The British bombers did not have any superchargers as did the American planes. Thus they flew in amongst defending German fighters. Heavy losses caused a change in strategy and the Brits became night bombers. The Americans were able to fly higher and in the day time tending to use radar because of the cloudy nature of the continent. Neither practice was very effective in destroying individual small targets such as factories. City busting (fire bombing) was pretty much developed by the British because the cities were easy to find at night. Typically, the bombing was done in waves, one wave mostly incendiaries, another mostly block busters. Dresden was a combination British/American effort. The fires were set at night by two large waves of British planes (by this time there was little or no air defense). The Americans came the next day and bombed the rubble. Don't know about Hamburg.