PDU Blenheims 1939/40

[leyreynolds]

Does anyone have details/photos showing camo'/markings please?

[ben_m]

Does anyone have details/photos showing camo'/markings please?

In my opinion, there were two types of Blenheim used by the PDU, those that ferried film, men and equipment to and from France- I have some photos of these and they seem to be in 'normal' camouflage for the time- dark earth and dark green over black. This role was taken shared with, then taken over by Hudsons (I also believe there were different Hudsons for logistics and for PR).

(scans from Dave Lefurgey, from Bob Niven's photo album)

Then there were those actually used for PR, of which I have never seen a photo, but I would be very interested in one!

The only evidence for the markings are the description by Sidney Cotton (quoted by Constance Babbington-Smith in 'Evidence in Camera' , and told to Ralph Barker in 'Aviator Extraordinary'), and a drawing submitted to the Air Ministry after the friendly-fire incident with Hudson N7334, which was kindly copied by Edgar from the original at Kew:

I've not got time now, but I'll copy the description by Cotton's of the modifications to the PR Mk.IVs, and I'll write about L1348, a Mk.I later today.

[Andy Fletcher]

In my opinion, there were two types of Blenheim used by the PDU, those that ferried film, men and equipment to and from France- I have some photos of these and they seem to be in 'normal' camouflage for the time- dark earth and dark green over black. This role was taken shared with, then taken over by Hudsons (I also believe there were different Hudsons for logistics and for PR).

Then there were those actually used for PR, of which I have never seen a photo, but I would be very interested in one!

Hi Ben,

I can find no evidence that Blenheims of the PDU were used for operational photo recce sorties during 39/40, only for ferry duties etc as you say. First confirmed operational use of Blenheim by PRU that I can find was in Jan 41. I have no idea what camouflage scheme was used but like the Hudson sortie profiles before, the Blenheim sorties were flown at medium to low level with sufficient cloud cover for concealment.

Best Regards

Andy Fletcher

[Edgar]

In a 1970 book, written by Peter Moss, on the Spitfire, he says that the Blenheims were Mk. IVF, which were converted at Farnborough; this consisted of removing all paint, filling cracks and holes, then painting in a semi-gloss paint. Spinners were fitted, plus tear-drop side windows, a retractable tailwheel, and Perspex front panels. Others followed, with the Heston Flight eventually getting eight airframes, all painted in Camotint. The Heston Flight was known as No.2 Camouflage Unit, from October 1939, with a "Special Survey Flight" moving to Seclin, near Lille, 5-11-39. It was not called the P.D.U. until April 1940.

Edgar

[Test Graham]

The one(s) shown in the photos do not have spinners, so may well be the unit "hacks" mentioned rather than operational aircraft: apart from the colour scheme, of course. The comment about being Mk.IVFs is a little odd, as the majority of the fighters in 1939 were Mk.Is. There would seem to be no good reason for getting fighters - all the more work involved in de-roling them - unless they were readily available, which seems unlikely at this date. Can anyone comment on operational dates for the Mk.IVF? Possibly linked to the formation of the Coastal units?

[ben_m]

Hi Ben,

I can find no evidence that Blenheims of the PDU were used for operational photo recce sorties during 39/40, only for ferry duties etc as you say. First confirmed operational use of Blenheim by PRU that I can find was in Jan 41. I have no idea what camouflage scheme was used but like the Hudson sortie profiles before, the Blenheim sorties were flown at medium to low level with sufficient cloud cover for concealment.

Best Regards

Andy Fletcher

Hi Andy,

That's interesting: it fits with Cotton's rejection of the aircraft, and also with the value he put on his crew's lives. The fact that the PDU submitted the drawing of the all-over camotint Mk.IV suggests that the aircraft were/was still flying, if not operationally.

In a 1970 book, written by Peter Moss, on the Spitfire, he says that the Blenheims were Mk. IVF, which were converted at Farnborough; this consisted of removing all paint, filling cracks and holes, then painting in a semi-gloss paint. Spinners were fitted, plus tear-drop side windows, a retractable tailwheel, and Perspex front panels. Others followed, with the Heston Flight eventually getting eight airframes, all painted in Camotint. The Heston Flight was known as No.2 Camouflage Unit, from October 1939, with a "Special Survey Flight" moving to Seclin, near Lille, 5-11-39. It was not called the P.D.U. until April 1940.

Edgar

I think there is some confusion here: I think January 1940 is the official date for foundation of the PDU. The 8 Blenheim Mk.IVF were not issued to the PDU, but were converted at Heston (probably by Heston Aircraft) under the instruction of the PDU, for fighter command. I believe after the first PR conversion(s), Cotton had proved they were unsuitable for PR, and no more conversions for PR were carried out. They probably had one or two more Mk.IVs for logistics, and one is see above- nick-named 'Joe'. G-AGAR, a Hudson disguised as a Lockheed 14, was nicknamed Cloudy Joe.

Here is the story as told by Sidney Cotton himself:

Three days after my meeting with Tedder, on 21st September, two Mark IV long-nosed Blenheims arrived at Heston. I flew one down to Farnborough and met the Chief Superintendent, Mr A.H. Hall, who showed great interest in my ideas about streamlining and polishing to increase speed. I found over the next few months that Hall was always ready to tryout new ideas, carrying out the most exhaustive calculations and tests to prove or disprove their soundness. We didn’t always agree, but it was refreshing to meet a man so lacking in prejudice.

In cleaning up the Blenheim to get more speed we had all the thick dope taken off and replaced by a hard, semi-glossy dope with a very smooth surface. All holes were blocked up and all projections smoothed or streamlined, and we fitted a spinner to the propeller which helped to cool the engines and made it unnecessary to open the gills. Teardrop windows and Perspex front panels improved vision, and a retractable tail-wheel and retracting dump valves under the petrol tank gave further streamlining. The result was a speed increase of 18 m.p.h. This was a useful increase, but it did not make the Blenheim suitable for a photographic role. We needed at least another 100 miles an hour. The Blenheim was thus a disappointment, but it served its purpose as a flying laboratory, and we imagined that we had no choice anyway but to make the best of it. As it happened, however, the streamlined Blenheim was instrumental, in a most unexpected way, in my getting hold of the Spitfires I coveted.

Air Chief Marshal Sir Hugh Dowding, C.-in-C. Fighter Command, was fitting out Blenheims as long-range fighters, although they were really much too slow for this role. The rumour soon got about that I had done something to a Blenheim to increase its speed, and Dowding turned up at Heston one day and asked me if I could really make the Blenheim go faster. We arranged that one of his pilots should test a Blenheim and note its performance and then bring it over to Heston. After we had cleaned it up the pilot said it was fully 20 m.p.h. faster. Dowding was delighted, and he appealed to the Air Ministry to ‘Cottonize’ all his Blenheims, as he called my process. The Air Ministry were sceptical about any real increase in speed, and they told Dowding that in any case they had no facilities available for carrying out such a task, so Dowding came back to me. I told him that if he would requisition another hangar for me at Heston I would do the job. We ‘Cottonized’ eight Blenheims in a week, and in addition to the speeding-up process we fitted my patent tear-drop windows which enabled the pilot to see downwards and to the rear. We painted the Blenheims the same pale green as my Lockheed, and this later became standard camouflage for all R.A.F. fighter aircraft.

Some days later Dowding invited me to tea at Stanmore. He told me how pleased he was with the Blenheims, and he asked if there was anything he could do for me, so I decided to take the plunge. ‘There is one thing, sir,’ I said, fully realizing what I was asking and fully expecting a shocked refusal. ‘Could you lend me a couple of Spitfires?’

Dowding’s face remained for the moment inscrutable. ‘What for?’

I expounded my views on the requirements of photographic reconnaissance, and Dowding listened politely enough—even perhaps attentively, I could not tell which. There was a pause when I had finished, and then Dowding spoke.

‘When would you like them?’

‘Yesterday!’

‘Would nine o’clock tomorrow morning do?’

The serials of the first two Blenheims were P4899 and P4901. In the description above, the Blenheim being converted is referred to in the singular- this is backed-up by Niven's contemporary description of visiting Farnborough to check on the progress of the conversion of 'the Blenheim'- so maybe there only ever was one conversion to PR in all-over camotint- maybe Joe was the other?

I recently discovered a photograph of a Blenheim at Heston in the background of a photo of the Heston J.5 (Nuffield Napier Heston Racer)- possibly around Feb. 1940:

I think this is an unconverted Mk.IV, possibly Joe.

Again, I've run out of time, but I will add the information I have about another Blenheim, L1348, when I have a chance.

[gingerbob]

A bit of embellishment from various sources at the PRO:

Heston Flight 19/9/39 Report to Peck

to Harrogate yesterday as arranged and saw AVM Tedder and Mr Farren. We discussed whole project.

It appears only plane available considered sufficiently out of teething troubles is Mark IV Blenheim. 100 mph slower than what is required but in order to produce results ASAP, there is no choice but to use it to start with...

two Blenheim IV being delivered Farnborough this week. Letter written to MR Hall.

(This document also already mentions interest in the Spitfire if extra fuel can be fitted, or if not then Hurricane.)

~~~~~~

Machines for Special Heston Flight 26/9/39 (report to Peck)

2 Blenheim delivered Farnborough Thursday last week and immediately work was started on one of them.

~~~~~~

"Cotton's Account"

Unit concentrated first on cleaning up Blenheim. In October proved additional 25 mph could be obtained:

i) Rub down machine, smooth finish, then re-doping

ii) block up cracks which cause turbulence

iii) Fit spinner to prop, which helped cool engine and eliminated need to open gills.

iv) Teardrop windows (made by triplex) and Perspex front panels, to improve visiblitiy

v) retract tailwheel

vi) Retract dump valves under petrol tank

vii) Eliminate fairing in front of undercarriage and fit doors parallel with underside of engine housing.

An additional 18 mph can be obtained without v, vi, vii.

~~~~~~~~~

1/3/40 "In attempting to regularise PDU establishing"

4 Hudson, 1 Spit, 1 Blenheim, 1 Harvard, 1 Lockheed (not counting 212 Sqn, with 6 (plus 2 Immediate Reserve) Spit).

In addition private aircraft used by courtesy Cotton: 1 Beechcraft [staggerwing], 1 Lockheed.

[There follows some discussion, which seems to concern only Spit and Hudson as currently operational types. The "friendly fire" loss of a Hudson was on 3 March.]

The ORB (AIR 29/413) says:

1/4/40 PDU converted to Operational unit from this date

establishment 2 Blenheim, 3 Hudson, 2 Spitfire. a/c strength: 1 Blenheim, 4 Hudson, 9 Spitfire, 1 Harvard

12/4 changed to: 4 Spit, 1 Blenheim [My notes aren't clear, but I think the other types remain unchanged. Elsewhere it says 4 Spit plus 4 Immediate Reserve, not counting the two flights in France.]

I have vague evidence in my notes that Feb '41 is the first operational use of Blenheim, which roughly agrees with Andy.

bob

[Seahawk]

Be it noted in passing that these notes record Cotton's own words that streamlining the Blenheim resulted in a speed gain of just 18 mph. I seem to recall a thread here which reported the fanciful figure of 80 mph, which ISTR we discounted then as a probable garble.

[Andy Fletcher]

As Ben says P4899 and P4901 were definitely the first two Blenheims with the PDU (Heston Flt, No.2 Camouflage Unit, et al.). Both feature extensively in Longbottom's and Niven's logbooks, but only for non-operational flights. P4901 was first flown by Niven on 25 Sep 39 and P4899 first flown, again by Niven, on 23 Oct 39.

Andy Fletcher

[sloegin57]

Again, I've run out of time, but I will add the information I have about another Blenheim, L1348, when I have a chance.

Hopefully ben_m, that will not be too long as I am following this thread with more than, for me, usual interest. All that I will add, for comment, is a scan from "Famous Bombers of the Second World War" Second Series by William Green circa 1960, of the afore mentioned Blenheim I L1348, the only photo I have ever seen of it and I'd love to know what the colours are. The underwing serial looks "different" as well.

Dennis

[Andy Fletcher]

P4901 was first flown by Niven on 25 Sep 39

This date is somewhat ambiguous. Although the date is given as 25 Sep 39, it is actually on the Oct 39 page and runs in sequence with other flights during that month, so it is probably 25 Oct 39. If this is the case the first flight of P4901 by the Heston Flt was on 08 Oct 39 with Niven as pilot.

Best Regards

Andy Fletcher

[ben_m]

Hello again, and thanks for the replies-

gingerbob- really useful information, which backs-up Cotton's later statements (Aviator Extraordinary was written in the late 60's).

sloegin57- although I already have a copy of that photo, the mention of camera blisters was new to me, but checking on the other photos I have, I think I can make two small blisters out- great extra details for when I build this aircraft.

I discovered L1348 by chance, and have for quite a while been pondering its story. Some sources suggest that it was the Cottonised Blenheim. However, some things didn't add up- Cotton's detailed explanation of the fitting of spinners, and the absence of teardrop windows (Cotton would not have left them off). The most respected source of this theory is Graham Warner's 'The Bristol Blenheim- the Complete Story':

This activity by the Blenheim squadrons took place before Cotton's small dedicated Photographic Reconnaissance Unit at Heston, named No. 2 Camouflage Fight (then Unit), became fully operational and later greatly expanded. The unit had two Blenhiems, and Cotton had one 'cleaned up' to improve its performance, he designated it PR-1, thus negating the change of unit name! This Blenheim was L1348, a Mk I on loan from 139 Squadron, and some 250 man-hours of work at Heston and Farnborough were spent in rubbing the aircraft down, sealing all the joints and gaps with tape, and repainting it with a smoother

*missing from Google Books*

with alloy, removing the turret and other armament, and replacing the standard rounded wing-tips with shorter, squarer fairings.

However, all this work produced only a slight increase in maximum speed from 263 to 278mph. Another useful modification to this aircraft was the fitting of streamlined Perspex blisters to the main side windows, which greatly improved the field of view rearwards and downwards for Pilot and Oberver; these blisters were soon being fitted to squadron aircraft. L1348 then went to Steaverton and had Rotol constant-speed propellers fitted; these and further modifications by the A&AEE at Boscombe Down produced a top speed of 294mph (true) at 13,000 feet using the take-off power settings of 2,750rpm and +9lb boost, making it the fastest Blenheim ever. But overall performance still proved inadequate for unescorted reconnaissance, and the PR-1 version was not preceded with. Cotton was still pressing hard for Spitfires, which he knew were far more suitable, and treading on many Air Ministry toes in the process.

Incidentally, L1348 saw the first use of the 'sky' colour, known colloquially as 'duck-egg blue', from Titanine's smooth Camotint range, which was developed with Cotton's help. It was soon to be used on the under-surfaces of UK-based Blenheims in place of the all-black or half-black/half-white under-surfaces then in use. These 'sky' undersides were also adopted later for other day bombers and all the other aircraft (apart from night-fighters of Fighter and Coastal Commands.

Dowding had heard of these 'high-speed' modifications, and being most anxious to improve the inadequate performance of the Mk.1-Fs in his Command, went to Heston to inspect L1348, was impressed and ordered eight more to be similarly modified. (I am unable to trace any further information on whether this was done or not.) The enterprising Cotton used this occasion to extract from Dowding two of the very scarce Spitfires, which he modified for PR work, stripping out the armament, fitting camera, and providing them with a warm-air supply to prevent condensation; their far higher speed attained at a much greater altitude made them vastly more effecting than the Blenheim for this role.

If anyone has the book, and can fill in the blank, I'd appreciate it.

In Warner's version of events, the teardrops should have been fitted before the Rotol props, but the photos taken at Staverton just after they were fitted proves this not to be the case.

The other view that I have heard is that this Mk.I was modified by A&AEE at the same time as Cotton was working on his Mk.IV(s)- an attempt to out-do the foreigner who was upsetting the status quo. A key piece of evidence to support this theory is that after the trials as 'PR-1', L1348 underwent a number of transformations, with gun belly packs, different turrets, etc.- it was definitely a A&AEE testbed aircraft. The only thing against the theory, is why choose Cotton's camotint for the undersides?

I'm not sure the definitive answer will ever be found, but I have uncovered more photos of L1348:

This is the back of the front-view photograph print, which puts L1348 at Staverton in Sept 1939. I have also seen stated that these photos came from a press-photo session in November 1939- but that doesn't make sense with the 'Secret' labeling of this print.

Things to note from the photos:

• venturi tube is covered with what appears to be gloss-dope-covered fabric.

• metal nose panels

• clipped wings- "3ft shorter wing span"

• dark gloss dope on leading edges and wing roots

• lighter-filler? on trailing edge root

• Rotol constant-speed props

• can just make out the two camera bumps in the front view

• photos taken on ortho film- yellow of roundel is very dark

• I believed the colours to be dark earth and dark green over sky.

Having just though about the underside colour, it doesn't look quite right for freshly painted sky- could it be that the camotint/sky link was a red-herring, due to the confusion over this and the Cottonised Mk.IVs? Could the undersides be aluminium painted? I had assumed the colour, as every time this plane is mentioned, so is camotint/sky. I don't see why they would re-paint the large pre-war style serials under the wings if they had just painted the undersides in camotint/sky.

Any thoughts very welcome!

[leyreynolds]

Thanks for all the above. It's obviously a far more complicated story than I had imagined. In any event L1348 looks like an interesting project!

[occa]

At least we at last now have a photo of a Blenheim with a removed turret ...

Re the underside color, couldn't it be they pained around the serials?

And what about the uppersides being EDSG/DSG?

I am just thinking out loud here, I have no evidence in this direction.

Edited July 22, 2012 by occa

[Mike S]

Thanks for all the above. It's obviously a far more complicated story than I had imagined. In any event L1348 looks like an interesting project!

Having just come in on this interesting thread, I noticed other features on the photographs not yet mentioned. The colour demarcation lines are uneven and rough along the wings, lower fuselage and engine cowling. This strongly suggests to me an undersurface repaint. The serial is still visible on the rudder which suggests no change in the upper surface colours; ESG /DSG were not a scheme in 1939. The dark area under the leading edge might be black, it is difficult to be sure with the reflections off adjacent the top surface.

[Andy Fletcher]

The other view that I have heard is that this Mk.I was modified by A&AEE at the same time as Cotton was working on his Mk.IV(s)- an attempt to out-do the foreigner who was upsetting the status quo. A key piece of evidence to support this theory is that after the trials as 'PR-1', L1348 underwent a number of transformations, with gun belly packs, different turrets, etc.- it was definitely a A&AEE testbed aircraft. The only thing against the theory, is why choose Cotton's camotint for the undersides?

Any thoughts very welcome!

Hi Ben,

If L1348 was ever with the Heston Flt (No.2 CU et al.) it wasn't ever flown by Niven or Longbottom, at least never recorded in their logbooks. Considering they were Cotton's main men in the early days, with Longbottom in particular being responsible for most of the flight testing, it would support what you say about L1348 being modified by A&AEE.

Best Regards

Andy Fletcher

[ben_m]

Having just come in on this interesting thread, I noticed other features on the photographs not yet mentioned. The colour demarcation lines are uneven and rough along the wings, lower fuselage and engine cowling. This strongly suggests to me an undersurface repaint. The serial is still visible on the rudder which suggests no change in the upper surface colours; ESG /DSG were not a scheme in 1939. The dark area under the leading edge might be black, it is difficult to be sure with the reflections off adjacent the top surface.

Hi Mike, thanks for your input. I have seen wavy underside margins on Blenheim Mk.Is, e.g. on this photo, under the fuselage roundel, and the high start to the black on the cowlings.

On a higher resolution version of the first photo of L1348 I posted, it is clear to me that the dark strip under wing leading edge is continuous with the upper gloss strip along the leading edge. In fact this, and the other areas of dark glossy doped fabric (e.g. over the new wingtips, wing roots, the nacelle to wing joints) suggest to me it hasn't been repainted on the underside- if you were painting an aircraft in a new smoother paint, you would do it after all the filling/smoothing jobs were done, not before.

I have convinced myself that at the time of these photos, L1348 had aluminium painted undersides. It could well still have been the first aircraft to trial sky under-surfaces (after these photos), and maybe, as Graham Warner states, had teardrop blisters added on the windows. But likely these additions were after seeing Cotton's version of a 'speed Blenheim', which was able to obtain almost the same performance without removing the turret, wing tips or tuning the engine. It might have been this comparison that brought home the importance of the smooth paint.

Now, is there a markings expert who can tell us whether the upper roundels would be A1 or B type?

At the moment, I am leaning towards A1 roundels on upper wings.

Edited July 23, 2012 by ben_m

[Nick Millman]

FWIW the under surfaces look to me like aluminium rather than Sky and I'm leaning more towards unpainted than painted although that's a tough call.

[Test Graham]

EDSG/DSG was indeed already a scheme in 1939, certainly well before December, within the FAA and on Coastal's Sunderlands. However, the dark tones on this photo rather cast doubt on this scheme.

[ben_m]

After many years of hoping one existed, I have located a photo of an all-over Sky Blenheim! And it was at the IWM- I'm not sure how long ago it was scanned, but today is the first time I have seen it.

From IWM, used under Fair Use for the purposes of discussion and education.

I believe this modification was the +18 mph version, as described in Cotton's description of the mods, i.e. without retractable dump valves under fuel tank, without doors for tailwheel retract, and without new main gear doors.

Really good timing for this to turn up this year, with the Airfix kit on the horizon.

[Test Graham]

Excellent photo, and a superb thread. However, is it true that Cotton didn't remove the turret? It would seem to be the most obvious speed gain available.

It does seem that Cotton concentrated on the simpler steps that could be taken - leaving aside the fuel dump and wheel doors which would require some rework - whereas RAE concentrated on more involved measures of a new nose and wingtips. So 294mph does not seem to be the best that could have been obtained from a combination of both routes, but this would have lengthened the time required for each conversion and presumably would still have been lower than desired.

The other step is the matter of these fighters supposedly "Cottonised". Are there photos of these aircraft with spinners and (presumably) Type S camouflage?

[gingerbob]

Just to add a relevant comment I've crossed paths with:

AIR 20/425 Monthly liaison meetings DGRD/ACAS [obviously my "quick and dirty" transcription]

4/10/39

High Speed Photographic a/c as an immediate requirement.

Discussion on possibility of adopting the following: [goes on to consider other types]

a) Blenheim: increase of 36 mph at low altitude already obtained by overboosting, and clean up. At high altitude only 4 mph due to need to throttle engine to avoid over rpm. Can be fixed with Rotol. [that is, replace 2-position prop with constant-speed]

bob

[ben_m]

Thanks Bob, very interesting, and ties in with the fitting of Rotols in September to L1348 (by 4th October maybe they hadn't been tested, or the results reached the people in the meeting).

I'm interested to know what other aircraft were considered for adoption.

[Selwyn]

After many years of hoping one existed, I have located a photo of an all-over Sky Blenheim! And it was at the IWM- I'm not sure how long ago it was scanned, but today is the first time I have seen it.

The caption states it is P4899.

From IWM, used under Fair Use for the purposes of discussion and education.

I believe this modification was the +18 mph version, as described in Cotton's description of the mods, i.e. without retractable dump valves under fuel tank, without doors for tailwheel retract, and without new main gear doors.

Really good timing for this to turn up this year, with the Airfix kit on the horizon.

The caption at the IWM says it was taken in France at Lille Seclin, which asks the question if it was used operationally?

Selwyn

[Test Graham]

Note toned-down roundels under the wings - have these been noticed elsewhere on PRU aircraft?