft design mission. Three bomber types were created: Type XI for Day Bombardment (DB), Type XII for Night Bombardment - Short Distance (NBS) and Type XIII for Night Bombardment - Long Distance (NBL). The most significant bomber of this period was the NBS-1 (MB-2), which was basically an enlarged and strengthened GMB.
In 1923 the Army adopted yet another naming scheme for some of its bombers. The Type XI aircraft category was replaced by the Light Bombardment (LB) type. The Heavy Bombardment (HB) type was used briefly in 1926-1927. The final naming scheme of using just the letter B to designate a bomber was begun in 1926 with the Huff-Daland (Keystone) XB-1 and incorporated some of the former LB bombers renamed using the new system.
Throughout the 1920s, bombardment aircraft performance lagged that of pursuit aircraft. The rather large, wood and metal bi–plane bombers were under-powered for the bomb payloads they carried. In the mid–1920s the Materiel Division of the Army Air Corps urged industry to begin the development of 4 engine mono–plane bombers. However, the War Department overruled the Materiel Division’s efforts.
After the Great War, some military theorists believed that in the next war the airplane could prevent the kind of static, immobile trench warfare that had been recently experienced, thereby making war once again an effective instrument of national power. The US Army Air Service "Bombardment" text of 1924-1925, which argued that bomber aircraft were nothing more than large caliber guns that could out-range and out-strike other types of guns, and thus harass infantry columns and interfere with the concentration of troops. The most original and influential of these theorists was the Italian General Giulio Douhet, who argued that in the future, bombers would spare the lives of soldiers by moving the battlefield from the trenches to the cities. American theorists embraced the application of bombers against enemy cities, but made the distinction between combatant and noncombatants.
The most influential of the American theorists was Brigadier General William “Billy” Mitchell. In July 1921, Army bombers in a special demonstration for the Navy, sank several former German warships, including the battleship Ostfriesland, by air bombing. At that time there was a great deal of discussion about the role of the airplane as a weapon. Air Service leadership saw in these trials a glimpse of a seemingly invincible anti-shipping weapon that would give flyers the advantage in the battle for coastal-defense dollars.
Mitchell argued that “the most effective use of bombardment aviation is the attack of sea craft.” Mitchell was antagonistic toward the Navy. He argued continually that no warship could survive a determined air attack, yet thousands of aircraft could be purchased for the cost of one battleship. Both the new Air Corps and the Navy saw themselves as the first line of American defense, and both sides considered themselves as true strategic weapons.
It was recognized that an airplane which could carry a large bomb load a considerable distance from its base, and be able to defend itself from enemy fighters, would be desirable. However, neither aircraft design nor materials had advanced enough to make such a thing possible.
Bombers for Coastal Defense
Among other objectives, Mitchell's air power crusade sought to obtain for the Army air arm the mission of coastal defense. At stake was not only the prestige which went with being the first line of continental defense against an invader, but the opportunity to develop and procure the long range bomber.
The Army-Navy competition focused on which service had responsibility forcoastal defense of the hemisphere. While both services competed for funds to producedesired quantities of aircraft, Congress became increasingly concerned with duplication ofefforts. Several joint aviation boards were formed to attempt to appease Congress by defining separate service responsibilities for coastal defense. The service chiefs finally reached an agreement (the MacArthur–Pratt agreement of 09 January 1931) where the Army was given primary responsibility for coastal air defense.
Because of the strong isolationist attitude in the United States at the time, the opportunity for the Army air arm to obtain the funds needed for development of the bomber were slim, but the coastal defense mission with its prerogative of ranging far out to sea from land bases to bomb enemy ships approaching our coasts was adequate justification for long-range bombers. In the course of his campaign to obtain the coastal defense mission, Mitchell's impatience and zeal resulted in his 1926 court martial and resignation from the service.
The thrust of this airpower thinking can be illustrated with a lecture given by 1st Lt Ken Walker, an instructor from 1930 to 1933. Walker began by stating that bombardment was “the backbone of any air force.” As such, it must be the dominant arm of the Air Corps, with pursuit and observation units acting in support. Walker argued that, given the defensive posture of the United States, the first and most obvious target for the bombers would be an enemy fleet approaching the coast. Such a fleet would never be able to land an invading army as long as the Air Corps could control the air over the ocean approaches to US shores—naval vessels were helpless in the face of air attack.
Walker assumed the United States would be on the strategic defensive, and suggested that enemy air bases near the United States — in Central or South America — would present the greatest threat. The mission of bombers would be to destroy those air bases.
In August 1931 they were given another chance to prove their prowess. The Navy had an obsolete cargo ship, the USS Mount Shasta, which needed to be sunk—the Air Corps could do the honors. Not only could the airmen barely locate the ship 60 miles out to sea, but their bombing accuracy was abysmal. One bomb hit the ship but did little damage. Much to the airmen’s humiliation, the Mount Shasta was then sunk by surface ship gunfire. Once again airmen blamed poor weather, inadequate bombsights, and bombs too small for the job at hand. The papers had a field day, and various headlines exclaimed, “The Bomb Flop” and “Naval Supremacy Found Upheld by Air Bomb’s Failure”.
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