The aircraft of World War I were constructed from wood frame and had high quality linen stretched over it. To seal and protect this linen from the elements it was 'doped' with a cellulitic covering. The dopings used by the British in World War I were commonly known as PC10, PC12 and CDL. Where the PC is believed to have stood for protective coating, and CDL stands for clear doped linen. These were applied over the linen cloth of the wings, fuselage and tail of the aircraft.

The Australian Flying Corps [AFC] aircraft were all from British stock and factories. Consequently the dopings for the AFC aircraft were the same as the Royal Air Force [RAF], Royal Flying Corps [RFC] and Royal Naval Air Service [RNAS]. These dopings were commonly PC10 on the upper surfaces and CDL under the wings and elevators.

PC10 is a bit of a slippery colour for historians to nail down as it changed from a brown to green shade as the war progressed. Additionally as it was subject to weathering it browned in colour.

Another issue is that quality control was not the same in 1916 as it is in modern factories that have the benefits of digital technology and statistical process control. PC10 was very definitely a bucket chemistry proposition.

Bristol Fighter of No.1 Sqn AFC in the protective covering of PC10 doping. The engine cowl is painted in battleship grey.

For one hundred gallons of PC10 the recipe is:

260 pounds nitro Cellulose syrup

74 pounds of pigments in the following proportions:

40 pounds yellow ochre
30 pounds umber
2 pounds 8 ounces Red Ochre
1 pound 8 ounces Chinese Blue

Which was then added to:

20 gallons Acetone or Methyl ethyl ketone
15 gallons Amyl Acetate
15 Gallons benzol
15 gallons Methylated spirit

As can be seen from the 'recipe' it is more like baking a cake than the precision of modern factories which produce identical products 24/7 with minimal variation.

The AFC squadrons in France were very uniform in their dopings; largely being with PC10 upper and CDL lower with either polished or grey cowls. The training squadrons in England had higher variation including red, white and black-and-white checkered aircraft.

The anomaly is No.1 Squadron AFC in the Middle East. They seemed to go through phases where aircraft were relatively uniform in dopings but outside of the standards of the AFC/RFC squadrons in France.

For instance their BE2s and BE12s appear to be uniformly CDL all over until they went through a period where PC12 - PC10s reddish cousin - started appearing on their upper surfaces. The Martinsydes in No.1 squadron went through a similar phase. One aircraft it seems was CDL lower, PC12 upper and a PC10 tailfin - complete with white serial.

Martinsyde G100 of No.1 Sqn AFC with PC12 upper surfaces and PC10 tail. Profile is taken from a photo in One Airman's War

The Martinsydes then appear to have been standardised on all-over CDL before the Bristol Fighter's made their appearance in the squadron. Initially the Bristol Fighters had a mix of white and PC10 markings.

Bristol Fighter A7194 of No.1 Sqn AFC with white and PC10 upper surfaces.

Like the Martinsyde, the Bristol Fighters became standardised in the PC10 uppers and CDL lowers, though one aircraft was recorded as being yellow all over, there has been no photographic evidence of the 'yellow peril' Biff. It may have been ochre, CDL or erroneously reported as yellow.

The Australian War Memorial collections database tantalisingly had an entry, "A Bristol Fighter which was christened by the Hun pilots 'The Yellow Peril', starting out on a reconnaissance. The billets of the 40th Wing, Australian Flying Corps, are in the background." but no photograph. The entry now has a photo of C4627: so is the Bristol yellow, yellow ochre, CDL or mis-identified?

From the AWM Collections database:

As can be quickly seen from the photograph the aircraft is in too much shadow to determine if it is yellow or not. There is also no way to confirm the aircraft's serial.

Due to the nature of orthochromatic photography that was used during that time we would expect a yellow aircraft to appear as being black. The warm colours in an orthochromatic photo darken, such as yellow and red, while the cool colours become lighter, such as blue. It would be difficult to pick if the aircraft was yellow or PC10 anyway, though it would quickly confirm if the aircraft was all over CDL or not.

As a display of this effect from the film the photo of the Belgian Nieuport below shows it dramatically. The Belgian roundel is red, yellow with a black centre. In orthochromatic film it appears as one large black disc. If C4627 was all over yellow we would expect it to appear on film as a very dark black.

Source: Nieuport Fighters by J.M. Bruce. Albatros Production, Windsock Datafile.

As can be seen from the Belgian roundel inset in the picture the orthochromatic films skews the colours. So the mystery of Paul and Weir's Yellow Peril remains without photographic evidence. Was it yellow? Yellow ochre, as Ross Moorhouse has suggested, or was it CDL (Clear doped linen)? Or has it, as Andrew Smith suggested, been incorrectly equated with the wrong serial number?

C4627 painted yellow.

C4627 painted in yellow ochre.

C4627 in CDL.

The Corps squadrons on the British front had flights attached to them with Rolls Royce engined Bristol Fighters that were intended to conduct long-range reconnaissance missions of a tactical nature. The flights were to be manned by the pilots and servicemen of the squadrons they were attached to. O Flight RAF was attached to 3 Sqn AFC.

Bristol Fighter E2529 flown by Lieutenant W. Palstra and Lieutenant E.A.D. Hamilton, O Flight RAF. 1918. Profile from photograph in Charles Schaedel's The Men and Machines of the Australian Flying Corps"

The Royal Air Force recognised the need for longer range tactical reconnaissance missions to be flown. These would be best served by the Corps squadrons which were still flying RE8 aircraft as they had in 1917. For long range reconnaissance it was decided to equip five flights with Bristol Fighter aircraft and attach them to existing Corps squadrons. It had been expected the Corps squadrons would receive Sunbeam Arab engined Bristol Fighters to replace their RE8's. However problems with the Sunbeam Arab led to the delay (3 Sqn AFC did receive a couple before the end of the war and flew them in 1919). The long range flights received Rolls Royce engined Bristol Fighters. Harry Wrigley in "The Battle Below" explains how O Flight came into being with 3 Squadron Australian Flying Corps;

It was during this period also that the organisation of a flight of Bristol Fighter aircraft, to be attached to No.3 Squadron for the purpose of carrying out long-distance work, was taken in hand. This was to be a self-contained unit composed of Royal Air Force personnel, with the exception of the pilots and observers, who were to be provided from No.3 Squadron. Captain E.J. Jones was transferred from the command of A Flight to the command of the new flight, the official designation of which was 'O' Flight, Royal Air Force.

The squadron was flying the two Bristols they received on special reconnaissances by October 23rd. Lieutenant Loftes and 2nd Lieutenant Cherry, Harry Wrigley writes of the special mission;

The route followed on this reconnaissance was along the western and northern sides of the Forest of Mormal and back along the River Sambre, and Lieutenant Loftes was instructed to pay particular attention to the important railway junction north of Leval. During the course of their flight, Lieutenant Loftes and Cherry reported several trains in the vicinity of Leval had also reported and called for artillery fire against an enemy balloon on the ground north of Maroilles, and against a six gun battery in a small clearing on the western edge of the Forest of Mormal south east of Jolimetz. In addition they reported that all the bridges over the River Sambre between Landrecies and Leval were intact, that numerous foot bridges had been constructed across that section of river that skirts the south eastern edge of the Forest of Mormal, and that the enemy aerodrome east of Aulnoye had been evacuated.

Another important special mission was carried out on October the 30th when Captain E.J. Jones and Lieutenant C.W.B. Loftes with 2nd Lieutenant A.D. Cherry and Lieutenant J.H.B.Lawson as observers searched for a special observation station in a local forest. Again Harry Wrigley provides the details;

For some time it had been suspected that the enemy had a special observation post somewhere in the Forest of Mormal, and the object of this reconnaissance was to discover it if possible. Captain Jones and Lieutenant Loftes flew in company, carefully searching the forest, and succeeded in locating a girder type tower of timber painted a dark grey and about four times the height of the trees in the forest. It was situated approximately one mile south-east of Locquignol, and was undoubtedly the observation post referred to.

The O Flight aircraft were capable of providing escort for themselves and each other. On one occasion when Lieutenant W. Palstra and Lieutenant E.A.D. Hamilton were taking photographs of the German lines facing west, this required the photographs to be taken with the Bristol deep in German airspace. The aircraft of Captain E.J. Jones flew in tandem with Palstra's providing escort cover. O Flight continued to work in strategic reconnaissance until the end of the war when the Australian Flying Corps aircrew serving with O Flight returned to 3 Squadron.

I love these photos of Bristol Fighters in the air. They are from No.1 Squadron Australian Flying Corps which flew in the Middle East through out World War I. Originally the squadron flew old and slow BE2 aircraft, before they started receiving other reconn aircraft such as the BE12, Martinsyde and RE8. None of them were particularly great as aircraft.

In late 1917 the Royal Flying Corps squadron, No.111 was formed in Egypt and had a mix of scout aircraft including the Bristol Fighter. They were transitioned to a pure scout squadron with SE5 aircraft and No.1 AFC received their Bristol Fighters.

Major Richard Williams made a pitch for them as they were having difficulty timing the No.111 escorts and the Australian reconn aircraft. Which meant the Australian aircraft were often short of fuel during a mission after waiting for their escorts.

The main value of the Bristol Fighters was that they could do both the escort and reconn role at the one time. They were the perfect aircraft for the form of aerial combat in the Middle East. They were long range, they had a pilot and an observer, they could bomb, and they could fighter the German Albatros scouts on relatively equal terms.

The Australian squadron excelled once they received the Bristol Fighters and gained air superiority quickly with them. The aircraft went through some weird color schemes. For some reason, and it is not recorded, they painted many of them white or a mix of green (PC10) and white. Eventually it seemed they standardized on the normal colors of green (PC10) with linen colored undersides (CDL). In some of the photos from late 1917 and early 1918 you will see white Bristol Fighters - like in the top photo.

A photo of Bristol Fighter B1148 from the Australian War Memorial. The photo is out of copyright. The early Bristol Fighters during 1918 were painted a mix of white and dark green. The greenish color was known as PC10 which was more of an olive green that had brownish hues or tones. It was more of a protective coat than camouflage.

It is not known why the Australian pilots painted their aircraft in whites or bands of green and white. It has been suggested so they could be spotted if their aircraft went down in the Egyptian, Palestinian and Syrian deserts. However, it appears in about mid March of 1918 they started standardizing on the PC10 upper surfaces (olive green) and CDL (clear doped linen) under-surfaces. So the colour variations pretty much exited the squadron after that date.

This is a well known color photograph taken by Frank Hurley when he was in Palestine with No.1 Squadron Australian Flying Corps. During his time there in early 1918 he took several color photographs which are very rare for the World War I period. The Bristol Fighter in the photograph is A7194 which was often flown by pilot Lieutenant Len Potts and observer Lieutenant Fred Hancock.

They scored a victory in this aircraft on the 17th of January, 1918 which they described as;

While on reconnaissance of Tulkeran, Nablus area, escorted by another Bristol Fighter at Lubban we met two formations of H.A., one of 5 which was about 500 feet below us, and the other of 3 about 1000 feet above us and about 100 yards East. All H.A. appeared to be Albatros Scouts.

The formation of 5 passed beneath our tail. I turned and dived on the last machine of formation, leaving escort machine above me to look after 3 Scouts above, who did not show any inclination to attack. I fired a burst of about 30 into H.A. who was seen to lose control of machine which turned on it's back and went down completely out of control. I turned my attention ot the other machines so could not follow down. The H.A. then broke off the engagement.

Observer fired 100 rounds at different machines of the formations

The Potts brothers were from the Hawkesbury area in Sydney. One of the brothers was shot down and killed in an engagement with a German aircraft which must have been tough for the surviving brother. It is hard to remember that the men doing the fighting were in their early twenties.

Bristol Fighter and Martinsyde G100/G102 Elephant in flight over Palestine. This was another photograph taken by Frank Hurley. The Bristol is definitely more elegant in flight than the Martinsyde.