Once they started bombing the oil production systems and ball bearing factories I´d consider pretty effective. otherwise you just watch the production figures rise until autumn 1944 under Speer and realize that at least the results were not what you´d expect them to be.
Hmmm, can't agree I'm afraid. The 'Battle of the Ruhr' early 1943 was the point when strategic bombing went from a nuisance to a crisis.
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!
Actually, the strategic bombing of Japan began after the conquest of the Mariana Islands in mid-1944. It was from airfields on Tinian, Guam, and Saipan that the great streams of B-29 intercontinental bombers flew. Iwo Jima was seen as an emergency airstrip for damaged aircraft on their return flights from Japan. JT