intercepted, the bombers had enough firepower to drive off their attackers, and enough armor and resilience to absorb any damage their attackers might attempt to inflict. The Air Corps Tactical School developed a doctrine that became known as industrial web theory, which called for precision attacks against carefully selected critical industrial targets. Walker drove home his belief in bombardment with a famous dictum from his lectures: "A well-organized, well-planned, and well-flown air force attack will constitute an offensive that can not be stopped." Walker published another professional article in 1933, entitled "Bombardment Aviation: Bulwark of National Defense". "Whenever we speak in terms of 'air force' we are thinking of bombardment aviation," he wrote, dismissing other forms of aviation. This was orthodox at the Air Corps Tactical School, which taught that "every dollar which goes into the building of auxiliary aviation and special types, which types are not essential for the efficient functioning of the striking force can only occur at the expense of that air force's offensive power." Walker's major thesis was that "a determined air attack, once launched, is most difficult, if not impossible to stop when directed against land objectives." At the conclusion of his article, he renewed his call for the creation of an independent air force "as a force with a distinct mission, of importance co-equal to that of the Army and the Navy." Walker's persistent advocacy of strategic bombing led to frequent clashes with Captain Claire Chennault, who led instruction in pursuit aviation at the Air Corps Tactical School from 1931 to 1936. Chennault believed that the right mix of fighters and ground defenses could successfully defeat a bomber assault and ridiculed Walker for suggesting that bombers could not be stopped, leading to "legendary" debates between the two. In November 1934, Walker, now a student at the Command and General Staff School at Fort Leavenworth, testified with Robert Olds, Claire Chennault, Donald Wilson, Harold George and Robert Webster on the military aspects of aviation before the Howell Commission on Federal Aviation. All were current or former instructors at the Air Corps Tactical School, and all except Chennault were part of the Bomber Mafia. They argued for an independent air force, in contradiction to Army doctrine. Walker told the commission: "unless we create an adequate and separate Air Force, this next war 'will begin in the air and end in the mud'-in the mud and debris