At first the RAF was forbidden to bomb targets in Germany for fear of civilian casualties, and concentrated on dropping propaganda leaflets at night. German air defences savaged daylight operations focusing on bombing strategic targets. By spring 1940 it was clear this strategy had failed. Bomber Command began to fly at night, but suffered navigation and target identification problems, along with a rapidly improving German defence.
Aircraft were deployed to support operations against tactical targets in Norway during the German invasion. The German invasion of France and the Low Countries followed, but there was now a thought-out plan for Bomber Command to follow - partly based on the bombing of strategic targets in Germany. A division of Bomber Command, together with the Advanced Air Striking Force (based in France), attacked communication targets, while the remaining squadrons attacked oil installations and refineries in the industrialised Ruhr area.
After France fell, Britain's small strategic bombing force was mainly occupied in anti-invasion operations; the Blenheims bombed barge concentrations in the Channel ports, and the night bombers (the Wellingtons, Hamptons and Whitleys) attacked oil installations and aircraft factories in Germany. Strategic bombing and Bomber Command were now Britain's only means of taking the offensive directly to Germany. As a result, Bomber Command began to hold a key place in British strategy.
During 1941 the first of the four-engined heavy bombers were used and the number of operational squadrons increased. Although Bomber Command was required to attack naval targets in France and Germany (on Churchill's orders), German ports remained more popular targets than those on the French Biscay Coast, as they were closer to the original RAF concept of strategic bombing.
The 'Transportation Plan' in 1941 concentrated on bombing German rail links. In August the Butt Report raised serious questions about photographs taken at the point bombers dropped their bombs. It appeared few of the bombers (who claimed to have successfully hit their targets) were getting near the correct aiming point, and errors were being measured in miles, not yards. But scientific aids to navigation and bomb aiming were being developed and soon vastly increased effectiveness.
Heavy losses persuaded Bomber Command to limit its activities at the end of 1941. However, with the appointment of Air Chief Marshal Harris in 1942, Bomber Command once again undertook heavy and decisive bombing attacks. Although individual operations (such as the attack on <<Lübeck>> or the 1000 bomber raids on Cologne and Bremen) were considered as tactically very successful, they could not be translated into complete strategic successes in the face of the sophisticated German air defence network. The Americans could not achieve a decisive defeat thorough strategic bombing either, and operations decreased.