I would have to say January 1943 when the Allies actually got bombing around the clock organized. Soon after in August came Ploesti and so forth. The combined offensive was a force to be recconed with thus when the communication. On the other hand, the only way that there could be strategic bombing on Japan was when we got to Iwo Jima and Okinawa so as soon as we could bomb Japan it was pretty darn effective!

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Hence the saying: One may know how to conquer without being able to do it- Sun Tzu