Hi - my (limited) understand of the German Air Force during WW2 was that there was always a lack (and need) of a 4 engine heavy bomber. Why did the FW200 not fill the role?
Germany had several long-range heavy bomber programmes from the start of rearmament in the 1930s. The "Ural bomber" project recognised the possibility of war with the Soviet Union and thus requirement to bomb industry far to the east of Moscow and resulted in two four engine prototypes in 1936, the Dornier Do 19 and Junkers Ju 89, though lack of powerful engines meant the performance and payloads were disappointing. The death of Walther Wever, first Chief of Staff of the Luftwaffe and keenest proponent of strategic bombing, saw both designs cancelled and a greater emphasis placed on medium and dive bombers. Quantity was also a key consideration in the race for rearmament in the 1930 - Goering is quoted as saying "The Führer will never ask me how big our bombers are, only how many we have" - four engine aircraft were more expensive and complex to build.
The Ural bomber was succeeded by "Bomber A" in 1936, a requirement for an aircraft with a range of 5000km and speed of 550km/h resulting in the Heinkel He 177. The He 177 had four engines, but coupled them to drive two propellers. It had troubled development, though, the powerplants proving problematic, and the insistence of Ernst Udet that all bombers had to be capable of dive bombing required the airframe to be strengthened. Rather than the first units being delivered in 1939 as originally hoped the He 177 did not enter squadron service until 1942.
The Fw 200 was developed as an airliner, the first prototype flying in 1937; it could fly non-stop from Berlin to New York, but the Luftwaffe had no interest in it for a combat role (though it was used as a transport for Hitler and other VIPs). The Imperial Japanese Navy had, however, expressed an interest in a maritime patrol bomber variant and Kurt Tank was in the process of making such an adaptation when war was declared. The lack of a long-range bomber was not a major problem for the Luftwaffe during the campaigns in Poland and France where the tactical role was key, but it was a more serious issue for naval operations so the military variants of the Fw 200 ordered by Japan were taken into German service for long-range reconnaissance and orders for more were placed. They were successful in this role, and initially in anti-shipping attacks, but production was slow (less than 300 were built in total) and it had several failings as a combat aircraft due to its airliner origin, such as poor forward visibility for bombing attacks and an overloaded airframe. From Osprey's Fw 200 Condor vs Atlantic Convoy:
"The Condor’s ability to maneuver, absorb damage, and evade enemy interception was always problematic. The Fw 200 B was built to fly in thin air at medium altitudes, with no sharp maneuvering. Tank made the aircraft’s remarkable long range possible by designing a very lightweight airframe. Early military versions lacked armor plate, self-sealing fuel tanks or structural strengthening (...) Unlike purpose-built bombers that had some armor plate and redundant flight controls, the Condor was always exceedingly vulnerable to damage. (...) there were six large unarmored fuel tanks inside the cabin, which could turn the Condor into a blazing torch if hit by tracer ammunition. When Condors tried to maneuver sharply to avoid enemy flak or fighters, their weak structure could be damaged, leading to metal fatigue, cracks and loss of the aircraft."
In 1940 the Fw 200 did have one enormous advantage over the He 177 and the anti-aircraft defences of Allied merchant shipping: it existed. As the latter strengthened - more anti-aircraft guns fitted to merchant ships, more escorts, air cover initially from catapult launched Hurricanes (that had to find land or ditch at the end of their flight) then escort carriers - the Condors had to largely abandon bombing attacks, their most valuable role being supplying intelligence for U-boats. The Condor was never available in large enough numbers to seriously participate in the Battle of Britain or Blitz, and would have fared poorly against defended targets.
The He 177 finally reached squadron service in 1942 and was effective in the anti-shipping role using stand-off guided weapons but was never an entirely satisfactory aircraft. There were other projects, such as the "Amerikabomber" concept for an aircraft capable of attacking the USA from Germany, but none resulted in more than prototypes.