1944: Flak Alone Blasts the Allies out of the Sky

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Lars
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Post by Lars » 18 Jan 2005 09:57

Tony Williams wrote: If you're relying on contact fuzes for direct hits the shells don't need to be as big. So fire sub-calibre shells at a high velocity to improve their altitude performance! TW
As for target destruction, the Luftwaffe set some rules of thumb, saying that three or four hits from a 20mm cannon would destroy a single-engined fighter, 20 hits a heavy bomber. (I assume this refers to the performance of the MG 151/20.) Apparently the 30mm MK 108 was sufficiently powerful that a single hit was claimed to be able to destroy a single-engine fighter or medium bomber, and four hits a heavy bomber. It was assessed that 360 grammes of HE was required to destroy a heavy bomber.

Basically this means that a hit from a 50 mm shell (weight 2.2 kilo) anywhere on a four engine bomber should destroy the plane. The 88 mm shell was in fact overkill (weight 9.4 kilo), that much explosives wasn´t really needed if the aim was a direct hit (as opposed to the indirect hits from fragments of the time-fused shells) .

However, the problem was that the 50 mm gun had a maximum effective ceiling of 5.6 km. It would take an improvement of the gun (not the shell) to change that. Make the barrell of the 50 mm gun longer and add more explosives for the shooting and we probably have a fast firing 50 mm flak gun aiming for direct hits that would reach up to 8-10 kilometers. Again, the conclusion is the same: RAF and USAAF heavies are cooked, and again this was possible with a rather low-tech solution. No ME 262, no HE 219, no Wasserfall, no air-to-air rockets, just an improved 50 mm gun!

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Post by Tony Williams » 18 Jan 2005 13:03

A 50mm gun would not have been capable of achieving such a performance - the calibre of the barrel limits the amount of power you can push down it (think of it as the cylinder of a piston engine).

However, a gun of 88mm calibre can fire sub-calibre saboted 50mm projectiles at very high velocity, which could achieve the desired performance.

TW

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Post by Lars » 18 Jan 2005 13:47

Tony Williams wrote:A 50mm gun would not have been capable of achieving such a performance - the calibre of the barrel limits the amount of power you can push down it (think of it as the cylinder of a piston engine).

However, a gun of 88mm calibre can fire sub-calibre saboted 50mm projectiles at very high velocity, which could achieve the desired performance.

TW
Would saboted 50mm projectiles have a higher velocity than the 88 mm projectiles from the 88mm/flak 41(1 km/sec)?

And how would the the rate of fire from 50 mm sabot fire from 88mm gun compare to the normal 88 mm shot?

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Post by Lkefct » 18 Jan 2005 19:43

Sabot rounds are not going to have the long range that a big heavy shell is going to have. It is a momentum deal, and the sbot rounds, while the maintain a very high kinetic energy, have a lot less momentum. A better compomise might be a 75 mm shell, at a somewhat higher velocity then the 88mm shell. It is actually very difficult to hit a moving target so far from a gun. I don't think firing a single shot is going to be that effective, mostly because even smaller automatic cannons use air burst shells (any footage vs Kamakazies demonstrates that). Flak rounds all have a impact fuse as well, in case you happen to hit a plane, it just isn't likely. Bigger shells might be the answer, not the other way around.

in truth, I don't think the effective altitude is all that important in this case. The idea of the max effective altitide is that you want several shots as a plane as it passes a single battery of guns. The German flak is often taking on a stream of hundreds of bombers. They didn't try to track all the planes. They fired shots up into an immaginary box, and let the planes fly through it. They don't need to track, just keep firing. It removes a lot of the estimates that go into effective shooting.

One of the lessons the armericans found was that the higher they flew the less accurate their bombing. So, b29's might well want to fly very high, but that might also mean they have to come back again, in order to drop enough bombs on the target. Unless there is a way to accurately estimate the winds effecting the bomb on the way down, and the precise speed and direction of the planes relative to the target, any bombing from high altitudes is largely a good deal of luck, even today. This is why the USAAF used to all drop their bombs at the same time, to drop their bombs in a pattern, rather then individually. It is also why eventually the US went to mostly smart bombing.

The b-29's actual flight performance was a huge advantage over the other american bombers. The cruising speed of a b29 is higher then a b24 or b17. Since it takes a fighter a long time to climb to 30,000 ft, it makes it hard to mass a lare # of fighters against them, particuarly if the fighters take so long to get to altitude and then have to catch the bombers. Japanese fighters had particuarly slow climb rates to the higher altitudes compared to the FW 190, and Bf109, and are also not as strong performers at higher altitudes compared to the german aircraft. I don't think the added performance is that helpful vs Germany. It is a major factor vs Japan. The primary advantage is of course the added range. While it is possible to use a b29 in europe, a b17 and to a certain degree the b24 just don't have the range necessary to operate in the pacific. Also, the added complexity is probably more of a vulnerablity to the large heavy flak guns, rather then the b17 and b24, who are unpressurized, and have fewer hydaulics.

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Post by Tony Williams » 18 Jan 2005 22:43

Lkefct wrote:Sabot rounds are not going to have the long range that a big heavy shell is going to have. It is a momentum deal, and the sbot rounds, while the maintain a very high kinetic energy, have a lot less momentum. A better compomise might be a 75 mm shell, at a somewhat higher velocity then the 88mm shell. It is actually very difficult to hit a moving target so far from a gun. I don't think firing a single shot is going to be that effective, mostly because even smaller automatic cannons use air burst shells (any footage vs Kamakazies demonstrates that). Flak rounds all have a impact fuse as well, in case you happen to hit a plane, it just isn't likely. Bigger shells might be the answer, not the other way around.
Depends on the type of saboted shell. Germany built and fielded during WW2 a railway gun, the 28 cm K5 E, which fired full-calibre shells out to a maximum range of 62 km - most impressive. They also produced a smooth-bored version of the same gun - the K5 Glatt - for firing fin-stabilised saboted sub-calibre shells (the Peenemunde Pfielgeschosse), and that reached out to no less than 151 km. A modern 120mm tank gun firing APFSDS will theoretically reach out to 135 km if the barrel could be elevated enough. Germany was actually working on various saboted and squeeze-bore AA shells at the end of the war precisely in order to improve the altitude and time-of-flight performance.

The problem with time fuzed shells is that the fuzes were not precise, so it was quite likely that a shell which would have scored a direct hit would be detonated too early, doing no damage. Also, the fragments from an AA shell often damaged planes but much less often brought them down. So it was calculated that a contact fuze gave a better chance of success. Especially since you didn't have to spend time setting each fuze - you just chucked the round in the breech and the gun could be fired at its maximum rate.

There can be no doubt that before the advent of proximity-fuzed shells (which changed everything), the optimum solution for attacking large, high-flying bomber formations with AAA was to use sub-calibre, contact-fuzed shells.

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Post by Lars » 19 Jan 2005 10:19

Tony Williams wrote:
The problem with time fuzed shells is that the fuzes were not precise, so it was quite likely that a shell which would have scored a direct hit would be detonated too early, doing no damage. Also, the fragments from an AA shell often damaged planes but much less often brought them down. So it was calculated that a contact fuze gave a better chance of success. Especially since you didn't have to spend time setting each fuze - you just chucked the round in the breech and the gun could be fired at its maximum rate.

There can be no doubt that before the advent of proximity-fuzed shells (which changed everything), the optimum solution for attacking large, high-flying bomber formations with AAA was to use sub-calibre, contact-fuzed shells.
I´m not that convinced. By some estimates 3,343 shells costing a total of 267,440 reichsmarks ($107,000) were required to bring down one bomber. That´s an awfull lot of money to bring down one bomber. As it were, the Germans had major supply problems because of the ammo expenditure of the Flak arm. Ammunition consumption soared from a monthly average of 500,000 shells in 1941/42 to 3,175,400 shells in December 1944! At peak strength over 2 million soliders and civilians are involved in ground anti-aircraft defenses. 30% of all gun and 20% of heavy ammuninition production went for air-defense in 1944.

Tony´s and von Shadewald´s solution (no time fuses) mens that the rate of fire goes up. BUT if it also means that the ammo expenditure goes through the roof (ratio of shells/each plane destroyed goes up), the Germans would actually be worse off as they simply couldn´t produce more shells.

You may have a point Tony and Shadewald, but you need to make it likely that the costs of bringing down a bomber would go down.

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Post by Lars » 19 Jan 2005 12:21

Lkefct wrote: One of the lessons the armericans found was that the higher they flew the less accurate their bombing. So, b29's might well want to fly very high, but that might also mean they have to come back again, in order to drop enough bombs on the target. Unless there is a way to accurately estimate the winds effecting the bomb on the way down, and the precise speed and direction of the planes relative to the target, any bombing from high altitudes is largely a good deal of luck, even today.

The b-29's actual flight performance was a huge advantage over the other american bombers. The cruising speed of a b29 is higher then a b24 or b17. Since it takes a fighter a long time to climb to 30,000 ft, it makes it hard to mass a lare # of fighters against them, particuarly if the fighters take so long to get to altitude and then have to catch the bombers. Japanese fighters had particuarly slow climb rates to the higher altitudes compared to the FW 190, and Bf109, and are also not as strong performers at higher altitudes compared to the german aircraft. I don't think the added performance is that helpful vs Germany. It is a major factor vs Japan. The primary advantage is of course the added range. While it is possible to use a b29 in europe, a b17 and to a certain degree the b24 just don't have the range necessary to operate in the pacific. Also, the added complexity is probably more of a vulnerablity to the large heavy flak guns, rather then the b17 and b24, who are unpressurized, and have fewer hydaulics.
I agree that speed was probably the B-29s main advantage over Germany rather than its altitude. Strategic bombing of ball-bearing industries, air-craft factories, perhaps even oil-fields and synthetic oil-factories is a pipe-dream from 10-11 km. altitude anyway.

I find it interesting that the B-29 was more vulnerable to flak than the B-17 and B-24.

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Post by Tony Williams » 19 Jan 2005 14:16

Lars wrote:
Tony Williams wrote:
There can be no doubt that before the advent of proximity-fuzed shells (which changed everything), the optimum solution for attacking large, high-flying bomber formations with AAA was to use sub-calibre, contact-fuzed shells.
Tony´s and von Shadewald´s solution (no time fuses) mens that the rate of fire goes up. BUT if it also means that the ammo expenditure goes through the roof (ratio of shells/each plane destroyed goes up), the Germans would actually be worse off as they simply couldn´t produce more shells.

You may have a point Tony and Shadewald, but you need to make it likely that the costs of bringing down a bomber would go down.
They would. The Germans discovered that fitting contact fuzes improved the kill probability. So although they may have fired more shells, the number of bombers hit would have gone up by a larger percentage. And on top of that, you are saving the cost of those intricate and expensive clockwork time fuzes (which also used up a lot of valuable aluminium alloy).

TW

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Post by Lars » 19 Jan 2005 15:43

In 1944 Flak accounted for 3,501 American planes destroyed, enemy fighters shot down about 600 less in the same time period. German Flak accounted for 50 of the 72 RAF bombers lost over Berlin on the night of March 24th, 1944. An incredible 56 bombers were destroyed or crippled by flak during a B-17 raid on Merseburg in November of 1944.

Now, I can understand that the RAF would suffer heavily over Berlin with its hordes of flak, but since I´ve never heard of the town of Merseburg before, 56 B-17s seems an awfull lot of casualties over such a minor taget. Perhaps the high losses over Merseburg in November 1944 was due to the new direct fire with no time-fuse?

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Post by Lars » 19 Jan 2005 17:37

Merseburg was a refinery and very heavily defended so the huge losses may have nothing to do with changed German shell fuses:

"This was the most dreaded of all targets! Intelligence reported that since our last raid, the Germans had moved 807 AAA (88mm) cannon, each fixed to fill its spot inside a cubic mile directly above the refinery in Merseburg! The intelligence officer added, "You will encounter the largest concentration of eighty-eight millimeter flak we've ever seen!" A meteorologist came to the podium and informed us that it would be clear and sunny over the target. Bombing would be from an altitude of 28,000 feet."

Merseburg was quite a drama. Here seen from a B-17:

http://www.flightjournal.com/articles/b ... ress_1.asp

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Post by Lars » 20 Jan 2005 10:54

Tony Williams wrote: The Germans discovered that fitting contact fuzes improved the kill probability. So although they may have fired more shells, the number of bombers hit would have gone up by a larger percentage. And on top of that, you are saving the cost of those intricate and expensive clockwork time fuzes (which also used up a lot of valuable aluminium alloy). TW
Aluminium was indeed a scarce metal for Germany. On top of that it took a lot of energy (coal) to convert bauxit to aluminum.

I find it truly immensely ironic that the Germans choose the round-about way to flak (time fuses) when the faster, more effective and cheeper way to keep the contact fuzes would have been better. Were they alone in this or did the Brits suffer from the same misconception?

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Post by Tony Williams » 20 Jan 2005 13:15

Lars wrote:I find it truly immensely ironic that the Germans choose the round-about way to flak (time fuses) when the faster, more effective and cheeper way to keep the contact fuzes would have been better. Were they alone in this or did the Brits suffer from the same misconception?
Everybody used time fuzes for larger-calibre AA guns, as far as I know. The break-point seemed to be around 40mm. The original RN 2 pdr (40mm) naval AA shells used time fuzes, but by WW2 these had been replaced with contact fuzes.

TW

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Post by Lars » 20 Jan 2005 13:28

Tony Williams wrote: Everybody used time fuzes for larger-calibre AA guns, as far as I know. The break-point seemed to be around 40mm.
Including Soviet AAA?

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Post by Tony Williams » 20 Jan 2005 13:34

Lars wrote:
Tony Williams wrote: Everybody used time fuzes for larger-calibre AA guns, as far as I know. The break-point seemed to be around 40mm.
Including Soviet AAA?
I have no definite information about WW2 practice. I know that the postwar 57mm shells are contact-fuzed only.

TW

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Post by Lars » 21 Jan 2005 15:00

Tony Williams wrote: The Germans discovered that fitting contact fuzes improved the kill probability. So although they may have fired more shells, the number of bombers hit would have gone up by a larger percentage. And on top of that, you are saving the cost of those intricate and expensive clockwork time fuzes (which also used up a lot of valuable aluminium alloy). TW
Bringing down the costs was paramount. Flak was EXTREMELY wasteful. As I mentioned, it took 3,343 shells costing a total of 267,440 reichsmarks ($107,000) to bring down one bomber. The production price of one V2 was 125,000 RM, and the production price of one V1 was 5,000 RM. For the price of bringing down one Allied bomber, the Germans could have produced two of the hideously expensive V2s, or 134 V1s 8O

Speer, or was it Milch, once said that one V2=3 or 4 ME 262s, so I guess you get the picture..

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