@KOOLHOVEN:
Actually,I think the He 117 had 2 engines per nacelle,giving it 4 engines.I love the old hunchback,but I vote for the Piaggio!
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Nope, only two engines.
In general, the Axis didn’t have as far to fly to get to the action and they didn’t ALWAYS need to cross some body of water (unlike Britain), so they didn’t need to develop 4 engine bombers until they were starting to lose the war, and by then they didn’t have the time or economy to work through the technology. The US and Britain were driven by the need for range and the ability to make it back to England or the Pacific Islands with functional engines - thus the redundancy of 4. Germany made much smaller hops, although once they had control of Western Europe they did desperately need more substantial bombers. They went with rockets instead.
As for Japan, it simply didn’t recognize the power of strategic bombing in a war of attrition; thus they were investing in naval strength and waiting for “the final decisive battle”. It wasn’t a priority of Japan to strategic bomb the allies as nearly as it was a priority of the US. Thus Japanese bombers were mainly all tactical - the Betty’s were torpedo bombers and medium payload at best and that was the primary bomber.
And Italy simply didn’t have the technology or military/political direction/ambition to build a heavy bomber.
I can only speak for myself, but I’d prefer the figures to denote the axis typical tried and true technology, not prototypes.