The US Strategic Bombing Survey Europe(USSBS) referred to by pbi and Shek was available (in part) in the old OPDP 7 study guide. It gives a good overview of the bombing campaign.
The Casablanca conference produced the following direction for the strategic bombing campaign "the progressive destruction and dislocation of the German military, industrial and economic system, and the undermining of the morale of the German people to a point where their capacity for armed resistance is fatally weakened." The RAF and USAF had somewhat divergent approaches on the bombing campaign as seen in the double-barrelled mission statement.
Area bombing (aimed at the morale of the German people) accounted for roughly a third of total tonnage dropped and perhaps half of the tonnage dropped on Germany. The RAF favoured area bombing while the USAF had faith in precision bombing. Precision bombing, however, requried complete air superiority to achieve. Specific target industries/facilities were sub pens, oil production and storage, aircraft and anti-friction bearings, transportation and "miscellaneous." The Germans adapted counter-mearures to the campaign (such as dispersion) and as noted in other posts made efficiencies under Speer. It does appear that the aircraft gasoline, railway system and Ruhr steel industries were hit hard. For example, by end 1944, railway carloading were reduced by 75 percent.
On the whole, the USSBS felt that "The most that can be saidis that bombing destroyed a substantial part of the consumer-goods cushion and thereby prevented further conversion to war production during 1944."
On the area bombing aspect, there were over 1,000,000 civilian casualties of whom just over 300,000 were killed. 20 percent of German dwellings were destroyed or seriously damaged. The USSBS felt that "bombing appreciably affected the German will to resist...War Weariness, willingness to surrender, loss of hope in German victory, distrust of leaders, feelings of disunity, and demoralizing fear were all more common among bombed than among unbombed people."
I feel that the bombing campaign did contribute to the defeat of Germany although it could not have done it on its own. Strategic bombing offered the only tangible means of bringing offensive action directly against Germany during the early and middle years of the war. It also had an effect on the ability of the Germans to respond to the Normandy invasion due to the shifting of strategic bombing empahsis towards transportation nodes.
Does this justify the civilian losses? I'm not sure and the answer one gives will probably depend on the point of view of the individual. It does appear that the war was won by the time of Dresden but it is much easier to look back than look forward in time. The bombing campaign should be judged in the context of the time. I would characterize Dresden as an example of "momentum." The bombing campaign had been ongoing for several years with high losses on both sides. I feel that the bomber offensive had achieved a momentum of its own at that point. I believe that the bombing of Dresden had little military value but was not a war crime.
2B