The German Luftwaffe, or Air Force, was officially formed in 1935 although in reality the Luftwaffe had been in semi- secret development long before then. (Prior to 1935, Germany had been banned from having an air force as a result of the Treaty of Versailles).
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The Luftwaffe was the most modern and best equipped air force in Europe with 1888 aircraft and over 20,000 officers and men.
At first, the Luftwaffe dominated the skies, but fought an increasingly futile war of attrition against superior Allied numbers, especially in the bloody Air Campaign over Europe and ultimately Germany.
World War II saw massive bombing of military targets and major cities. The big, slow-moving bombers operated in formations (sometimes numbering 1,000 or more) that were intended not to evade enemy defences but to beat them back or simply swamp them with numbers.
The key to bombing during the day was to provide an escort of fighters adequate to turn back defending fighters. (Anti aircraft artillery was of little hazard to bombers flying above 20,000 feet.)
During the Battle of Britain (1940-41), a typical formation of German He-111 and Do-217 bombers would cross the English Channel at about 15,000 feet. Close escort would be provided by Fw-190s weaving in and out of the formation, while high and top cover would be provided by Me-109s stacked behind the bombers up to about 25,000 feet.
The added height would enable the Me-109s to jump the RAF's Spitfires and Hurricanes while they were still climbing. Even more effective were fighter sweeps, in which Me-109s would leave the bombers and attack distant airfields before the defending fighters could get off the ground.
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But the Luftwaffe, in one of the major miscalculations of the aerial war, usually confined its fast, deadly fighters to a closer escort of the bomber formations. The U.S. Army Air Force learned the value of fighter sweeps in its long-range daylight bombing of Germany, but not before placing an unfounded faith in the capacity of its B-17 Flying Fortress and B-24 Liberator bombers to defend themselves with their own heavy armament.
Night bombing relieved bombers of the fighter threat (at least until effective radar was installed in planes), but it presented difficulties in finding and hitting targets. With visual navigation impossible except on the clearest moonlit nights, electronic aids became vital. In the blitz of London and other cities, the Luftwaffe used a system called Knickebein, in which bombers followed one radio beam broadcast from ground stations on the continent until that beam was intersected by another beam at a point over the target. Lead bombers dropped incendiary bombs, which set fires that guided other bombers carrying high explosives as well as more incendiaries.
source: Air Warfare: Britannica.com
source: The German Luftwaffe in WW II