About aiming targets

[mentuhotp]

Hi everybody.
I have a question regarding this report of Operational Analysis Section of 15th Air Force. I'm not sure it's the right place for this post.
As you can see, a formation of 4 Boxes of B-24 Liberators ( 3 boxes of 8 A/C and 1 of 7A/C ) , bombed the target using the typical " 6 aircraft front " formation of 15th AF. Box A, B were the 1st AU ( Attacking Unit ), Box C,D were the 2nd one. In this case we had 4 Bombardiers : the Group Leader in Box A and 3 Box Leaders ( in Boxes B,C and D ). Every Box Leader aimed and dropped. The remainders of the Box dropped on the first.
My doubt is related to point 5. of this analysis : Method of Sighting. Somebody sighted for both Range and Deflection ( namely the 2 Leaders of the Attacking Units, so A and C ), others only for Range ( again the 2 Leaders of the Attacking Units ?? and the single Box Leaders ). What does it mean? It's confusing.
First: if the 2 Leaders of the Attacking Units sighted for both Range and Deflection how could they sight for Range only at the same time?
Second: every Box Leader sighted for Range. But why didn't sight for Deflection too? Maybe they dropped on the AU Leader ? But, if so, why sight for Range ?
The same scheme is typical of every report of this type I read ( hundreds ).
Thank You for your opinions.
Fausto

 

[MiTasol]

Somewhere on this forum is a copy of the USAAF Bombardiers Information File. That will probably have the answer

 

[fubar57]

Bombardiers' Information File : United States. Army Air Forces. Office of Flying Safety : Free Download, Borrow, and Streaming : Internet Archive

March 1945 edition of Bombardiers' Information File BIF 1-6-3.When you receive BIF revisions you are required by AAF Regulations 62-15 and 15-24 to do the...

archive.org

 

[mentuhotp]

Thank You.
I've got that book but it concerns the general bombing technique. My question is about a " tactic " developed by a specific Force as a result of its experiences on the field.

 

[Geoffrey Sinclair]

Look at page 8-6-1 of the Information File. It was a tactic used by many US day bomber units.

I doubt the diagram is to scale. The difference between aiming is because of the need to stay in formation, if every aircraft starts moving to line up with the target the formation will break and the collision risk goes way up. The solution became leader does a "full" sighting, the immediate formation drops when the leader does, the nearby formations drop when their leader's sight says correct range. Repeat depending on the raid size. The nearby formations will up their risks of collision or hitting the slipstreams of the leaders if they start moving for deflection, that is changing course. The method was more accurate than individual sighting.

As a measure of the differences between reports on the same raid, the bombing accuracy sheet says 31 aircraft at 14,500 feet with 2x2000 pound RDX or 5x1,000 pound RDX, time 1112, Ceiling and Visibility Unlimited CAVU. When the 15th Air Force compiled its report that became 31 aircraft at 14,100 feet dropping 42x2000 pound GP and another 24.5 short tons of bombs, type not listed, presumably 49x1000 pound, so 21 aircraft with 2x2000 pound and 10 with 5x1000 pound with 1 hang up or short load. Time 1112, weather poor. Altitude and time will depend on which sub formation you select, bomb types and visibility are another matter. There would be small but real differences between movements of the bombers dropping 2 short tons and those dropping 2.5 short tons.

The 460th was also hitting the target with 30 aircraft at 1113 from 13,500 feet in poor weather dropping 60 tons of bombs, 32x2000 pound GP, 18x2000 pound RDX and 22x1000 pound GP, which comes to 61 tons, plus another 2.5 tons were jettisoned, no reason given.

 

[mentuhotp]

The difference between aiming is because of the need to stay in formation, if every aircraft starts moving to line up with the target the formation will break and the collision risk goes way up. The solution became leader does a "full" sighting, the immediate formation drops when the leader does, the nearby formations drop when their leader's sight says correct range. Repeat depending on the raid size. The nearby formations will up their risks of collision or hitting the slipstreams of the leaders if they start moving for deflection, that is changing course. The method was more accurate than individual sighting.

Thank You Geoffrey.

So Able ( the Group Leader and Leader of the first Attacking Unit ) sighted for both range and deflection. The same did Charlie, Leader of the second Attacking Unit, because he flew behind Able and their routes didn't interfere. Baker and Dog, which flew on the right of the previous, sighted only for range, cause sighting for deflection would have caused their collision with the other two boxes.
In this way, if Able and Charlie would have released with precision, Baker and Dog would have for certain missed the target. Probably A and C bombed sligthly off-center on the left to allow B and D to place some bombs on the target and the others on the right of it.

I still don't understand the statement on the report that the AU Leaders sighted at the same time for "range and deflection" ( as in the upper line ) and for "range only" ( as in the line below ). Maybe that sight for "range" is simply redundant . . .

 

[Geoffrey Sinclair]

So Able ( the Group Leader and Leader of the first Attacking Unit ) sighted for both range and deflection. The same did Charlie, Leader of the second Attacking Unit, because he flew behind Able and their routes didn't interfere. Baker and Dog, which flew on the right of the previous, sighted only for range, cause sighting for deflection would have caused their collision with the other two boxes.
In this way, if Able and Charlie would have released with precision, Baker and Dog would have for certain missed the target. Probably A and C bombed sligthly off-center on the left to allow B and D to place some bombs on the target and the others on the right of it.

I doubt the idea was to certainly miss the target. Remember the diagram is not to scale, we have no idea of the distances between the formations, or the different heights, if the second pair of formations were exactly behind the first at the same altitude they would be badly affected by the slipstream, so they must have been at least at different altitudes. We also do not know whether the bomber course was parallel to the bridge, at right angles or somewhere in between. Then add there were another 30 bombers from a different group in the same airspace.

I still don't understand the statement on the report that the AU Leaders sighted at the same time for "range and deflection" ( as in the upper line ) and for "range only" ( as in the line below ). Maybe that sight for "range" is simply redundant . . .

Agreed the entries are confusing.

 

[mentuhotp]

I doubt the idea was to certainly miss the target.

Yes Geoffrey, the "six aircraft front bombing formation", as compared with the "train of boxes" formation, could completely miss the target. See below from 1945 "Air Operations Briefs" : Formations in the Fifteen ".

The Boxes were stacked down with 200 to 300 feet difference in altitude. Each Box in trail was spaced of 500 to 1000 feet.

A bridge was usually attacked with an angle from 30 to 45 degrees.

 

[JDCAVE]

Yes Geoffrey, the "six aircraft front bombing formation", as compared with the "train of boxes" formation, could completely miss the target. See below from 1945 "Air Operations Briefs" : Formations in the Fifteen ".

The Boxes were stacked down with 200 to 300 feet difference in altitude. Each Box in trail was spaced of 500 to 1000 feet.

A bridge was usually attacked with an angle from 30 to 45 degrees.View attachment 719488View attachment 719489

The issue is: was this radar bombing or visually. It’s not clear to me from the foregoing posts. The comment “weather poor” does not align with visually identifying the target, but I stand to be corrected. If bombing by H2X, the bombing may have been “highly precise” but at the same time “highly inaccurate”

Jim

 

[mentuhotp]

Hi Jim.
This target was identified visually. See the report:

Note that there was only one H2X t for Group in 15th AF, that of Lead Bombardier plane and, if the bombing was done by PFF, usually nobody else of the group sighted.

 

[Geoffrey Sinclair]

Most bombs did miss, my point was the USAAF not setting up to deliberately miss. Where do the bomber reports come from? And do they have fighter and reconnaissance operations?

Not sure what the H2X comment is about. As of 2 September 1944 the 15th AF B-17 groups held 7 to 9 pathfinder B-17, all up 289 B-17G to 47 PB-17G, the B-24 groups were further behind, 699 bomber to 71 pathfinder with 3 to 6 pathfinders in each B-24 group. By the end of the month it was 879 bomber to 60 pathfinder, 2 to 6 per group. The 465th had 3 PB-24H and 1 PB-24J on 2 September plus 57 B-24, then 3 PB-24H plus 61 B-24 on 30 September. Visual bombing was preferred, as I understand things if there was enough cloud around the bomb run assumed dropping by radar but kept the option of using visual if there was a break in the clouds.

 

[mentuhotp]

I didn't mean that they deliberately miss but that they created a pattern in width just as they created one in lenght with the use of intervallometer: it increased the possibility that the central bombs hit the target, while the first and last obviously failed. Similarly, for 6 nearly paired aircraft attacking, with only the second from left ( the Attacking Unit Leader ) sighting the for range and deflection, I wonder how it was possible for n. 4,5,6 from left to hit the target. I think that the AU Leader aimed a bit left of the target to allow at least n 3 and 4 to hit in the center, while the others probably hit too left and too right. But this is only my opinion.

What I know for certain is that, although there were many PFF ships assigned to a Group, only one leaded the Group in a mission. A second ship could be employed if the Group was splitted to attack two different targets, but it was non common.
About B-17 of 15th AF, see for example of this report of 301st PFF. There is only one PFF operator and only one PFF bombardier.

The source of all my knowledge are the records of NARA and AFHRA.

 

[buffnut453]

I don't meant that they deliberately miss but that they created a pattern in width just as they created one in lenght with the use of intervallometer: it increased the possibility that the central bombs hit the target, while the first and last obviously failed. Similarly, for 6 nearly paired aircraft attacking, with only the second from left ( the Attacking Unit Leader ) sighting the for range and deflection, I wonder how it was possible for n. 4,5,6 from left to hit the target. I think that the AU Leader aimed a bit left of the target to allow at least n 3 and 4 to hit in the center, while the others probably hit too left and too right. But this is only my opinion.

It wasn't that precise. The bombs themselves had poor ballistic characteristics and could spear off in any number of directions. Making fine adjustments to the left or right of the aim point didn't make a lot of difference in the probability of hitting the target.

Just look at the different angles these bombs are pointing.

Incendiaries were particularly bad, having appalling ballistic characteristics:

One more and then I'll quit:

 

[33k in the air]

It wasn't that precise. The bombs themselves had poor ballistic characteristics and could spear off in any number of directions. Making fine adjustments to the left or right of the aim point didn't make a lot of difference in the probability of hitting the target.

Just look at the different angles these bombs are pointing.

View attachment 720299


Incendiaries were particularly bad, having appalling ballistic characteristics:

View attachment 720300


One more and then I'll quit:

View attachment 720301

That first photo with the B-17s, those bombs are almost certainly 100-lb class based on the number being released, in which case they're either the AN-M30 GP or the AN-M47 incendiary. (The B-17, using cluster adapters, could carry 38 of the GP bombs or 42 of the incendiary.) The two photos with the B-29s, based on the number of bombs being dropped, are again either the 100-lb AN-M30 GP or AN-M47 incendiary, most likely the latter. (Using cluster adapters, the B-29 could carry up to 184 of the incendiary.)


Below is a graph showing the trajectories of various incendiary bombs and clusters, along with a couple of GP bombs for comparison. The notably smaller dispersal area of the aimable cluster using the 4-lb incendiary versus the quick-opening cluster is readily apparent. (Source: Fire Warfare — Incendiaries and Flame Throwers, Summary Technical Report of Division 11, NDRC, Volume 3, p.17)

From the same source (p.51), a table showing the results from a formation drop of AN-M47 incendiary bombs.

Lastly, from the same source (p.52) a graph plotting the dispersal of incendiary bombs from a single aimable M18 cluster (38 x 6-lb AN-M69).

The smaller incendiary bombs were always area weapons, given their light weight resulted in them being easily dispersed.


ETA: the source document can be downloaded from the Bullet Picker website. It's found in the Library section under 'US Government', fourth from the bottom in the list. It can also be found at the Japan Air Raids.org website, under Documents > English Language Documents > Incendiary Weapons.

 

[Geoffrey Sinclair]

I didn't mean that they deliberately miss but that they created a pattern in width just as they created one in lenght with the use of intervallometer: it increased the possibility that the central bombs hit the target, while the first and last obviously failed. Similarly, for 6 nearly paired aircraft attacking, with only the second from left ( the Attacking Unit Leader ) sighting the for range and deflection, I wonder how it was possible for n. 4,5,6 from left to hit the target. I think that the AU Leader aimed a bit left of the target to allow at least n 3 and 4 to hit in the center, while the others probably hit too left and too right. But this is only my opinion.

As others have pointed out the bomb ballistics come into play and the reality of mass produced weapons. When the 509th Composite Group began its training it discovered in the final moments a movement by the bombardier of a couple of inches as he readied to drop made a difference of hundreds of feet to where the bomb landed. The USSBS did a major report on bombing accuracy, noting how errors went up with altitude and size of raid.

Apart from the ballistics there is how accurate the wind drift and altitude measurements were, how aligned the sight was, how correctly it was set up and so on. All the bombers were moving on slightly different courses at slightly different speeds and altitudes. Also remember by deliberately being at different altitudes the other formations dropping on the leader could compensate for distance. If everything was right then the formation that had the aimer should score the most hits. Instead the errors in the aiming system meant it was quite possible for everyone to miss.

What I know for certain is that, although there were many PFF ships assigned to a Group, only one leaded the Group in a mission. A second ship could be employed if the Group was splitted to attack two different targets, but it was non common.

If the group only had 1 PFF aircraft airborne then it was single point of failure, if the H2X set failed or the aircraft had a defect, or was damaged or shot down, then the mission was in trouble. There should have been at least a backup PFF aircraft. Also why have so many PFF aircraft in a group if only 1 was needed on a mission? On 31 March 1945 the strength in groups was 77 PB-17 to 307 B-17 and 176 PB-24 to 690 B-24 or about 1 in 5 were pathfinders.

Consider the possibility the reports in the files are from the PFF aircraft used, as the entire group (including any other PFF aircraft) dropped with it.

About B-17 of 15th AF, see for example of this report of 301st PFF. There is only one PFF operator and only one PFF bombardier. The source of all my knowledge are the records of NARA and AFHRA.

I understand that, I was after file references. The example given is an AFHRA file, like

AFHRA 670.308-3, 15th AF Target and Duty sheets Dec 43 to Feb 44 (incomplete)
AFHRA 670.308-4, 15th AF Daily/Monthly statistics March to October 1944

US Archives, Record Group 18 Entry 7, Boxes 5927 (Apr-44), 5928 (Aug,Sep-44), 5939 (Jun,Jul-44), 5940 (Dec-43 to Mar 44, May and Oct 44) Target and Duty Sheets, 15th Air Force.

As AFHRA now restrict requests to 5 per month I was hoping someone might already have the fighter and reconnaissance data for the months I am missing, November and December 1944, February and May 1945, instead of me needing to wait a couple of months for the files, or could tell me which files to ask for instead of needing to pick them from the titles with the risk of the information not being in the file.

 

[buffnut453]

That first photo with the B-17s, those bombs are almost certainly 100-lb class based on the number being released, in which case they're either the AN-M30 GP or the AN-M47 incendiary. (The B-17, using cluster adapters, could carry 38 of the GP bombs or 42 of the incendiary.) The two photos with the B-29s, based on the number of bombs being dropped, are again either the 100-lb AN-M30 GP or AN-M47 incendiary, most likely the latter. (Using cluster adapters, the B-29 could carry up to 184 of the incendiary.)


Below is a graph showing the trajectories of various incendiary bombs and clusters, along with a couple of GP bombs for comparison. The notably smaller dispersal area of the aimable cluster using the 4-lb incendiary versus the quick-opening cluster is readily apparent. (Source: Fire Warfare — Incendiaries and Flame Throwers, Summary Technical Report of Division 11, NDRC, Volume 3, p.17)

View attachment 720313


From the same source (p.51), a table showing the results from a formation drop of AN-M47 incendiary bombs.

View attachment 720315


Lastly, from the same source (p.52) a graph plotting the dispersal of incendiary bombs from a single aimable M18 cluster (38 x 6-lb AN-M69).

View attachment 720316


The smaller incendiary bombs were always area weapons, given their light weight resulted in them being easily dispersed.


ETA: the source document can be downloaded from the Bullet Picker website. It's found in the Library section under 'US Government', fourth from the bottom in the list. It can also be found at the Japan Air Raids.org website, under Documents > English Language Documents > Incendiary Weapons.

Agree with everything you're saying, and smaller, lighter incendiaries are inherently more susceptible to dispersion from higher altitude. However, my general point remains. Even slight damage to the fin structure of a 500lb bomb will impact its trajectory...and there are plenty of images showing bombs being rolled over the ground and other similar practices that are likely to ding the fins. And that's before we consider subtle dimensional differences in the bomb shape itself that may alter its ballistic trajectory.

 

[mcoffee]

Thank You Geoffrey.

So Able ( the Group Leader and Leader of the first Attacking Unit ) sighted for both range and deflection. The same did Charlie, Leader of the second Attacking Unit, because he flew behind Able and their routes didn't interfere. Baker and Dog, which flew on the right of the previous, sighted only for range, cause sighting for deflection would have caused their collision with the other two boxes.
In this way, if Able and Charlie would have released with precision, Baker and Dog would have for certain missed the target. Probably A and C bombed sligthly off-center on the left to allow B and D to place some bombs on the target and the others on the right of it.

I still don't understand the statement on the report that the AU Leaders sighted at the same time for "range and deflection" ( as in the upper line ) and for "range only" ( as in the line below ). Maybe that sight for "range" is simply redundant . . .

The A-2 and B-2 boxes (your c and d) cruised to the right but moved into trail for the attack so offset was not necessary. The 449th BG was tasked a different bridge on 23 Sep but did not bomb as both the primary and secondary targets were completely undercast. See the attached attack sheet and formation plan.

 

[mcoffee]

What I know for certain is that, although there were many PFF ships assigned to a Group, only one leaded the Group in a mission. A second ship could be employed if the Group was splitted to attack two different targets, but it was non common.
About B-17 of 15th AF, see for example of this report of 301st PFF. There is only one PFF operator and only one PFF bombardier.

The source of all my knowledge are the records of NARA and AFHRA.

Depended on the target. The previously attached formation plan has a Mickey Ship (PFF) at A-1-1 and B-1-1. In the formation plan attached here A-1-1, B-1-1, B-2-1, and C-1-1 are all PFF. The names with MN preceding are the "Mickey Navigators" . B-24 Lead ships carried 3 navigators: normal navigator, Mickey navigator and a navigator manning the nose turret to aid with pilotage nav. Later in the war, the deputy leads (A-1-2, etc.) would also be PFF ships on missions where PFF navigation or bombing was likely.

 

[mentuhotp]

The A-2 and B-2 boxes (your c and d) cruised to the right but moved into trail for the attack so offset was not necessary. The 449th BG was tasked a different bridge on 23 Sep but did not bomb as both the primary and secondary targets were completely undercast. See the attached attack sheet and formation plan.

Not always and not in this case. The "train of boxes " was not the rule( the longer the train, the happier the FLAK ). In the "6 air front formation" the position of boxes could be the same in cruising and bombing. In the sheet to which my original question referred is clearly said "bombing formation".

Consider the possibility the reports in the files are from the PFF aircraft used, as the entire group (including any other PFF aircraft) dropped with it.

Yes, of course. I told that only one PFF leaded the Group and aimed during the bombing run. The spares were inactive unless malfuctions or alternate targets needed their intervention.

 

[33k in the air]

Agree with everything you're saying, and smaller, lighter incendiaries are inherently more susceptible to dispersion from higher altitude. However, my general point remains. Even slight damage to the fin structure of a 500lb bomb will impact its trajectory...and there are plenty of images showing bombs being rolled over the ground and other similar practices that are likely to ding the fins. And that's before we consider subtle dimensional differences in the bomb shape itself that may alter its ballistic trajectory.

There is also the matter of duds, which applied to both high explosive and cluster bombs.

The USSBS Oil Division report stated that 1.8% of bombs which fell in the target area failed to explode — but only 12.9% of bombs dropped fell in the target area, and the number which fell outside the target area and failed to explode wasn't recorded. This implies an overall dud rate of almost 14%, or about 1 bomb in 7 failing for one reason or another. (Tails separating from the bomb during its descent seems to have been a frequent occurrence.)

The source I mentioned earlier has a table showing the results of drops of the M19 aimable cluster (p.16). From those dropped from 10,000 feet, the percentage which failed to operate correctly ranged from 2.7% to 4.9%; from 15,000 feet, 2.4% to 3.4%; and from 30,000 feet, 6% failed for one reason or another.

The British also had issues with dud bombs.