…At the start of World War II, Britain and Nazi Germany were reluctant to launch major air raids against each other’s cities. But before long both countries authorized strategic air raids against each other’s urban areas. Gradually restrictions on the aerial bombardment of civilian populations were totally ignored by the combatants as each side vowed to retaliate for previous air strikes against its cities by the enemy.
U.S. and British bombing raids over Germany had different functions in the combined air war against Germany. The role of the British Royal Air Forces, which it adopted as its strategy, was predicated on “area bombing” - that is, large scale bombing of industrial and residential areas in order to break the morale of the German people by terrorizing them. The U.S. Army Air Forces once claimed that U.S. strategy was not based on destroying civilian populations even if it had that as the result.
“The leaders of the AAF had long been on record in opposition to indiscriminate attacks on civilians. If bombardiers were sometimes less circumspect in this manner, or if Germans found it hard to differentiate between spillage and terror bombing, it nevertheless seemed important during these pre-Hiroshima months not to deviate from the state policy of attacking legitimate military objectives.” (9)
The U.S. Army Air Forces explained the British preference for area bombing of Germany - “proposals to bomb Germany so terrifyingly that it would sue for peace” - on the grounds of the British revenge motive: “It is not surprising that proposals for all-out attacks on Berlin, the Ruhr or other critical areas of Germany always seemed to come from the British, who had undergone the German air raids of 1940-41 and were not  enduring the punishment of V-1’s and V-2’s [Germany rockets].” (10) At times the U.S. Army Air Forces even claimed to have opposed “proposals frankly aimed at breaking the morale of the Germany people” because of “the moral issue involved.” (11) Elsewhere, however, the Army Air Forces admitted that such statements “were meant strictly for home consumption.” (12)
The differences between the U.S. and British Air Forces were not based on morality. Initially the “general conclusion reached [by the U.S.] was that bombing of this sort [area bombing] while effective enough in producing general damage, was an unreliable and costly way of paralyzing the enemy’s war machine and that, in comparison, precision bombing of a specific phase of the enemy’s war economy according to a definite but flexible strategic plan afforded the most economical means of effecting a decisive concentration of bombardment.” (13)
The combined bomber offensive of the U.S. and Britain included continuous day and night bombing attacks against Germany. The U.S. daytime precision bombardment was designed to hit specific industrial targets which couldn’t be detected at night. The British flew night-time area bombing raids aimed at destroying entire urban areas associated with industrial or transportation targets.
Area bombing, and more specifically targeted attacks were calculated to complement each other. “By deploying both it would be possible to bring continuous 24-hour pressure to bear on the enemy, thus preventing his defenses from relaxing. It would also be possible, in many cases, for the AAF to locate difficult targets and mark them by fire resulting from the preliminary bombing, and so make it feasible for the RAF to complete the job at night.” (14)
The U.S. Army Air Forces had, in fact, “from the first been interested in the possibilities of incendiary attacks against the crowded and inflammable cities of Japan…” (15)
By early 1945 the U.S.-British arguments over terror bombing stopped - even when “strictly for home consumption.” First came the Allied fire bombing of Dresden. Then the U.S. shifted its strategy in Japan to include fire bombing on a vast scale.
Brigadier General Haywood Hansell, who had directed the strategic bombing attacks until mid-January 1945, did not agree with the fire bombing approach. He insisted that “precision bombing” be continued. On January 20, 1945, Hansell was replaced by LeMay. “Perhaps in the last analysis Hansell’s chief fault was in adhering too strictly to the ‘book’ - to doctrines of precision bombardment which he helped formulate-in the face of growing interest in area incendiary bombing evinced by [General Henry] Arnold [Chief of the Army Air Forces].” (16)
The idea was to prove that incendiary bombing and destruction on a vast scale could be the decisive aspect in the final results of the Pacific War.
U.S. air war strategists believed that fire bombing might be particularly effective against Japan because “[t]housands of small households or ‘shadow’ industries were jammed into the metropolitan sectors. Thirty percent of the nation’s total labor force worked in factories employing 30 persons or less. Most of these home factories were engaged in war production, were so widely scattered and lightly built as to be unsatisfactory pinpoint bombing targets-and were highly vulnerable to attack by fire. Precision bombing could still serve a limited purpose against isolated key war plants and against major fire-resistant plants in the urban areas; but for real results, intensive use of incendiary bombs would be the answer.” (17)
The U.S. bombing strategy of 1942-44 against Japan was expanded in a big way in March 1945, beginning with the fire bombing of Tokyo on March 9 and 10, 1945. The area of Tokyo selected was four miles by three miles, a zone with a civilian population density of 103,000 per square mile. A high concentration of incendiary bombs dropped from the huge U.S. B-29 Superfortresses ignited a series of fires, fanned by brisk winds, which raged out of control within half an hour, the result of which was that more than 15 square miles of Tokyo was burned out. About 100,000 men, women and children were killed and another 100,000 people were made homeless. According to the U.S. Army Air Forces: “No other air attack of the war, either in Japan or Europe, was so destructive of life and property.” (18) (19)
“With casualties of this order,” Clark wrote of the March 9-10 fire bombing of Tokyo, “it seemed inevitable that Japan could be burned into capitulation. The bomber, surely, might here do what it had failed to do against Germany: Eliminate the need for ground invasion.” (20)
Within 48 hours of the U.S. fire bombing of Tokyo, LeMay’s B-29 bombers launched incendiary attacks against Kobe, Nagoya, and Osaka. Over a 10 day period, 9,373 tons of bombs were dropped and 31 square miles of these cities were burned out. More fire bomb raids were carried out on Tokyo, and by the end of May 1945, 56 square miles of Tokyo had been reduced to ashes… (21)