Battle of the Ruhr The Battle of the Ruhr was a 5 - month long campaign of strategic bombing during the Second World War against the Nazi Germany Ruhr Area , which had coke plants , steelworks , and 10 synthetic oil plants . The campaign bombed twenty - six major Combined Bomber Offensive targets . The targets included the Krupp armament works ( Essen ) , the Nordstern synthetic - oil plant ( Gelsenkirchen ) , and the Rheinmetal - Borsig plant in Düsseldorf . The latter was safely evacuated during the Battle of the Ruhr . Although not strictly part of the Ruhr area , the battle of the Ruhr included other cities such as Cologne which were within the Rhine - Ruhr region and considered part of the same " industrial complex " . Some targets were not sites of heavy industrial production but part of the production and movement of materiel . Although the Ruhr had always been a target for the RAF from the start of the war , the organized defences and the large amount of industrial pollutants produced that gave a semi - permanent smog or industrial haze hampered accurate bombing . Before the Battle of the Ruhr ended , Operation Gomorrah began the " Battle of Hamburg " . Even after this switch of focus to Hamburg , there would be further raids on the Ruhr area by the RAF — in part to keep German defences dispersed , just as there had been raids on areas other than the Ruhr during the battle . Offence and defence . The British bomber force was made up in the main of the twin - engined Vickers Wellington medium bomber and the four - engined " heavies " , the Short Stirling , Handley Page Halifax and Avro Lancaster . The Wellington and Stirling were the two oldest designs and limited in the type or weight of bombs carried . The Stirling was also limited to a lower operational height . Bombers could carry a range of bombs - Medium Capacity bombs of about 50 % explosive by weight , High Capacity " Blockbusters " that were mostly explosive , and incendiary devices . The combined use of the latter two were most effective in setting fires in urban areas . British raids were by night - the losses in daylight raids having been too heavy to bear . By this point in the war , RAF Bomber Command were using navigation aids , the Pathfinder force and the bomber stream tactic together . Electronic navigation aids such as " Oboe " , which had been tested against Essen in January 1943 , meant the Pathfinders could mark the targets despite the industrial haze and cloud cover that obscured the area by night . Guidance markers put the main force over the target area , where they would then dropping their bombloads on target markers . The bomber stream concentrated the force of bombers into a small time window , such that it overwhelmed fighter defences in the air and firefighting attempts on the ground . For most of the Battle of the Ruhr the Oboe Mosquitoes came from one squadron No . 109 . The number of Oboe aircraft that could be used at any time was limited by the number of ground stations . The USAAF had two 4 - engined heavy bombers available : the B - 17 Flying Fortress and B - 24 Liberator - neither carried a bomb similar to the blockbuster bomb . USAAF raids were by daylight , the closely massed groups of bombers covering each other with defensive fire against fighters . Between them , the Allies could mount " round the clock " bombing . The USAAF forces in the UK were still increasing during 1943 and the majority of the bombing was by the RAF . The German defence was through anti - aircraft weapons and day and night fighters . The Kammhuber Line used radar to identify the bomber raids and then controllers directed night fighters onto the raiders . During the battle of the Ruhr , Bomber Command estimated about 70 % of their aircraft losses were due to fighters . By July 1943 , the German night fighter force totalled 550 . Through the summer of 1943 , the Germans increased the ground - based anti - aircraft defences in the Ruhr Area ; by July 1943 there were more than 1 , 000 large flak guns ( 88 mm calibre or greater ) and 1 , 500 lighter guns ( chiefly 20 mm and 37 mm calibre ) . This was about one - third of all anti - aircraft guns in Germany . Six - hundred thousand personnel were required to man the AA defences of Germany . The British crews called the area sarcastically " Happy Valley " or the " valley of no Return " . Bombing during the Battle . During the battle other German targets received large attacks . Outcome . In his study of the German war economy , Adam Tooze stated that during the Battle of the Ruhr , Bomber Command severely disrupted German production . Steel production fell by 200 , 000 tons . The armaments industry was facing a steel shortfall of 400 , 000 tons . After doubling production in 1942 , production of steel increased only by 20 percent in 1943 . Hitler and Speer were forced to cut planned increases in production . This disruption caused resulted in the " Zulieferungskrise " ( sub - components crisis ) . The increase of aircraft production for the " Luftwaffe " also came to an abrupt halt . Monthly production failed to increase between July 1943 and March 1944 . " Bomber Command had stopped Speer ' s armaments miracle in its tracks " . At Essen after more than 3 , 000 sorties and the loss of 138 aircraft , the " Krupps works . . . and the town . . . itself contained large areas of devastation " Krupps never restarted locomotive production after the second March raid . Operation Chastise caused some temporary effect on industrial production , through the disruption of the water supply and hydroelectric power . The Eder Valley dam " had nothing whatsoever " to do with supplying the Ruhr Area . A backup pumping system had already been put in place for the Ruhr , and Speer ' s Organisation Todt rapidly mobilized repairs , taking workers from the construction of the Atlantic Wall . The destruction of the Sorpe dam would have caused significantly more damage but since it was a stronger design less likely to be breached it was effectively a secondary target .