In 1939, the scale of the BC raids was fall smaller, but percentage wise far worse for losses in some raids, like 10 of 22 Wellingtons being shot down to Wilhelmshaven. 8thAF never got hammered so badly on coastal targets like that.
Overall, Bomber Command had an attrition rate around 20% (31 lost of 173 planes)
Now a few years later, 376 B-17s bombed Schweinfurt for the loss of 60. 8thAF had around 17% average attrition rate in all of 1943, in far deeper raids and did far more destruction to both ground targets, and to the Luftwaffe.
The issue is not that the British targets were coastal, of course. It was that both over the coastal targets in 1939, and over the in-depth targets in 1943, the bombers were there unescorted. The USAAF was not slaughtered over coastal targets because coastal targets were within fighter escort range. The US bombers were slaughtered when they were unescorted in daylight - that's the similarity with the British raids of 1939.
Yes, the USAAF caused more damage to their targets than Bomber Command. That is a function of the total payload, more than anything else. Secondly, it's a function of the target size (the British were trying to hit thin ships, the US crews were happy if they dropped a bomb within the fences of large industrial plants). And it is not exactly a meaningful thing; if the US bombers could,
theoretically, cause more damage than the British ones had done in 1939, but the fact is that after a few attempts they are,
practically, not sent out to cause that damage, what good is the theoretical possibility?
Note that if we want to throw in the effects of the bombings, then we should not forget what were the objectives of the Ploesti and Schweinfurt raids. The US planners were operating under the wrong assumption that they could destroy "bottleneck" parts of the German war industries, thus achieving a KO outcome with just a few and targeted raids. It was ball bearings at Schweinfurt and oil at Ploesti. Under the respect of achieving the stated objective, the missions were total failures. They achieved widespread damage that the germans had to repair, caused temporary reductions in the outputs, and forced the Germans to redeploy further defenses, and to decentralize production; all useful results - in a holistic conception of the air offensive as a whole. But a complete shutdown, which is what was planned, was not achieved.
As to the losses and percentages, yes, the first raid on Schweinfurt and Regensburg, the one with 376 bombers, lost 60 bombers downed there and then. But the losses were higher if you consider scrapped bombers that made it home and were deemed too damaged to be repaired, and those heavily damaged ones that were simply abandoned in Algeria.
Tidal Wave had a loss rate of 30%, but that was an exceptional and admittedly very risky mission.
Then you have the second raid on Schweinfurt, were the losses amounted to 26% counting, again, the scrapped bombers.
While on the worst British mission of 1939 the loss rate was even higher (45%), functionally the outcome was
identical. In fact, the British stopped sending out such missions (and geared up for night bombing); the USAAF
also stopped sending out such missions. One could claim the USAAF was not slaughtered exactly as heavily as Bomber Command, from the POV of sheer mathematics; but it was just as heavily, identically slaughtered if we look at the reaction to the slaughter, withdrawing from those battles. That is because,
in both cases, the casualties were unsustainable.
