Messerschmitt Me.210, part one

The Messerschmitt Me.210 was a German heavy fighter and ground-attack aircraft of the World War 2 which was designed to replace the Messerschmitt Bf.110. Its design started just before the outbreak of the conflict and its first examples were ready in mid 1939 but they left much to desire regarding flying characteristics, as the first prototype, named V-1, suffered serious wing planform and various fuselage flaws.
The design underwent a large-scale operational program through 1941 and early 1942 to fix it, but the flaws persisted.
It entered limited service in 1943 but it was almost inmediately replaced by the Me.410 which was a further development of the Me.210 but redesigned to shake off Me.210's reputation. The failure of the Messerschmitt Me.210 programme meant that the Luftwaffe had to keep relying on the outdated Messerschmitt Bf.110.
An order of 1000 exemplars was placed before the prototype was flown, and this proved to be an error because the first prototype of the Me.210, powered by two Daimler-Benz DB601B engines, flew in September 1939 and was considered unsafe by its test pilots. Stability was bad in turns, and it tended to oscilate even when flying level. At first, designers concentrated on the twin-rudder configuration that had been taken from the Bf.110 and replaced it with a single and much larger single vertical stabilizer. That change barely made any difference and the aircraft still tended to 'snake' while suffering also from terrible stalls. With the nose up or in a turn, the stalls led into a spin when the automatic leading-edge slats opened. In fact, the second prototype, named V-2, was lost that way in September 1940, when the pilot couldn't recover from the spin and had to bail out. The pilot commented that the Me.210 had "all the least desirable attributes an aeroplane could possess". In fact, it took up to 16 prototypes and 94 preproduction examples to try to resolve the many flying problems. However, as the RLM was desperate for a replacement for the Bf.110, they ordered full production for the type in early 1941.

Sources:
1. https://en.wikipedia.org/wiki/Messerschmitt_Me_210
2. https://forum.valka.cz/topic/view/1019/
3. Salamander Books - The Complete Book of Fighters