A Schnellbomber (German; literally "fast bomber") is a high-speed bomber. The concept developed in the 1930s when it was believed that a very fast bomber could simply outrun its enemies.
The first aircraft adopted for the Schnellbomber role was the Heinkel He 70, but it soon was replaced by the Dornier Do 17 in that role. In the 1937 air races in Switzerland the Do 17 won a number of speed records, apparently demonstrating the value of the concept. However, experience of the Spanish Civil War demonstrated that the Do 17's speed when loaded with military equipment was insufficient to escape interception, and armament had to be added to give it some defensive fighting capability.
While bomber development had temporarily outpaced fighter development in the 1930s, at the end of the decade fighters like the Hawker Hurricane and the Supermarine Spitfire entered service that had the performance to catch up with the Schnellbomber, and dramatically outgunning it by eight to one (only one gun would normally be able to fire back). The Do 17 suffered at the hands of the RAF, and production ended in 1940.
The Germans nevertheless persisted in their attempts to create newer Schnellbombers, as opposed to large bombers with heavy defensive armaments which was favored by the RAF and USAAF. Other aircraft recognized as Schnellbombers by the Luftwaffe were: the Junkers Ju 88, the first to be custom-designed for the role, three years before the start of the war, the Messerschmitt Me 410 Hornisse, and the jet-engined Arado Ar 234 Blitz (dubbed "the fastest bomber" – "Schnellstbomber"). Several other Luftwaffe aircraft were originally designed as fast bombers, but entered service in other roles; these include the Heinkel He 219 as a night fighter, and the Dornier Do 335 as a new Zerstörer heavy fighter. The Bomber B high-speed medium bomber design competition for the Luftwaffe started in July 1939 was meant to create an updated design to take over the original Schnellbomber role by later in World War II, and function with a heavier bombload than the earlier Schnellbomber designs were capable of carrying, but due to unavailability of the needed pair of high power output engines of 1,500 kW (2,000 hp) and above each - primarily the complex, 24-cylinder multibank Junkers Jumo 222 - needed for such designs, no production aircraft were ever ordered under the Bomber B program.
Ironically the most successful Schnellbomber of the war was the bomber version of the British de Havilland Mosquito. It retained a speed advantage over its enemies for much of the war, and was only able to be effectively countered by specialist versions of various night fighter designs. The Mosquito ended the war with the lowest loss rate among any aircraft in RAF Bomber Command. The Germans considered the Mosquito a superior implementation of their own Schnellbomber concept.