Stukas and HMS Illustrious.

[Birgir Thorisson]

Esteemed Stuka- experts on this forum

I turn to you to clarify what excactly hit HMS Illustrious on January 10th 1941. I have tried to search the forum, but cannot find anything on these events.

There is a long-standing disagreement, among those interested in naval warfare, about the value of the british armoured carriers of the Illustrious class.
The argument centers on the survivability of armour, versus the defence offered by a larger airgroup of modern fighters.

The most important example to the defenders of the armoured (box) carriers is the survival of HMS Illustrious in January 1941.

However, I am finding conflicting data about what happened. The standard account is that it was hit by 6-8 bombs, mostly 500 kg armour piercing bombs, maybe 1-2 250 kg SAP bombs. (The official record is 10 550kg bombs, (D.K. Brown, Nelson to Vanguard, p.205), but on p.51 he says 7 hits, probably 500kg.)
That the attack on jan. 10th was carried out by 50-100 Stukas of I. StG 1 and II. StG 2.

Paul-Werner Hözzel, Kommandeur I. StG 1, wrote an account for Charles Lamb, published in "War in a Stringbag". He differs in two respects from the "standard account". A) He only arrived on january 13th, and therefore did not take part in the Jan.10th attack, and B) that in later attacks on Illustrious in Valetta harbour, the Stukas carried 1000 kg bombs, which broke up on the armour.

However. I recall reading an account by a former Stuka ace in a british aviation magazine about a decade ago, where he claimed that the heavy bombs were reserved for the battleships, and Illustrious was attacked by planes carrying the 250 kg bombs. Unfortunately, I didn´t buy the magazine, so I don´t have it, and don´t recall other details.

The questions I have are;
1) How many Stukas attacked on January 10th.?
2) What kind of bombs did they carry?
3) How many were Ju 87B and how many Ju 87R?
4) Could the Ju 87R carry 500kg bombs?
5) Could the Ju 87 carry 1000kg bombs?
6) Could the Ju 87B trade off bombload for range. (i.e. carry external drop tanks?) (This question because of the claim that the Germans knew that Illustrious was armoured, and therefore had to be attacked by 500kg AP bombs, thus reducing the range at which Stukas could attack, in a round-about way, creating a sort of an immunity zone for the carriers).
7). How long would it take the Stukas to arrive over the carrier at attacking height (I have seen both 12000 feet and 16000 feet mentioned), from the moment the incoming strike was detected on Radar?
(Both the Illustrious, and the battleship HMS Valiant had radars?
8) What was the radius of action of the Stuka? (Was it greater than the Bf 109?)

The last two questions pertain to the value of shipborn interceptors as an alternative defence for the ship.


Birgir Thorisson

[Juha]

Hello Birgir
I'm not a Ju 87 expert but some info
43 Stukas attacked, both Bs and Rs but I have not info how many were Bs and how many Rs.
identified bombs were 500kg
R could carry a 500 kg bomb
According to an article in Oct 1984 Air International, B-2 could carry a 1000kg bomb as single-seater, ie when WO/AG was left out.
IIRC of the pre-D types only Cs and Rs had capacity to use drop tanks.

HTH
Juha

[Birgir Thorisson]

Thank you Juha for your response.

I have the said article, and it is there that I picked up the info-snippet that the R could only carry one 250 kg bomb.("resticted to a maximum offensive load" of 250 kg. Closer look shows that it is in fact said about the R-1 model, but the R-2 is said to have primarily differed in installed equipment.

On the other hand, there is no logical explanation of why the R should be structurally limited to carrying only the 250 kg bomb. After all, you ought always to be able to trade off one form of payload (fuel) for another (bombs). But in that case, the R should be even shorter ranging than the B-2, which the article credits with 595 km max range, which should equate a radius of action of ca. 200 km, using the 1/3 rule of thumb.

There is no data on economica cruise speed, but using continous max cruise, (ca 300 km/h) with radar range of 100 km. (I don´t have it for the radar installed in Illustrious and Valiant), 20 minutes warning time would have been available for the carrier, before the Stukas were overhead. Which would, or would not, have been sufficent to scramble fighters, depending on the state of the organization onboard the carrier. (It would have been enough for the US at Coral Sea, but that is a different story.).

Birgir Thorisson

[Juha]

Hello Birgir
I don't have time to check but IIRC Rs could carry only a 250kg bomb if they had the drop tanks but were able to carry a 500kg if not burdened with drop tanks.

Juha

[Juha]

Hello Birgir
I read again Your message #3, and IIRC R had also bigger internal fuel tankage than B. And on 11.1. Stukas attacked RN CLs (IIRC HMS Southampton and HMS Glouchester plus some others) some 300 mls from Sicily, then they carried 250kg bombs.

Juha

[Nick Beale]

Originally Posted by Birgir Thorisson

On the other hand, there is no logical explanation of why the R should be structurally limited to carrying only the 250 kg bomb.
Birgir Thorisson

Just a thought but what about the crutch that swung the bomb outside the airscrew arc when dive-bombing? Might not the strength of that be a limitation?

[leonventer]

Hi Birgir,

Originally Posted by Birgir Thorisson

4) Could the Ju 87R carry 500kg bombs?
5) Could the Ju 87 carry 1000kg bombs?
6) Could the Ju 87B trade off bombload for range. (i.e. carry external drop tanks?)
7). How long would it take the Stukas to arrive over the carrier at attacking height (I have seen both 12000 feet and 16000 feet mentioned), from the moment the incoming strike was detected on Radar?
8) What was the radius of action of the Stuka?

Back in Feb 2002, Les Whitehouse submitted the three posts below about the differences between the Ju 87 B and R variants.

Hope that helps,
Leon Venter

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Ju87R - Les Whitehouse 13 Feb 2002
The reason for the classification of B-1 = R-1 and B-2 = R-2 was probably based upon engine. In actual fact the two types B-2/R-2 were built in parallel on the production lines at Weser only a few being later conversions so the serial numbers intermingle. All R aircraft had an enlarged (or additional?) oil tank in the fuselage over and above the two 300 litre drop tanks so they carried extra fuel and oil. They also had a dinghy and survival equipment etc.

The main rack capacity was changed between the B-1 and B-2 from 500 kg (500 XI B rack) to 1000 or 500 kg (1000/500 XI B rack). A similar capacity existed between the R-1 & R-2. Although the carriage of a 1000 kg bomb in anger was rare, photographs exist of both R-2 and B-2 with such weapons in use. Also remember the bomb load was potentially reduced anyway as the addition of external fuel removed the ability to load the wing bomb racks. In some cases the early R’s appear to have sacrificed any wing bomb capacity by having what look like “rackless” or “half-rack” installations with simple struts. In the main however, most R’s photographed appear to have had fitments which linked to basic 50 kg racks, suggesting they could convert and operate like normal B’s where range was unimportant. In essence, at short ranges, there was no deterioration in bomb load capacity on the centreline rack

The R-1 (like the B-1) used the Ju211A engine
The R-2 (like the B-2) used the Ju211D engine
Others:-
R-2/trop – Ju211D engine and enlarged sand filter
R-3 - Ju211D engine but fitted for glider tow and having radio equipment which could be linked through the tow cable.
R-4 used the Ju211J engine like the 87D and had modified inner wing structure similar to the D series to take self-seal tanks. It also probably had the /trop filter as standard.

The major trade-off on the B to R saga was in fuel load+bomb load vs range to target and return - with the airframes constantly reducing fuel load/all-up-weight. Its total of fuel load and bomb load could not exceed the gross weight limit and it had to reach the target chosen. Hence if you wanted max range you had to reduce the bomb load. This and the target would dictate the bomb load on any mission.

R speed was 320 km/h compared to 340 km/h for the B
R climb to height was 16 min compared to 7 min for the B
R average range was 1210 km compared to 850 km for the B (could be improved by leaving out armour) but in order to use this range you had no underwing bombs and probably only a 250 kg centreline load.

If we look at weights based upon Junkers own figures, which are also not directly comparable because of variations in armour plate etc:-

Basic Weight B-1 2750 kg, R-2 3450 kg
Gross Weight B-1 4300 kg, R-2 5600 kg
(The B-2 had trial tests up to 5500 kg gross)

The B had 480 litres of internal fuel in two 240 litre tanks. The R added to this with two external 300 litre tanks only. The R-4 had the D inner wing structure so as to use its self seal tank design but still only had 480 litres internally and 600 externally. There is some confusion in early writings about internal tankage which confuses the R tankage with that of the D series. This type (D) had the same inner wing tanks but also an auxiliary 150 litres in each outer wing (480 + 300 internally) and usually the capacity to take a 300 litre tank under each outer wing also – hence a “long range” version of the D, for example, was inappropriate.

For your information – noting the replies about fuel weight - the Luftwaffe staff RLM GL/C B2 at the time used a fuel weight conversion of 0.74 kg/litre for their data charts – this is taken from a GL/C B2, Bf110 equipment and range datasheet. I have not ever seen a similar datasheet for the Ju87 B or R but one would certainly have existed.

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Ju87R Sources - Les Whitehouse 14 Feb 2002
Best published source is the Ju87 Stuka by Griehl – German edition by Motorbuch Verlag 1998, English Edition by Airlife 2001 ISBN 1 84037 198 6.

RLM Development Bureau Programme C listed all planned R production at Weser Aircraft.

B-1’s by Weser were planned 1937 through to March 1940 and B-2 production was to cover from July to October 1940. In parallel from June 1940, Weser were also tasked with the R-1 (presumably because they could then use the existing B-1 tooling with additions for the R-1?) and were tasked with delivering these July to October 1940 as well. R-2 production was intended to follow on from the R-1 once B-2 production was completed. In reality by that time not only had all the R-1’s been completed but a further qty of 123 R-2’s had been completed in advance of the original programme - presumably because the various sites used by Weser, including the opening of Berlin-Templehof allowed an expansion of throughput on the Ju87 B and R.

Note: there is photographic evidence of R-1 in service as early as April 1940 even in Greihl’s book (captioned as an R-2) and the first operational R-1’s were used in Norway – so Weser production appears to have been in advance of formal order documents and planned programmes

Rest of the data has come from my own research on serial numbers etc., but everything I have said is collaborated in Griehl’s account. Although, to be honest, it is not laid out as clearly and tankage in particular has to be pieced together from separate sections to get and overall picture of the changes. It is also not in his usual style and does not have production or loss lists like his He177 book. Griehl actually states a 1941 publication date for the Rechlin produced data table for the R-2 but does not publish the table. Griehl also confirms that, because of the engine type and component standards, the R-1 was “in effect” a long range B-1 and the R-2 a long range B-2, but as the R-1 came in during the latter half of B-1 production it had (as did the late B-1) the later style full exhaust stacks.

One other publication I could refer you to is the booklet “Stuka – Ju87” by Richard P.Bateson, Ducimus Books, 1972. However, not only would it be difficult to find a copy, it is simply a good historical account with lots of photographs. It has little on the technical side once past the prototypes, so would probably be a waste of effort. In this one the modified fuel system (R-4) is reported only as a modified "lubrication" system.

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Range - Les Whitehouse 15 Feb 2002
Range figures can be confusing. Some records/writers will quote a figure which is an actual “radius of action” - Allowing the machine to reach its target and return. Others will quote a straight line range, presumably on the basis that the aircraft will land at its destination. In most cases the data is incomplete unless all of the conditions are known. Ie: the weight (including crew, ammo, fuel and bombs), height and speed flown (hence rate of fuel usage). Unless all of this information is considered then calculations will be inaccurate and at best a prediction.

For your information:

There were formulae developed pre war for design approximations which allow both a crude prediction (UK - spot air range) and a more accurate prediction of range (UK – optimum performance range) to be made based upon the type of airframe (its drag efficiency), fuel consumption, airscrew efficiency and ratio of airframe and disposable load. I have had good correlation between these formulae and RLM documents applying the formulae to situations with the Bf110 (such as the flight by Hess). However the application is not easy and uses a lot of approximation (that’s technical for guessing!). At Boulton Paul the problem of a consistent basis of performance prediction and comparison with other manufacturers was so frustrating that they introduced a term in their proposals known as “reinforcing range”. This was the clear “non-radius of action” situation where extra tanks were fitted and the aircraft was simply to fly a basic route and land away from base – ie: reinforce a distant base.

Fortunately, in this case, we are concerned with data which has already been obtained from technical sources and a simple sum will clarify the loading conditions of the R Airframe.

Loads:

The following range figures were reported by Bateson in the Ducimus Publication but because they are in English figures it is not known if they are the result of tests on captured aircraft or taken from German documents. I have converted back to the SI system. They look to me like typical Rechlin/RLM style altitudes and the speeds are typical of optimum cruising speeds at the time for what were termed clean, low-drag monoplane airframes like the 109/110/87 etc. so I think they have come from “official” RLM sources. This is further backed up by the presentation style of two maximum weights:-

R-1 1429 km at 270 km/h outbound, 324 km/h inbound at 5000 m altitude

R-2 1254 km at 290 km/h outbound, 330 km/h inbound at 4000 m altitude

The speed difference inbound and outbound suggests a “chosen” load for the tests but that load is not specified.

The max weight limit of the R-2 was stated as 4700 kg stressed to H5 (full aerobatics) and 5650 kg stressed to H3.

Using these and Junkers “empty” limit for the R-2, I have calculated weight in Kg, based on Air Ministry style summation, assuming all disposable load plus weapons and radio are added to the empty weight:-
Basic 3450
Crew 180
Radio 160
Oil 45
Maps etc 2
3xMG17 38
1500 rounds 90
Fuel 799
Total 4764

250 kg bomb +250
Total 5014

This suggests to me that the airframe is overloaded by more than 300 Kg on take-off for the full H5 stressing. It would have had to use up at least 2/5ths of its fuel before it could dive bomb a target.

500 kg +500
Total 5264

This suggests ok for H3 stressing but the aircraft would have to be down to 4700 Kg before it could actually dive bomb a target (over 2/3rds of its fuel load). This would be unrealistic at maximum range as it could not return to base.

[Juha]

Hello Leon
Peter C. Smith in his Junkers Ju 87 Stuka also gave the same B-1/R-1 and B-2/R-2 connection and IIRC that was also mentioned in Oct 84 AI article, but according to Smith already R-1 had two additional 150 litres wing tanks.

And Ju 87 needed less than ½ fuel to return after bombing, no external (draggy) load to carry and being much lighter during the climb back to optimum cruise height than after take off.

On ability to dive bomb, Ju 87 was already released its bomb before pull out ie before max stress to its structure.

Juha

[Birgir Thorisson]

Leon Venter:

Thank you, very informative.

Question: If each droptank fully loaded weighed about 240 kg, that is more than the bombload carried by the B on the wing racks. It is hardly compatible with extra internal tanks, as reported for R-1 in AI. But:

Basic Weight B-1 2750 kg, R-2 3450 kg
Gross Weight B-1 4300 kg, R-2 5600 kg
(The B-2 had trial tests up to 5500 kg gross)

If the empty weight of the R-2 is 700 kg. more than B1, the structure must be heavily reinforced. (The more appropriate comparison would have been with the B-2)

Birgir Thorisson

PS,
I am experiencing the disappearance of posts. E.g. the post #3 above is just a part of what I posted yesterday, which I actually saw in the full form when looking at the thread on my computer screen. Does anyone have similar experiences?
(I edited the piece twice, because I find it uncomfortable to read through my posts in the miniscule window offered by the "quick reply" option.)
Also, on the Polikarpov thread I started, two very long pieces disappeared when I tried to use the quote option to move paragraphs from previous posts into my reply. Apparently I was not doing something right there.
Is it possible in some way to go back and recover what was written in these windows, if one has lost it by some accident, before it got posted?

Edited.
PPS. when I posted this comment, the computer returned the message that it was a duplicate of a message I had posted few minutes before. Something is wrong.

Birgir

[Csaba B. Stenge]

Originally Posted by Nick Beale

Just a thought but what about the crutch that swung the bomb outside the airscrew arc when dive-bombing? Might not the strength of that be a limitation?

Good point. There were problems with that device (the normal, not strenghtened one was damaged many times by 500 kg bombs) Perhaps the Bertas used mostly 250 kg bombs on that sortie (I guess, so numerous 500 kg hits would be fatal despite of the armoured deck)