Bombing theory, technology and techniques

[wuzak]

I wanted to start a thread discussing the different theories, technologies and tactics involved in bombing during WW2 and how these translated into reality.

It is quite interesting how the technology developed during WW2, especially the electronic bombing aids, but these would have their limitations too.

 

[wuzak]

Comparison between low and high altitude visual marking on defended targets at night

From mid war the RAF started using pathfinders to imrpove the accuracy of their bombing. They developed target indicators (TIs) to illuminate the aiming point, developed electronic aids to help with navigation to the target and even set the release point for TIs or bombs.

In 1945 the Operational Research Section (ORS) evaluated visual target marking at night from low and high altitudes in the period of July 1944 to January 1945.

In both cases the target area was illuminated by H2S aircraft dropping flares.
Target markers would then visually aim their TIs on the target and releas them. Secondary markers (centerers) would be called in to adjust the marking. This would all be controlled by the Master Bomber.

if visibility was insufficient then the marking would be done using blind bombing techniques (ie H2S).

The success of the bombing mission relied on the accuracy of the target marking.

The two techniques used were:
High Level Marking: Marking was performed by Lancasters in level flight with a release altitude of between 11,000ft and 18,000ft. Aiming would be via the Mk XIV bomb sight. 250lb TIs or 1,000lb TIs would be used. The TIs woudl burst at around 4,000ft. 3 - 8 TIs would be released in a stick. Bewteen 2 and 7 markeing aircraft would be used on each operation.

This was the technique that 8 Group would use.

Low Level Marking: Marking was done by a Mosquito in a shallow dive from around 4,000ft, relese point at between 600ft and 2,000ft. Aiming was done by the pilot, normally without a sight. Some aircraft did use a Standard Turret Reflector Gun Sight GJ Mk III for aiming. 1,000lb TIs were used, generally, being released individually. The TIs would burst at between 400ft and 1,000ft. 4 - 9 markers would be sent on each operation.

The low level marking technique was pioneered by Wing Commander Leonard Cheshire, commander of 617 Squadron after Gibson was promoted.

The plots of TIs could be ascribed to individual aircarft in the case of the high level marking, but not for low level marking. Using pilot's notes the error in line and range could be calculated for high level marking, but not for low level marking.

The report mentions that a correction factor was applied to account for windage erros - 150 yds for high level marking and 35 yards for low level marking. This gives an aiming error of 888 yards for high level marking and 274 yards for low level marking.

In clear conditions the marking was reliable for both methods. But when cloud was a factor the reliability of high level visual marking reduced, while the reliability of low level marking remained the same.

The choice or marking point was important as it needed to be easily identifiable at night.

The low-level marking used an offset marking technique, which offered more marking points. The main bombing force would then bomb in a certain heading releasing a set period after the marking point.

The high level markers generally dropped on the actual aiming point, the main force bombers aiming directly at the markers.

While the report selected targets that were classified as "heavily defended", there were still variations in the level of defences which definitely affected aiming accuracy.

The loss rates of target markers were similar, with low-level markers having a higher loss rate. But since the sample size was small, it is doubtful conclusions could be drawn.

Master Bombers fared less well. In high level marking the Master Bomber loss rate was 2.44% while for low level marking it was 9.80%.

In the case of the high level raid, the Master Bomber is a visual marker himself. For the low level markers the Master Bomber does not, instead directing and correcting the marking while orbiting the area. In both cases teh MAster Bomber remains in the area longer than the marking aircraft.

These plots graphically show the difference in the accuracy of the techniques.

The conclusion was that the low level visual marking technique held the advantages of higher reliability and greater accuracy than the high altitude method. There was some question over the low level method would be viable in a very heavily defended target, such as those found in the Ruhr.

And the other major downsied was the limited numbers of TIs the marker aircraft could carry. In the Mosquito a maximum of 2 x 1,000lb TIs or 4 x 250lbs could be carried.

 

[stona]

Target markers would then visually aim their TIs on the target and releas them. Secondary markers (centerers) would be called in to adjust the marking. This would all be controlled by the Master Bomber.

And the other major downsied was the limited numbers of TIs the marker aircraft could carry. In the Mosquito a maximum of 2 x 1,000lb TIs or 4 x 250lbs could be carried.

Once the marking was deemed complete the master bomber would call on an aircraft flying at a similar altitude to the incoming main force to check the visibility of the markers. The conversation between the master bomber and this aircraft on the Dresden raid was recorded.
The master bomber's call sign was 'Controller' and the checking aircraft 'Check 3'. Check 3 was a Lancaster of No. 97 Squadron, orbiting at 18,000 feet.

Controller to Check 3: Can you see the glow? over

Check 3 to Controller: I can see three TIs through cloud. Over.

Controller to Check 3: Good work. Can you see the reds yet? Over.

Check 3 to Controller: Can just see reds. Over.

The master bomber had a brief discussion with the remaining marker aircraft, ordering them to drop any remaining flares and markers before 'getting out'.

Controller to Check 3: Can you see the red TIs ? Over

Check 3 to Controller: Can see green and red TIs. Over

Controller to Check 3: Thank you.

With visible and accurate markers confirmed the master bomber now communicated with the 244 Lancasters of 5 Group, code named 'Plate Rack Force'.

Controller to Plate Rack Force: Come in and bomb glow of red TI as planned. Bomb glow of the red TIs as planned.

The rest as they say, is history.

Cheers

Steve

 

[fubar57]

Good stuff gentlemen. Steve, were the colour call outs to make sure the Germans weren't laying decoys? (I hope you know who doesn't see this)

 

[stona]

were the colour call outs to make sure the Germans weren't laying decoys?

That was the original reason for different coloured TIs. You'll notice that the master bomber asked the main force to bomb the red TIs 'as planned', so red was always the colour to be used as the primary ground marking for 5 Group on this raid.
Earlier in the war the Germans had used decoy sites quite effectively.
Cheers
Steve

 

[wuzak]

Wanganui and Paramatta

Wanganui and Paramatta were two marking methods developed and used by the RAF during WW2. These were marking using blind bombing techniques, either Oboe, H2S or, possibly, dead reckoning. When Oboe was used the prefix Musical was added to the codename.

The visual marking methods, as described above, were codenamed Newhaven.

Paramatta was the system where ground marking was achieved with blind bombing systems.

Wanganui was sky marking using blind bombing systems.

Paramatta was easier to use, presumably for both markers and bombers. But its limitation was the level of cloud over the target area, as ground markers could often be obscured.

Thus the recommendation was for marking aircraft to have both types available.

The height at which sky markers were set to burst depended on the altitude of the clouds. And this could be a problem for the following bombers.

It was observed that the German flak gunners or their command quickly learned what the purpose of the sky marker flares was. Consequently they would set their flak concentration about the position and altitude of the released flares. This could be a particular problem if the flares were set to burst not much below the set bombing height, as each bombing aircraft would be in the region of the flare when they released their bombs.

The counter-measure to this was that the TIs would be set to burst at the lowest possible altitude. That did require accurate cloud information. The positive is that when the cloud base was so thick as to require the burst point near the release altitude it was thought that the flares would be difficult to be seen from the ground, and thus targeting less accurate.

Because the sky markers would naturally fall as time went by, the course, speed and timing of the bombing attacks was critical.

Before the main flares were dropped, a warning flare was dropped and set to burst at a set time. This would enable crews to ensure that they were lined up on the correct course for the bomb run,

At the appointed time the marker flares would be dropped. Crews were then instructed to bomb when the flares were within their bomb sights.

When the flares were extinguished or fell from view a secondary marker would be dropped. This would differ in colour from the main target flares. As this was considered to be less accurate than the initial markers corrections were added.

Flares were observed to burn for approximately 4 minutes. Originally this was thought to e 2 minutes. The ideal time for bombing was, therefore, 2 minutes after the flare ignited.

Bombs released when the flare was in the bomb sight were found to be of reasonable accuracy - that is, within 2 3/4 miles of the aiming point.

An interesting point made in the reports I have is that bombing in Lancasters at altitudes of 20,000-22,000ft allows only gentle evasive manoeuvres to be performed without losing height, while it was found that speeds above 145-150mph IAS were difficult to maintain without losing height.

Crews were asked to fill out a questionnaire upon returning to base:

 

[wuzak]

A sample response to the questionnaire:

Nil seems to have been a popular response to question 12.

 

[stona]

A sample response to the questionnaire:
Nil seems to have been a popular response to question 12.

Excellent stuff. This is the basis of the information that went into the 'diagram' that described the raid graphically and was produced for every raid.

As to question 12, why write anything that could lead to more questions from an intelligence officer when all you wanted was breakfast and bed ?!

Bombing techniques broken down into stages:

SHAKER (the earliest system, before target marking pyrotechnics were developed, and from which all the others developed. It was a means of attempting to exploit the first really useful navigational aid, GEE)
1. 'Illuminators' drop flares
2. 'Finders' drop incendiaries to confirm target.
3. 'Followers' bomb on incendiaries.

NEWHAVEN
1. Flares dropped by Pathfinder Force using H2S or Oboe (Musical Newhaven).
2. Second wave of Pathfinder Force aircraft drop Target Indicators visually using the light from the flares.
3. Main Force bomb on Target Indicators.

PARAMATTA
1.Pathfinder Force drop target Indicators blind using H2S or Oboe (Musical Paramatta).
2. Main Force Bombs on Target Indicators.

WANGANUI
1. Pathfinder Force drops parachute Target Indicators using H2S or Oboe (Musical Paramatta). This is a sky marking technique well described in the previous post. The point of release would consider the wind conditions to allow for drift.
2. Main Force bombs on TIs.

This is just the bare bones of each system. There were many variations on these themes. For example, the marking would almost always be backed up as the raid proceeded by designated 'backers up'. The master bomber could adjust the marking as he saw fit. It was not always the target itself which was marked. 5 Group in particular developed a system of 'timed run' in which aircraft made a timed run in to the target from a position marked some distance away and therefore less likely to be obscured by the bombing. This evolved into 'sector bombing', in which each aircraft of a squadron flew a timed run to the target from a distant marker on a slightly different heading (usually 2 degrees) and run time. The result was bombing an area something like a slice of cake.

Cheers

Steve

 

[JDCAVE]

I'm coming in late on this thread. Wuzak: from the notes in your first thread, it would seem that this pertained to 5-Group, as it discusses low level marking by Lancasters and low level marking by Mosquitos-correct? Could you please provide the AIR file number for this report? I would definately like to see the report in full.

I am researching the "Blind Marking" and "Blind Illuminating" procedures by 8-Group during the final months of the war. One of the Form "B"'s I have refers to the "Y" method, which from the notes in the Form, relates to the use of Radar, which makes sense.

I have found a reference to a report by ORS entitled: "H2S Blind Bombing, Illuminating and Marking accuracy October 1944-April 1945."

...it's a "Hail Mary", I realize, but if anyone has it, I would really like to see it.

I have a couple of Docs from the 8-Group ORB Appendices, March 1945. The Group was using H2S Mark III, which was a 3 Centimetric Radar. These are in the Navigation section:

Jim

 

[wuzak]

I'm coming in late on this thread. Wuzak: from the notes in your first thread, it would seem that this pertained to 5-Group, as it discusses low level marking by Lancasters and low level marking by Mosquitos-correct? Could you please provide the AIR file number for this report? I would definately like to see the report in full.

Jim, the report pertained to both high level marking by Lancasters and low altitude marking by Mosquitoes, and was comparing the two.

I will get the report number for you later.

 

[wuzak]

Jim, the report is:

AIR 14-4538 - A comparison of high and low-level visual marking on defended targets at night

You may also be interested in:

AIR 14-2029 - Wanganui and Paramatta blind bombing techniques methods operational procedure

 

[EwenS]

The Pathfinder Mosquito squadrons had their own specialisms.

109 - began testing Oboe in July 1942, flying its first operational Oboe op on 20 Dec 1942. Early Oboe equipment gave good results to a range of 275 miles at 28,000ft. Initially using B.IV aircraft, B.IX arrived in May 1943 allowing increased range as the new aircraft could reach 30,000ft.

105 - became the second Oboe squadron, flying its first Oboe mission on 9 July 1943.

Mark B.XVI arrived on the squadrons in Dec 1943. While the range of Oboe was improved over time, it was April 1945 before new equipment allowed Berlin to be reached.

139 - pioneered the use of G-H for blind bombing. Introduced in Oct 1943 (first successful use 10/11 Oct). It then went on to pioneer use of H2S in Mosquitos from Jan 1944, initially in Mk.IV and then Mk.XVI from March 1944 by which point about half its aircraft were so equipped. H2S equipped Mosquitos were referred to as 'Y' aircraft.

162 - formed in Dec 1944, it began working up with H2S in Feb 1945, and flew its first marker mission on 3 March 1945.

617 - used a handful of Mosquitos for low level marking between April & Aug 1944, including Mk.IV, Mk.VI and Mk.XVI.

627 - formed in Nov 1943 from a nucleus provided by 139 squadron. It was part of the Light Night Striking Force in 8 (Pathfinder) Group until transferred to 5 Group in April 1944. They then specialised in low level marking for 5 Group, including 617.

 

[wuzak]

Edit: Posted in wrong thread.