Master military strategist Carl von Clausewitz argued that the key to war was to attack the center of gravity of the enemy's capacity to wage war. By World War I, the center of gravity was no longer the army but the factories and the workers who produced the engines of war. The distinction between soldier and civilian, critical to all modern notions of military morality, dissolved. The ability to wage war disappeared when the factories did. But given the location of factories, by necessity in cities, any attack on these factories would kill not only workers but also their children, and the milkman's children. This was, by definition, total war — the only war that could be waged in the industrial age.

At the outset of World War I, there was no way to destroy war-critical factories or populations from a distance. But as with most things, a problem found a solution close at hand. Aircraft made their appearance on the European battlefield during World War I — first as observation planes, then as fighters tasked with shooting down observation planes, and then as bombers tasked with destroying targets identified by reconnaissance aircraft.

Targeting the Industrial Plant

Geopolitically, it was clear that World War I had not solved the fundamental problem of Europe and that another war was inevitable. Among those who believed this were the theorists of air power. Chief among these was Giulio Douhet, an Italian who thought through the reality of war at the time and concluded that the chief solution would be the destruction of the enemy's war-making capacity. Douhet believed this would best be achieved by aircraft attacking cities en masse and destroying them. Joined in this view by the American Gen. Billy Mitchell and Britain's Hugh Trenchard, Douhet argued that the key to warfare was to use large numbers of massed bombers to annihilate cities. This would achieve two things: It would destroy the enemy's industrial plant and trigger a revolt by the public against the government. Because both sides would have massed bombers, the key to war was to launch attacks greater than the enemy's potential response by both having a larger air force and destroying the enemy's ability to produce more aircraft.

The inter-war air strategists were in part shaped by the carnage they saw in protracted trench warfare. Douhet believed that the role of air power was almost purely offensive, requiring rapid and destructive attacks against first the opposing forces' aircraft and then against civilian industrial and commercial centers. Trenchard, like Douhet, saw air power as a strategic and valuable force. Where Trenchard differed from his Italian contemporary was in considering ground forces still important and suggesting joint ground and air operations against enemy airfields. Early American air theorists, including Mitchell and the Army Air Corps Tactical School, viewed the role of strategic bombing as targeted against the war-making capacity of the enemy, rather than against the enemy morale, as Douhet and some European counterparts considered. Mitchell saw attacks on industry, communications and transportation as the real objectives of strategic air power and saw the armies in the field as false objectives.

Douhet implicitly recognized the weakness of aircraft, which was the same as the weakness of rifles: They were extremely imprecise. In 1940, when the British began launching attacks on Germany, the imprecision of the bomber was so great that German intelligence could not figure out what they were trying to bomb. Only massing bombers and destroying cities would work.

The Germans used this dual strategy in the Battle of Britain. They failed both because of lack of sufficient weapons and an air force not designed for strategic bombardment (which is what attacks on cities were called) but for tactical support for ground warfare. The British adopted nighttime area bombardment, making no secret that their goal was the destruction of cities to suppress production and generate political opposition.

The United States took a different approach: precision daylight bombardment. The Army Air Corps Tactical School sought to make bombing more efficient by finding and identifying bottlenecks in the opponent's supply chain. Targeting the bottleneck would reduce the total number of bombers, men and bombs needed to achieve the same ultimate goal as large city bombing. The Americans felt that they could solve the problem of inaccuracy and total attacks on cities through technology. They developed the Norden bombsight, which was supposed to enable the dropping of iron bombs with precision. The bombsights were delivered to the planes by armed guard, and the bombardier was ordered to destroy the bombsight at all costs if shot down. Regardless of this technology, U.S. bombing was not much more accurate than the deliberate randomness of the British.