why so high?

[Baxter]

I have read a few books lately about air combat on different fronts and I am curious as to why the Allies bombed Germany from at least 20,000 feet. In Italy for example if you look at the operations that were flown by Wellington squadrons the normal bomb run for them was anywhere from 5,000 to 11,000 feet. I am wondering if 20,000 gave some sort of immunity from flak damage. Anyone know?

[flash]

Must be a number of reasons Gary - flak, getting fighters to them, bomb sights, fuel efficiency, weather. An 88 had an effective ceiling of 25,000 ft, the 105 and 128mm flaks could shoot higher but smaller stuff would be out of consideration.

[Tonx]

Thermal activity could be another consideration as to why the Allies chose height over German targets especially cities. In order to achieve accuracy the last thing that one needed was to be bumped around in thermal currents and thermally-generated turbulence. This would especially be the case once the raid had already started and fires were raging below - also at night when many of the raids took place the ambient temperature in general cools down compared with how it is during the day. Exacerbating such effects of thermal activity and particularly of concentrations like a burning city would produce. With a fixed bombsight the bomb-aimer needed stability in order to operate effectively and achieve what was deemed an accurate hit. Later on in WW2 when the Norden Bombsight was introduced bomb-aiming became less stability-dependent.

There also may have been some structural consideration given to the aircraft being exposed to moderate to potentially severe turbulence with such heavy bomb loads on board. Natural thermal activity can be encountered and cause CAT (clear air turbulence) at altitudes above 20,000 feet. These days thermal concentrations such as widespread bush and forest fires and volcanic activity (volcanic eruptions are of course handled differently) are not overflown directly because of their effects and the still greater heights that are affected by these.

It was only after WW2 that the truth behind bomb-aiming accuracy was revealed: With fixed bombsights some of the bombs dropped by RAF Bomber Command landed five miles away from their intended target even though they were dropped in relatively stable conditions.