General bombing offensives basically mean city busting?
Which is defined whether the aiming is at specific targets, or a zone where the targets are known to be?
Operational factors would be navigational and bombardment accuracy, enemy defenses, and bomber escorts; Selective would be a desire to destroy specific industry and targets where the other is to bomb 'em and burn 'em 'till they quit.
And that didn't work because of a lack of effective deep-penetration escort, stiffening enemy air-defenses, and accuracy that was sub-par...
This was from September 1939 to some point in 1940? If I recall, they chose a selective bombing campaign because of the size of the bombing force, the PM's personal opinions, and FDR's requests to avoid attacks on civilians.
No. A selective campaign targets what we would now call target systems, oil, ball bearings, transport etc. The USAAF with rare exceptions always adopted this policy. A general bombing offensive might target far more nebulous objectives like enemy morale. In the case of the British effort it was an offensive to reduce German war production by any means possible. It degenerated into city busting, Harris is on the record stating that he was more interested in the acreage destroyed than factories flattened.
The method employed for a selective campaign might be precision or area bombing. The operational factors you identify determine which is achievable and whether there really is a choice. If you cannot reliably find or hit a relatively small target accurately (precision bombing)then you drop a lot of bombs in the area of that target in the expectation of hitting it (area bombing). The British (and I'm sure the American) did a lot of statistical analysis to work out how many sorties and what weight of bombs were required to guarantee the destruction of various targets.
The British chose a selective bombing campaign, as drawn up in the Western Air Plans because they thought it was the best application of the available air power. The re-think came when they realised that most crews couldn't find their targets, let alone hit them. The idea of a more general campaign was not new. For example, in WW1 the British attempted to bomb German or German occupied railway stations, but were not to bothered if the bombs missed the target and caused panic and damage elsewhere in the city/town. It was not considered a waste of effort.
You have to understand the bomber fleets of the major pre-WW2 powers as a deterrent. Everybody started with the intention of attacking purely military targets, not targeting civilians, in fact making a conscious effort to avoid civilian casualties. It wasn't long before this moral position started to slip on all sides and the RAF in particular had always had a strong influence from the Douhet/Mitchell/Trenchard line of doctrine. The RAF could not decide bombing policy in isolation, Britain is and was a democracy, not a military dictatorship. The gloves could only come off once sanctioned by the British government. By late 1940, much earlier than most appreciate, Bomber Command was pursuing its selective campaign by area bombing methods. On 30th October 1940, before Coventry was attacked, Sholto Douglas was writing to Peirse regarding attacking German towns and concluding
"The objectives considered most suitable for these concentrated attacks [on towns]
are the sources of power, such as electricity generating stations and gas plants, and centres of communications; but where primary targets such as the oil and aircraft industry objectives are suitably placed in the centres of the towns or populated districts, they also might be selected."
One glove was already off.
Coventry was bombed on 14th November 1940 and Mannheim was the British city chosen for reprisal for this attack, and also for the heavy raids on Southampton. The raid took place on the night of 16/17 December under the code name Operation Abigail Rachel. Bomber Command was given a special authorisation by the War Cabinet to carry out a 'general attack on the centre of a German city', and it was Bomber Command that chose Mannheim. 134 aircraft were sent to Mannheim (reduced fron the intended 200 )and did bomb the city, most bombs falling in residential areas, killing 34 people and injuring another 81. The special authorisation was precisely because, at this time, the British were still prosecuting a selective campaign.
British bombing policy evolved through 1941, there is a series of reports and mamoranda published in Volume IV of the official history, but any in depth discussion of these is beyond the bounds of a forum reply. On 18th August 1941 the infamous Butt Report was published, which showed just how inaccurate and ineffective Bomber Command's efforts had been.
Starting in May, it seem Churchill was more willing to adopt attacks on population centers but wanted to make sure the public was behind it before he'd do it. By July plans for incendiary raids were drawn up, but it wasn't until the Coventry raids that political unacceptable became political inevitable.
Actually by February 1941, there was a memorandum circulated that specifically stated that attacks on cities were aimed at demoralization by causing mass destruction and fear of death to the population down below..
The debate about morale attacks did not really gather pace until May/June 1941 when Trenchard himself produced a memorandum advocating German morale as Bomber Command's primary target. On 2nd 1941 June Sir John Gill, Chief of the Imperial Staff, commented on the memorandum.
"1. Lord Trenchard makes two points
(a)That our primary bombing target should be German morale
(b) That the building up of a strong bomber force should be given the highest priority.
The primary bombing target
2. There is, I think, general agreement that the Battle of the Atlantic must remain our chief preoccupation: after that our effort should be employed against the most profitable targets in Germany. The possibilities are:
(a) Morale
(b)Oil
(c) Transportation
The arguments in favour of attack on morale are set out in Lord Trenchard's paper" [Beyond the scope of a reply here].
Note that morale is top of the table. The debate continued for months, and it wasn't until
14th February 1942 (not 1941) that AVM Bottomley (Deputy Chief of the Air Staff) wrote to AM Baldwin (Acting AOC-in-C Bomber Command, pending Harris' arrival) instructing him that
"...it has been decided that the primary objective of your operations should now be focussed on the morale of the enemy civil population and in particular of the industrial workers."
Just one sentence in a directive of several hundred words, but now the gloves were really off. It had taken two and a half years of war before it happened.
Cheers
Steve