Thanks to those supplying the oil type definitions.
Before the 15th Air Force finally received permission to officially target the Ploesti refineries it had been attacking the rail marshalling yards which were located roughly in the middle of the refineries, as part of the authorised transport targets. The bombing of these yards had been strangely inaccurate, more of the bombs appear to have hit the refineries than the rail lines. HE bombs unless noted
5 April 1944, 516.4 tons (including 140.9 tons of incendiaries) on the yards, 71 tons on Astra Romano refinery
15 April, 290.1 tons on the yards, 56.5 tons of incendiaries on the Industrial Area.
24 April 793 tons on the yards
5 May, 814.3 tons on the yards, 295.8 on oil pumping stations, 227 tons on refineries.
18 May, 493 tons on the refineries
General Spaatz deliberately waited until the weather was near perfect to order the first major oil attacks, the 8th Air Force did attacks on 5 synthetic oil refineries on 12 May with 1,383.6 tons of bombs out of 1,717.9 tons dropped that day, all visual bombing. October 1943 to May 1944, 8th Air Force tons of bombs dropped visually on Germany and their percentage of total bombs dropped on Germany for the month, 3,015.2 - 72.05%, 1,483.8 - 27.56%, 2,705 - 30.41, 2,053.4 - 24.78%, 7,073.8 - 54.14%, 4,920.3 - 33.61%, 11,813.8 - 77.34%, 11,487.9 - 57.79%. Bombs dropped on Germany final quarter of 1943, 18,462.1 tons, dropped in May 1944 19,800 tons. To put it another way of the total wartime bomb tonnage dropped by the 8th Air Force on Germany 5.22% by end 1943, 18.9% by end May 1944.
USSBS, The How and Why Air attacks crippled the German Oil-Chemical Industry
""Production loss at Ammoniakwerk Merseburg, at Leuna, on the other hand, was due entirely to reparable damage. Following the first two attacks, 94 percent of the utilities damaged had to be repaired before the plant could start up again. Compressors and pumps could run with tarpaulins strung overhead, but pipe and cable breaks had to be patched up. By November, there had been over 1,500 breaks in the Leuna water piping system alone, and in all 22 attacks on the plant over 5,000 individual breaks were sustained by the utilities distributing systems."
"The Leuna versus Allied air forces bout resembled in some ways a prize fight. The plant was knocked down nine times but never out, and recovered rapidly at first but more slowly as the accumulating punishment began to tell. Its recovery capacity also slackened as indicated by the decreasing percentages of the recovery plans. It might be said that the plant was finally defeated on points. To have achieved a complete knockout the Allied air forces would have had to destroy its recovery capacity, and they did not deliver a sufficiently strong punch to accomplish this."
After the 22 raids the USSBS thought it could recover to around 70% capacity in a couple of months.
The US first tried H2S in September 1943, by end February 1944 two 8th Air Force bomber groups had been equipped with H2X, end May it was 6, end July 11, end August 24. Then add the acute shortage of people trained to use the sets and the way February serviceability of the sets was around 77% while for the second half of 1944 it was around 88 to 90%. The 8th pioneered using radar and had teething problems like crews switching between radar and visual and back again in the middle of a bomb run, which made things worse. In mid 1944 the radar and Norden sight were used together to eliminate this. The idea should have been to bomb blind and take a visual shot as a "bonus" not decide the other way round at the last moment.
As bombing usually suppressed economic output instead of destroying it the bombers needed to mount a sustained attack, otherwise as per Arthur Harris objections, the Germans would be back to about normal output sometime after the weather turned bad. The USAAF needed radar bombing to mount a sustained offensive and the way European weather works the 8th Air Force needed every group to have bad weather bombing abilities, the 15th could usually expect good weather each day over some useful target between France and Bulgaria, enabling a more measured introduction of H2X. The output of radar sets and people trained to use them remained a problem to around the end of 1944.
The book America's pursuit of Precision Bombing by McFarland confirms the 8th had the worst blind bombing accuracy, the 15th and 20th Air Forces and Bomber Command were more accurate. The 15th was about twice as accurate as the 8th in combat conditions. In 285 test runs the 8th found 55.5% of bombs within 4,000 feet, 68.1% within 5,000 feet for an average crew, exceptional crews had 50% of bombs within 2,500 feet. Combat errors were considered to be 1.5 to 2 times the test runs. The 20th could land 50% of bombs in combat conditions within 5,500 feet. The British, in combat conditions (presumably at night) had 50% within about 6,400 feet (1.2 miles).
It appears a lack of instructors, the need to train so many people, the way tour expired men were temporarily held back to be trainers instead of being sent home to the US all meant the 8ths training program was the worst and the results followed. The 8th had a 4 week course. The British a 6 month course. The 15th had a 5 day initial course followed by 40 hours in the air, 20 bomb runs, with a 3,000 foot error from 15,000 feet as the pass. Graduates then became 3rd or deputy lead for at least 10 real missions.
In order to build enough fighters and have the trained aircrew the Luftwaffe cut bomber production in 1944, add things like the night fighter force had 342 Ju88 on 31 January 1944 and 647 on 10 September. The Luftwaffe cut its bomber units due to them being ineffective in the west, and replaced by V-1, and not as effective as the ground attack units in the east, as well as fuel reasons. The Luftwaffe training system decreased due to lack of safe training areas and the time it would have taken to produce new aircrew as well as the fuel situation.
Losing Ploesti was a problem for the Heer in the east as it was drawing supply directly from it, with the refineries knocked out the option remained of shipping the crude oil to refineries elsewhere, hence the campaign of mining the Danube. The fighting in Normandy and in general did not put a big strain on Heer fuel supplies until operations became mobile. Using reserves and the importance of the fighting meant the mid 1944 German operations only suffered shortages due to tactical fuel supply, not strategic, that came later.
The following is a rather artificial calculation of Bomber Command's damage potential. Start with the average number of aircraft of each type and crews available for the month, multiplied by the average war time bomb load for the type, then multiplied by accuracy, that is the percentage of bombs that landed within 3 miles of the target located German cities (excluding Berlin) for the month in good to fair weather at night (in other words where the bombing photographs could identify location). The first column is all aircraft, the second is the Mosquito bomber contribution only, giving an idea of how many more Mosquitoes were required to match the overall damage potential.
aircraft with crew times bomb load times accuracy equals damage potential
Feb-42 11.73 0
Apr-42 14.95 0
Jun-42 26.05 0.2
Aug-42 24.36 0.19
Oct-42 29.98 0.29
Dec-42 30.16 0.28
Feb-43 42.72 0.76
Apr-43 58.02 0.84
Jun-43 131.03 1.29
Aug-43 155.07 2.11
Oct-43 158.26 2.37
Dec-43 175.52 2.75
Feb-44 181.76 2.3
Apr-44 249.89 4.76
Jun-44 288.92 6.49
Aug-44 328.97 8.18
Oct-44 459.69 10.43
Dec-44 515.47 13.88
Feb-45 476.39 15.21
Apr-45 567.83 19.48
Lots of approximations with this calculation but it essentially says at night over Germany, assuming the aircraft could carry their average bomb load to target then for the month the average amount of potential damage done to the target by the average number of aircraft and crews available nightly is the given number. In June 1943 the average bomb raid would cause about half the damage of June 1944, bomb raids in the second half of 1943 would cause a third to a half the damage of raids run in the second half of 1944, thanks to a combination of greater accuracy, more aircraft and the increasing percentage of Lancasters in the main force bomber units during 1944, from an average of 475.6 with crews in January to 932.5 in December. The better performing Halifax III started to be issued to Bomber Command in September/October 1943, in February 1944 it was over half the force, heading to around 90% in May. Average bomb loads for the war, Stirling 6,622, Halifax 7,539, Lancaster 10,065, Mosquito 2,383 pounds.
Bomber Command was being defeated over Germany in early 1944, the USAAF was rebounding from its October 1943 defeat and fighting hard, according to the USAAF Statistical Digest losing to enemy aircraft, 139 heavy bombers in January, 170 in February, 178 in March, 314 in April and 211 in May, total 1,012, losses for the rest of the year were 504. The 8th started 1944 with 25 operational heavy bomber groups, to 29 end February, 35 mid May, finally 40 on D-Day, on the face of it a 60% increase in strength, in fact what was called effective strength for combat (operational aircraft with an operational crew) went from an average of 723 heavy bombers in December 1943, to the following for the first 6 months of 1944, 822, 981, 960, 1,049, 1,304, 1,855, or about a 260% increase in strength. For the 10 months July 1944 to April 1945, the combat strength figure averaged 1,840.
On 15 January 1944 the 15th Air Force reported an effective strength of 155 B-17 and 71 B-24, total 226, up to 305 on 18 January, on 10 May 1944 when its final heavy bomber group did its first operation 200 B-17 and 623 B-24, total 823, 9 May strength was 891, 11 May strength was 934. Daily figures tend to fluctuate.
A successful campaign against German liquid fuel production could only start a matter of days to weeks, not months before it actually did in 1944, until then the allies lacked everything, acceptable loss rates, numbers, accuracy, bad weather capability. The earlier the campaign starts the more time the Germans have for building passive and active defences, start early enough and there is the option for Germany boosting synthetic oil production capacity.
The bombing campaign was very end weighted, not only in terms of bombs dropped but also the effectiveness of the bombs (better explosives and more explosive content, better size and type mixtures) and their accuracy along with the amount dropped in a given time - the ability to sustain daily operations, thereby giving the quantity of damage done a quality of its own through cumulative effects and overwhelming the repair system.
The attack on oil deprived the Germans of their tactical mobility, the attack on transport their strategic and economic mobility, adding up to more than the sum or the parts, as has been noted interdicting coal shipments to the synthetic oil plants played a part in reducing output.