a few large air battles fought in daylight later in the month and into October, the Luftwaffe switched its main effort to night attacks. This became official policy on 7 October. The air campaign soon got underway against London and other British cities. However, the Luftwaffe faced limitations. Its aircraft—Dornier Do 17, Junkers Ju 88, and Heinkel He 111s—were capable of carrying out strategic missions but were incapable of doing greater damage because of their small bomb-loads. The Luftwaffe's decision in the interwar period to concentrate on medium bombers can be attributed to several reasons: Hitler did not intend or foresee a war with Britain in 1939, the OKL believed a medium bomber could carry out strategic missions just as well as a heavy bomber force, and Germany did not possess the resources or technical ability to produce four-engined bombers before the war. Although it had equipment capable of doing serious damage, the Luftwaffe had an unclear strategy and poor intelligence. The OKL had not been informed that Britain was to be considered a potential opponent until early 1938. It had no time to gather reliable intelligence on Britain's industries. Moreover, the OKL could not settle on an appropriate strategy. German planners had to decide whether the Luftwaffe should deliver the weight of its attacks against a specific segment of British industry such as aircraft factories, or against a system of interrelated industries such as Britain's import and distribution network, or even in a blow aimed at breaking the morale of the British population. The Luftwaffe's strategy became increasingly aimless over the winter of 1940–1941. Disputes among staff revolved more around tactics than strategy. This method condemned the offensive over Britain to failure before it began. In an operational capacity, limitations in weapons technology and quick British reactions were making it more difficult to achieve strategic effect. Attacking ports, shipping and imports as well as disrupting rail traffic in the surrounding areas, especially the distribution of coal, an important fuel in all industrial economies of the Second World War, would net a positive result. However, the use of delayed-action bombs, while initially very effective, gradually had less impact, partly because they failed to detonate. The British had anticipated the change in strategy and dispersed its production facilities, making them less vulnerable to a concentrated attack. Regional commissioners were given plenipotentiary powers to restore communications and organise the distribution of supplies