RAF daylight strategic bombing campaign results

drgondog said:

If you wish speed as the strategic alternative there is only one choice and that is the Mossie. IMO that selection points toward single or two ship formations to limit the intercept tracking and stretch German defenses. Single large formations, having no defensive firepower, seems foolish and in any case the loss rate will still be high. More effective? I don't see why the Mossie ability to deliver a bomb load better than a Halifax - on target - is improved unless the Mossie drops to the deck and makes its bomb run from there. In addition, Low altitude tactics influence fuel storage vs bomb load vs range calculations.

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Low altitude bombing does improve accuracy, but for the Mosquito it did have a couple of other benefits.

One, the German radar would not pick the intruders up as quickly, if at all.
Two, the Mosquito's performance at low level compared very well with the German fighters - Bf 109 and Fw 190.
Three, the Mosquito's great blind spot to the rear and below was not exposed.

The third is also applicable to the Lancaster and Halifax, as their defences did not cover beneath very well.
The downside was, of course, range is lessened.

Shortround6 said:

Even an Early Mustang with the Allison swapped for a Merlin XX may have trouble. Even with just four .50 cal guns it could go 7300lbs or more with full internal tanks. About 800lbs heavier than a MK V Spitfire. It may be faster but climb and turn won't be as good. ANd MK V Spitfires weren't good enough in 1941/42.

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You've still got basically the same set of trade-offs seen comparing the Mustang III/P-51B/C to the Spitfire IX. (range, level speed, dive acceleration, diving speed, energy retention at high speeds, roll rate)

Except compared to a Spit V, you'd have some modest advantages at low level with the MS gear of the Merlin XX. Possibly a slightly higher FTH due to ram performance too.

Edgar Brooks said:

Can we get one thing clear? The lack of supercharging had nothing, whatsoever, to do with bombing from 18,000', it was a deliberate policy of the Air Ministry.
Flying above 20,000' (and the Lancaster I could go to 23,000') brings the aircraft into the zone of contrails, and four white trails in the glare of moonlight, would have been (as the Air Ministry put it ) like fingers beckoning to every nightfighter within range, and a certain death sentence.
The two-stage Merlin was originally planned for bombers (in daylight,) but became unnecessary at night, hence the availability for the Spitfire.

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If there was a need to push altitudes a bit higher still while still working with Merlin XX level manufacturing/components capacity, wouldn't a 2-speed merlin with FS gear similar to the high-alt Merlin 47 be pretty feasible? (not 2-stage level performance, but enough to raise the ceiling a bit) Change in propellers for higher alt optimized performance might be useful as well.

pbehn said:

I think purely because of the distance it represents, the Rhur could be bombed fairly accurately by night using the gee system from beginning 1942. Hamburg was target more easily identified at night, the problem was with targets deep in Germany away from the coast. These targets however are as hard to find by day under normal European cloud as they are at night. By the time the US became successful at daytime raids they had a huge recon capability which wasnt there in 1941/2.

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I thought one of the points of this thread's premise was also considering the employment of precision bombing over area bombing. (one of the main reasons to even risk flying daylight missions) So ease of identifying area targets isn't as useful.

wuzak said:

One, the German radar would not pick the intruders up as quickly, if at all.
Two, the Mosquito's performance at low level compared very well with the German fighters - Bf 109 and Fw 190.
Three, the Mosquito's great blind spot to the rear and below was not exposed.

The third is also applicable to the Lancaster and Halifax, as their defences did not cover beneath very well.
The downside was, of course, range is lessened.

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Would the .303 guns on the British heavy bombers even be much use as defensive armaments from any position by 1942 or 43?

If .50 cal gun arrangements couldn't be adopted, optimization for unarmed, faster flying heavy bombers might be more practical as well. (and as with any unarmmed bombers, drop the tight formations in favor of dispersion as individual or very small formations)

kool kitty89 said:

If there was a need to push altitudes a bit higher still while still working with Merlin XX level manufacturing/components capacity, wouldn't a 2-speed merlin with FS gear similar to the high-alt Merlin 47 be pretty feasible? (not 2-stage level performance, but enough to raise the ceiling a bit) Change in propellers for higher alt optimized performance might be useful as well.

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I hope I don't appear rude, but you don't seem to be listening. Until Bomber Command returned to daylight raids, at the end of the war, the Air Ministry didn't want them to fly any higher than 18,000'. Here, there seems to be an obsession, at times, with aircraft/engine performance, while the authorities, here (contrary to the "Butcher" Harris title) did make efforts to keep their crews alive.

Would the .303 guns on the British heavy bombers even be much use as defensive armaments from any position by 1942 or 43?

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I recommend you read "Gunning For the Enemy," the story of tail/mid-upper gunner "Wally" Macintosh, who shot down 8 plus one probable.
Once "Village Inn" plus infra-red recognition and the gyro gunsight came into use, making tracer redundant (so the fighter pilot didn't know he was being fired at until too late,) things changed massively. This also increased the usefulness of the .5", hence the "Rose" turret.

If .50 cal gun arrangements couldn't be adopted, optimization for unarmed, faster flying heavy bombers might be more practical as well. (and as with any unarmmed bombers, drop the tight formations in favor of dispersion as individual or very small formations)

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Already being done with the Mosquito, which could plant a 4000lb "cookie" onto Berlin twice per night.

The original premise of this thread was:

"How would the RAF have faired if they had gone for a daylight strategic bombing campaign from 1941 on? Let's say the choice to go for a daylight campaign means they adopt the long range Spitfire variant for service as a escort. In 1941-42 the Luftwaffe was only fielding two Wings of fighters in the West, though I imagine the night fighters would have ended up as daylight bomber destroyers without a night campaign. Do the British go for high altitude bombing too?"

Now lets say, to follow up on this, that the Air Ministry has a change of heart/mind in late 1940/early 1941.and look at the technical aspects of trying to implement this tactic/policy. We may find that the air Ministry made the right decision.
1. It is too late to design a new fighter. Anything you start working on in Dec 1940/Jan 1941 won't show up in squadron service until the beginning of 1943 at best. That leaves you with modifying existing designs. Spitfire is the only with a hope of making 1941( and that would be summer or fall of 1941).
2. Without using a time machine to alter development schedule you have pretty much historic engines with historic deployment, no making hundreds of 2 stage Merlins in 1941.
3. With said time machine you have pretty much Historic bomber production. That is for numbers, maybe you can add a turret here and/or take a turret from there but no, you can't have 500 Lancasters in the spring of 1942. 7 Factories built Lancasters during the war but only 3 were doing it in 1942 and one of them (Armstrong Whitworth) only started in Sept of 1942 and built 30 aircraft by the end of the year. By the end of October 1942 they had built 493 Lancasters total.
4. People are confusing individual aircraft performance with formation performance. A Lancaster might very well have been able to fly at 23,000ft loaded with bombs, that doesn't mean A, that it could cruise at that height. B, that you could fly a large formation (even a squadron) at that height.
A. 23,000ft is the height at which it could still climb at 100ft per minute using 2850rpm and 9lbs boost. Max cruise (rich) was 2650rpm and 7lbs boost. Max lean was ????
B. In formation flying you have to plan speeds/altitude for the worst performing plane in the group/formation to be on the outside of a turn and a using it's max performance to stay in formation while the planes closer to the center of the turn use less power.

Not picking on the Lancaster, just using it as an example. NOBODY flew bombers (or fighters) in formation at their service ceilings. And if you don't fly the bombers in formation they are much harder to escort and much easier to shoot down.

More later.

Shortround6 said:

They could have. They did on some late war Lancasters or Lincolns.

However the two stage engines only show up in small numbers part way through 1942 and you need them for the fighters. There were four squadrons of Spitfires with two stage engines at the time of Dieppe in Aug of 1942. Packard built 5 two stage engines in 1942. They built 7250 single stage engines. Obviously RR was making them first but you won't have enough to do anything until the very end of 1942.

Dead on. In addition, it isn't clear that RAF BC achieve enough benefit of higher altitude performance at the expense of RAF FC

Forget Berlin. It is about 360-370miles from Norwich to Hamburg and about the same from Norwich to Frankfurt. A P-51 with 184 US gallons internal and 150 gals in drop tanks was rated at a 460 mile radius. With 269 US gallons internal and no drop tanks it was rated at 375 miles. Now can you get enough fuel into a MK V Spit (not a IX or VIII although you can use the same tanks) with it's Merlin 45 engine AND have enough performance to fight the interceptors?
That is what you have in 1941-42.

I would quibble on the Combat radius of a P-51B with internal 269 plus two 75 gallon drop tanks. The 355th performed a target escort of 1475 miles round trip to and from Stettin and Posnan on May 12, 1944. In fact all the P-51 escorts to Stettin, Berlin, Brux, Munich prior to ~ May 23, 1944 were performed with 75 gallon drop tanks. The typical cruise altitude to R/V was 22,000 feet - with a climb to escort altitude.

By inference the Spit would be escorting in mid altitude range which would be beneficial WRT fuel management in comparison with Mustang cruise altitudes. With the same fuel load internally (not possible w/o major redesign of the wing) the Spit could be cobbled to approach the same combat radius if 150 gallons could be carried externally. I suspect that the Spit spar(s) would have to be beefed up as well as G load design for landing at fully loaded gross weight.
Even an Early Mustang with the Allison swapped for a Merlin XX may have trouble. Even with just four .50 cal guns it could go 7300lbs or more with full internal tanks. About 800lbs heavier than a MK V Spitfire. It may be faster but climb and turn won't be as good. ANd MK V Spitfires weren't good enough in 1941/42.

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I agree that the Mark I/IA with Merlin XX would not have the same combat maneuverability as the Spit V but to me that suggests higher fighter vs fighter loss rate against the Fw 190/Bf 109 than achieved with the B but the I/IA w/Merlin XX loses in climb comparison but not much else. As an example it should turn better than the heavier P-51B even if climb 500 fpm less.

Having said that, the production tooling for mass manufacturing of any version of the P-51 wasn't acquired until mid 1943.

With a crystal ball and greater recognition of potential, a separate track for the XP-51 would have been to install a XX/1650-1 in parallel to the Allison. The bottleneck would still be the ability of Packard to generate enough engines to meet demands of RAF BC and P-51 production... suggesting that the Merlin engined MKI/IA still wouldn't be available in squadron level force until mid to late 1942.

Drgondog, no quibble from me on P-51 radius with max fuel. Just trying to show that with less than max fuel even the Mustang was only good for roughly 1/2 way into Germany.
So even if you could get 150 imp gal into a Spitfire AND hang 120imp gallons outside you get a radius of around 400-410miles (drag 10% worse than Mustang?). Now what hoops had to be jumped through to get 150gal imp into the Spitfire and what is it's performance like with a Merlin 45 or XX?
It just doesn't look like a viable project.
Jumping through larger hoops closer to the ground (300 mile radius) is easier and leaves the plane with more performance but a much more restricted target set. This makes defence for the Germans easier.

Going back to the bombers, the Lancaster was the highest flying bomber the British had (Mosquito excepted) with many of the others operating thousands of feet lower than the Lancaster. Stirlings, Manchester's and Whitleys all being rather low flyers unless operating at well below gross weight.
Whitley was always a night bomber, even before the war. Flying at 10-14,000ft in daylight against visually aimed AA guns wasn't a good idea even with fighter escort.
The bulk of the British bomber force in 1941/early 42 was Wellingtons with a lot of Pegasus engines.
Even if you had escorts the bulk of the British bombing force in 1941/42 wasn't really suited for daylight raids. Too low flying or too slow or both. Without totally revamping production lines (and starting that in 1940) the British are not going to get any sort of daylight bombing force (not counting token raids) until sometime in 1943.
Maybe those guys in the air ministry knew something after all

Shortround6 said:

Going back to the bombers, the Lancaster was the highest flying bomber the British had (Mosquito excepted) with many of the others operating thousands of feet lower than the Lancaster. Stirlings, Manchester's and Whitleys all being rather low flyers unless operating at well below gross weight.

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For what it's worth the Wellington VI had a ceiling of 36,700 feet at max weight -- 266 mph cruise at 35,000 feet.

While it wouldn't matter during 1941, if both the AAF 8th and BC were later daylight bombing the LW would have been much more effective in defense. Night fighters and day interceptors are have different requirements. The initial efforts to support both was a bit beyond the LW and industries capability and pushed Hitler to specify FLAK that, while inefficient, was more universal.

The American experience during 1943 was a tragic failure save for lessons learned. The RAF seemingly didn't have the mindset or equipment during 1941 for a better outcome.

Balljoint said:

The RAF seemingly didn't have the mindset or equipment during 1941 for a better outcome.

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Historically, in 1941, the RAF had already tried daylight bombing and found the cost unsustainable. It was developing the aircraft, tactics and technologies that would enable it, eventually, to launch a devastating night time campaign. It was not developing the aircraft, in the form of long range fighters, that would enable it to carry out another daylight campaign.
It proved late in the war that a blunt night time instrument could also be a very sharp daylight one, but only after the Luftwaffe was defeated.
Cheers
Steve

Shortround6 said:

1. It is too late to design a new fighter. Anything you start working on in Dec 1940/Jan 1941 won't show up in squadron service until the beginning of 1943 at best. That leaves you with modifying existing designs. Spitfire is the only with a hope of making 1941( and that would be summer or fall of 1941).
2. Without using a time machine to alter development schedule you have pretty much historic engines with historic deployment, no making hundreds of 2 stage Merlins in 1941.

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A greater emphais on higher altitude Merlin XX derivatives (or possibly even Hercules variants) should still have been practical in this timeframe. Again, not 2-stage performance, but enough to get operational combat ceilings a bit higher.

Puting an emphasis on turbochargers at that stage might have been useful, but unless the US's own policies for export (and turbo volume production) changed that'd mean setting up domestic British turbocharger manufacturing which probably wouldn't be available any sooner than the 2-stage merlin derivatives anyway. (perhaps more useful mated with Hercules engines, if a greater emphasis on supercharging alone didn't supplant the need there as well)

4. People are confusing individual aircraft performance with formation performance. A Lancaster might very well have been able to fly at 23,000ft loaded with bombs, that doesn't mean A, that it could cruise at that height. B, that you could fly a large formation (even a squadron) at that height.
A. 23,000ft is the height at which it could still climb at 100ft per minute using 2850rpm and 9lbs boost. Max cruise (rich) was 2650rpm and 7lbs boost. Max lean was ????
B. In formation flying you have to plan speeds/altitude for the worst performing plane in the group/formation to be on the outside of a turn and a using it's max performance to stay in formation while the planes closer to the center of the turn use less power.

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Yes, so any shift in doctrine to emphasize day bombing not only would need suitable escorts, but also developing/configuring bombers in a feasible manner. (in tersm of speed and especially altitude)

That would include managing practical loaded weights for the needed cruise altitude as well as using appropriate engines (and allotting said engines accordingly) ... and adapting aircraft to accept the most suitable engines as well.

And along with all that, followon plans for replacing obsolecent interim escorts and bombers with more capable ones.

Shortround6 said:

Drgondog, no quibble from me on P-51 radius with max fuel. Just trying to show that with less than max fuel even the Mustang was only good for roughly 1/2 way into Germany.
So even if you could get 150 imp gal into a Spitfire AND hang 120imp gallons outside you get a radius of around 400-410miles (drag 10% worse than Mustang?). Now what hoops had to be jumped through to get 150gal imp into the Spitfire and what is it's performance like with a Merlin 45 or XX?

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A side note on fuel carring capacity that I keep avoiding, but: would experimenting with wing-tip fuel tanks (fixed or expendable) have helped issues? They became common post-war and usually performed well aerodynamically, often reducing drag and even improving roll rate (at least when empty). Winglets might not have been understood during the period, but the so-called 'end plate effect' improving the effective aspect ratio of airfoils was at least known.

A clipped wing spitfire with fixed tip tanks seems light it might have been a useful development. (honestly this thought mainly occurred in the context of the P-39 some time back)

Shortround6 said:

The bulk of the British bomber force in 1941/early 42 was Wellingtons with a lot of Pegasus engines.
Even if you had escorts the bulk of the British bombing force in 1941/42 wasn't really suited for daylight raids. Too low flying or too slow or both. Without totally revamping production lines (and starting that in 1940) the British are not going to get any sort of daylight bombing force (not counting token raids) until sometime in 1943.
Maybe those guys in the air ministry knew something after all

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Would focus on re-engining (and shifted performance envelope targets for new marks entering production) make the Wellington situation any better?

Aside from that ... before the Mosquito hits volume production, a fast-bomber update to the Bleinheim might be useful in a similar role. A more direct Merlin (or possibly Hercules) powered conversion of the existing bomber than the heavier (and delayed) developments that the Beaufighter experienced. Admittedly a more limited bombload than the mosquito.


Fast bombers (be it early or late war) would be tougher to escort given the high cruise speeds and impact on range of escorting fighters ... but one of the major points of fast bombers is not using escorts as such at all. So focusing escort support on slow heavy/medium bombers in need of such (and possibly even allowing the fast-bombers to target beyond practical escort range) would make sense.

Any bombers simply too vulnerable to even practically escort (including sheer vulnerability to flak) would need to fall back to night raids. (but this could still have been a short-term tactic with emphasis on shifting strategies as soon as viable)

Greyman said:

For what it's worth the Wellington VI had a ceiling of 36,700 feet at max weight -- 266 mph cruise at 35,000 feet.

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With 2-stage merlins.

To manage anything approximating an earlier counterpart to that (but still lower altitude and unpressurized), you'd need some earlier higher altitude tuned engines. Single stage merlins (or maybe hercules) might have done the job well enough to get into the >20,000 ft cruise altitude range.

stona said:

Historically, in 1941, the RAF had already tried daylight bombing and found the cost unsustainable. It was developing the aircraft, tactics and technologies that would enable it, eventually, to launch a devastating night time campaign. It was not developing the aircraft, in the form of long range fighters, that would enable it to carry out another daylight campaign.
It proved late in the war that a blunt night time instrument could also be a very sharp daylight one, but only after the Luftwaffe was defeated.
Cheers
Steve

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Puting Emphasis on flak (and divided development resources) might still have occurred with bombing concentrated at lower 'high' altitudes and medium altitudes, let alone combinations of day and night bombing and fast+unarrmed/unescorted and slow+armmed+escorted arrangements.

Plus it doesn't just depend on what the RAF are actually planning/executing, but the predictions the Germans made regarding expected tactics. (granted, their own experiences with day and night bombing during the BoB probably would have been a reasonable yardstick there ... depending what LW and RLM officialls you actually look at)

Greyman said:

Fully loaded.

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Nope, according to Air Ministry data sheets it was 20k at max weight.

kool kitty89 said:

A greater emphais on higher altitude Merlin XX derivatives (or possibly even Hercules variants) should still have been practical in this timeframe. Again, not 2-stage performance, but enough to get operational combat ceilings a bit higher.

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Not really. There is a limit to what you can do with single stage supercharger and they were running into it. A Merlin 46/47 was rated at 1100hp at 22,000ft at 9lbs boost. So you picked up about 3500ft of altitude over a Merlin XX. Because of the single speed you lost about 100hp at take off. Granted with a two speed drive you can get some that back but you are still going to have less take of power than a Merlin XX or a mighty big dip in the power between low gear and high gear.

That would include managing practical loaded weights for the needed cruise altitude as well as using appropriate engines (and allotting said engines accordingly) ... and adapting aircraft to accept the most suitable engines as well.

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A climb chart from a B-17 shows the plane pretty much leveling out at bit above 36,000ft at a take off weight of 40,000lbs and needing over 240 gal and 130 miles to make the climb. At which point it pretty much has to turn around a land. At 50,000lbs it can make it to 35,000ft using about 440 gallons and 210 miles. 55,000lbs means About 33,000ft, 520 gallons of fuel and 250 miles. 65,000lbs means a bit over 28,000ft, 680 gallons burned and about 325 miles covered during the climb. A B-17 could pull 1000hp per engine for climb all the way to 27,000ft (it actually varied a bit from inner engines to outer because of different intake ducts). There is more than one reason for the US bombing from under 25,000ft.
Chart for a Lancaster at 65,000lbs show a climb rate of 300fpm at 19,000ft dropping to 100fpm at 22,000ft. plane would take 15 minutes to climb those 3,000ft. You can get a Lancaster to fly thousands of feet above 222-23,000ft, you just have to leave most of the bombs at home.
In 1941/42 the most suitable engine is the Melrin XX. At least if you want raids by more than a handful of bombers at a time.

Would focus on re-engining (and shifted performance envelope targets for new marks entering production) make the Wellington situation any better?

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Probably not. They were re-engining the Wellinton at this time. They were sticking Hercules engines in them instead of the Pegasus. It takes time to replace hundreds of bombers in the bomber force and the Pegasus powered planes were shuffled off to coastal command and training units although a number were brought back for the 1000plane raid on Cologne which rather tells you haw many better bombers were actually in service in the Spring of 1942.
Performance targets are going to depend on available engines, you can spec anything you want but if what you have (or can get) are 1600hp engines and not 1900hp engines where are you??

Aside from that ... before the Mosquito hits volume production, a fast-bomber update to the Bleinheim might be useful in a similar role. A more direct Merlin (or possibly Hercules) powered conversion of the existing bomber than the heavier (and delayed) developments that the Beaufighter experienced. Admittedly a more limited bombload than the mosquito.

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I kind of like the Blenheim but it was a rather limited airplane.
View attachment 287238
The big pipes under the outer wings are the fuel dump outlets. The long nose planes had long rang tanks in the outer wing the short nose planes did not have. In the event of an emergency early in the flight the plane could NOT safely land at the same weight it could take off at and the fuel in the outer tanks had to be dumped before landing.
Makes putting in bigger/ heavier engines a bit of a problem. The MK V Blenheim was beefed up for extra weights.
You also don't have an unlimited supply of engines. Perhaps a Merlin powered Blenheim might have been more useful but then what Merlin powered planes don't get built? They built 220 Twin Wasp powered Wellingtons in addition to the 400 Merlin powered ones due to shortages of Merlins and Hercules engines.

Fast bombers (be it early or late war) would be tougher to escort given the high cruise speeds and impact on range of escorting fighters ... but one of the major points of fast bombers is not using escorts as such at all. So focusing escort support on slow heavy/medium bombers in need of such (and possibly even allowing the fast-bombers to target beyond practical escort range) would make sense.

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The first part is a mistaken premise. The escorts cannot cruise at the speed of the bombers or slightly above or they will not be able to respond in a timely fashion to the attackers. The US escort fighters in 1943/44 routinely cruised at over 300mph weaving back and forth over the 180-200mph bombers. It can take a fighter doing 200-220mph over two minutes to accelerate to full speed. In two minutes a fighter doing 360mph can cover 12 miles. By the time a slow cruising fighter gets up to combat speed it is too late. For the second part, nobody has really figured out how fast is fast enough. A-20s that could do over 300mph were't fast enough, Mosquitoes were. where is the dividing line?

Any bombers simply too vulnerable to even practically escort (including sheer vulnerability to flak) would need to fall back to night raids. (but this could still have been a short-term tactic with emphasis on shifting strategies as soon as viable)

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Which is pretty much any and all bombers the RAF could field in practice in 1941/42 except for the Mosquito.

To manage anything approximating an earlier counterpart to that (but still lower altitude and unpressurized), you'd need some earlier higher altitude tuned engines. Single stage merlins (or maybe hercules) might have done the job well enough to get into the >20,000 ft cruise altitude range.

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Again, only if you leave most of the bombs home. At which point it starts to become why bother.

Denniss said:

Nope, according to Air Ministry data sheets it was 20k at max weight.

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The data sheets are for the Lancaster Mk.I/III drawn up in 1945. This is after the myriad of changes made to the type in the preceding three years (new engines, new engine limits, new equipment, new propellers, etc.)

The earlier Lancaster I (which I feel is more applicable to this thread and the one Edgar Brooks was probably referring to) used Merlin XX engines and at that time the maximum take-off weight was 60,000 pounds - compared to the data sheet Lancaster I/III at 68,000 pounds.

An A&AEE test of Lancaster I R5546 (4 x Merlin XX) at the maximum take-off weight of 60,000 pounds shows a service ceiling of 23,000 feet and an absolute ceiling of 24,500 feet.

In 1943 the maximum take-off weight was increased to 63,000 pounds. At Boscombe Down, Lancaster I W4963 (4 x Merlin XX) was tested and gave a service ceiling of 21,400 feet.

In 1945 they tested Lancaster I PD435 (4 x Merlin 24) at 72,000 pounds and had a service ceiling of 20,100 feet.

Shortround6 said:

Again, only if you leave most of the bombs home. At which point it starts to become why bother.

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I'm not necessarily disagreeing with any of your points but I just want to bring up the fact that - compared to the Lancaster, the Fortress did 'leave most of the bombs home', and the USAAF certainly still bothered.

I think some consideration should be given to how many bombers could be massed into a raid. Bomber command on night time raids wished the bomber stream to pass over flak belts and targets as quickly as possible to minimise losses. The same applied to night fighter opposition, even if a night fighter gets into the bomber stream there is a limit of time, fuel and ammunition to restrict losses. For d. Its OK to speculate about the Mosquito but that oisaylight escorted raids you need a large mass of bombers to destroy the target, to provide covering fire and to overwhelm flak and fighter opposition. The RAF was not in any position to mount raids of 500 single type raids with Halifax and or Lancaster until late in the war. Its Ok to speculate about what could have been done with hundreds (thousands) of mosquito bombers but in fact only a few hundred of each variant were built. The Mosquito performed well against defenses set up to repel massed day and night raids, if it was the only bomber then I am sure things would be very different.

The RAF were in a position to mount large daylight raids with the Lancaster and Halifax from 1943 onwards but chose not to, they concentrated on night raids as didn't have a suitable long range escort. In fact no one (incl USAAF) was able to operate effectively by daylight without suffering heavy unsustainable casualties unless they had escorts. Once escorts arrived then the USAAF became really effective and I do not doubt that the RAF could have made the switch with similar results but chose not to as they had become effective at night bombing and would have been second in the queue for escorts anyway.
Tempests were a very effective escort for RAF bombers and could escort raids to the Rhur which is an important target but other things called V1's caused a diversion of resources. To many demands and not enough Tempests was a problem.

Greyman said:

I'm not necessarily disagreeing with any of your points but I just want to bring up the fact that - compared to the Lancaster, the Fortress did 'leave most of the bombs home', and the USAAF certainly still bothered.

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A lot of this depends on the mission flown and mission planing. It is quite true that the Fortress did have a rather restricted bomb bay that limited the amount of bombs carried. The Lancaster could and did carry more bombs further than the Fortress but the difference may not be quite as much as is commonly supposed.
According to the end of the war data sheet for the Lancaster I/III (at 68,000lbs) it could carry 10,000lbs for 2250 miles using 2150 IMP gallons (2582 US gal) with 270 gallons being allotted for the "allowance" ( warm up, take-off, climb to height, reserve, etc) and 7,000lbs for 2680 miles using 2550 imp gal ( 3082 US gallons) with the same allowance. Ceiling at the 68,000lbs was supposed to be 20,000ft.
http://www.wwiiaircraftperformance.org/Lancaster/Lancaster_I_III_ADS.jpg

The manual (pilot's notes) for the B-17F G shows a range chart for a B-17 at 64,200lbs and carrying 6,000lbs as over 3000 (as much as 3200 miles) miles using 2812 US gallons at 25,000ft. Range changes with speed but the max range was at about 215mph true. Trouble with this is that it is a calculated range using NO ALLOWANCES. Actual range using similar allowance to the British might have been 10-20% shorter. Same manual but different chart shows the B-17 at 64,000lbs using 300 US gallons to climb to 20,000ft and using 110 miles. to get to 24,000ft from 20,000ft required another 120 gallons and another 60 miles.

Range chart : http://zenoswarbirdvideos.com/Images/B-17/17TRC.pdf

The different flight profiles and mission seriously affect practical range. British bombers may not have stooged around for anywhere near as long after take-off like the Americans did while getting all the planes into formation. They might not have spent as much time climbing to altitude before setting course for Europe (first way point). Americans may have very well been climbing to operational cruise heights after forming up but while crossing the Channel or North Sea. The outer wing tanks (Tokyo tanks?) may have been a fire/explosion hazard and not used unless really needed?

If Lancasters had tried flying the same type missions (or mission profile) as the B-17 they might not have carried the same bomb load either. Mission "profile" being take-off, then spend a 1/2 hour (or more) getting into formation and climbing to an intermediate altitude. Then set out for first way point on a course that includes several dog legs (nobody flew direct to target) and climbing to "operational" altitude by the time the formation crossed over land (or at least by first know flak concentration.)
Difference in "ceiling" between a B-17 at 55,000lbs and one at 64-65,000lbs was around 4,000ft. If you want the Lancaster to cruise at 23-24,000ft how may thousands of pounds of bombs/fuel are you going to have to leave behind?

The Lancaster will carry more bombs further than the B-17 but even with a 4-5000 difference in altitude the difference is not as much as it might seem.

I am sure that I have seen stats that showed on average the RAF Lancaster's and Halifax's averaged a 50% increased payload compared to the B17/24.

That may very well be but then they weren't flying quite the same mission. They weren't flying in formation which uses more fuel than flying independent even if in a bomber stream. They weren't spending several hundred gallons circling around waiting for the last planes of the formation to take-off. By flying several thousand feet below their "service" ceiling they saved another 100-200 gallons of fuel. Add it all up and there were several thousand pounds they could use for bombs that the Americans were using for fuel.
This is assuming the same target distance. If you want to use Lancasters and Halifax's on daylight raids using close formations for defense you have to take the bad with the good, and the bad means hundreds more gallons of fuel used per mission which cuts into the bomb load on all the medium and long range missions.