Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

When General Werner von Fritsch, the then commander-in-chief of the German Army, predicted in 1938 that "the military organization which has the best reconnaissance unit will win the next war," few doubted that, in aerial reconnaissance and photography, the Luftwaffe reigned supreme. This, however, proved to be far from the case.

Although the Germans began World War II with an efficient air reconnaissance and photographic interpretation system, they did not develop or improve it as the conflict widened and progressed. Though starting from far behind, the British, in contrast, were to bring about a revolution in aerial photography and air intelligence that was to play a vital part in transforming the fortunes of the war. As the RAF slowly began to gain air superiority over the increasingly hard-pressed Luftwaffe, nothing, it seemed, escaped the probing of its photographic spies in the skies.

Spitfires and Mosquitoes

Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

Choosing the right aircraft was the key to success. Where Sidney Cotton had pioneered the way, the RAF followed. The Spitfire, in its various reconnaissance versions, became the main aircraft of choice for its photo-reconnaissance squadrons. Unarmed—except for one low-flying variant, which retained its original eight machine guns—it relied on speed and altitude to ensure its survival.

Consequently, throughout the war, there was a steady increase in performance within the Spitfire reconnaissance family. The last of the wartime variants, the Spitfire XIX, could fly over 100mph (160km/h) faster, two miles (3.22km) higher, and more than four times farther than Cotton's pioneer PR 1A. However, the Spitfire XI, of which 471 were produced, was the most numerous of these magnificent aircraft. It could fly at 422mph (679.14km/h), possessed a service ceiling of 44,000ft (13,411m), and had a maximum range of more than 2,000 miles (3,220km).

As good as the Spitfire was, the twin-engine de Havilland DH 88 Mosquito was probably the best all-round photo-reconnaissance aircraft to go into service with the RAF during the entire war. The first, the PR 1, was delivered to the RAF on June 2, 1941. Seven variations were to follow. Fast, agile in the air, and lightweight thanks to its wooden airframe, the Mosquito could fly as quickly, sometimes quicker, than a Spitfire and enjoyed double the Spitfire's range. By early 1942, UK-based Mosquitoes were regularly flying reconnaissance sorties as far away as northern Norway, East Prussia, and the north of Italy.

Despite its small size, the Spitfire's fuselage was still big enough to accommodate a variety of camera configurations, while cameras could also be mounted in the wings to provide oblique photographic coverage. The mounting-point in the fuselage was just behind the centerline fuel tank. The cameras were split verticals with the largest lenses that could be fitted into the airframe. The Mosquito's fuselage was roomier and so could accommodate any required camera configuration. The commonest involved three cameras—a single short-lens area collector and two long focal length ones, mounted as split verticals for taking more detailed shots of specific objectives. Forward obliques could be taken from the nose or from wing pods to gather stereo images.

Some of the mounting points could be accessed by the aircrew—the Mosquito accommodated a navigator asmwell as a pilot—which meant that film magazines could be changed in flight. Naturally, this greatly increased the number of photographs that could be obtained.

Reconnaissance Routine

Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

When the weather was clear, reconnaissance pilots often flew several reconnaissance sorties a day—at their peak, in the run-up to D-Day in 1944, many were averaging up to eight. With up to 500 exposures on each roll of film the pilots brought back, staffing levels at RAF Medmenhamincreased exponentially. At the start, Medmenham had an establishment of 114 officers and 117 other ranks. By the end of the war, there were around 550 officers and 3,000 other ranks working there. They included many Americans.

The staff—mostly an eclectic mix of boffins and academics with quite a few women among them—comprised some of the best brains in the country. Geoffrey Stone, an army photographic interpreter posted to Medmenham prior to D-Day, recalled that the place was nothing like a "regimented military establishment." It was "much more like an academic institution full of civilians in uniform." Glyn Daniel, the first Cambridge archaeologist to be recruited to the Medmenham operation, described his new colleagues as "an ill-assembled collection of dons, artists, ballet designers, newspaper editors, and writers." There was no doubting, however, the dedication they brought to their new jobs.

Archaeologists like Daniel were prized because of their ability to piece together tiny scraps of information to produce a comprehensive intelligence picture. Dorothy Garrod, Disney Professor of Archaeology at Cambridge, joined Medmenham as a member of the Women's Auxiliary Air Force (WAAF), became a SectionOfficer and made herself Medmenham's expert on the movement of supplies and troops by train. Explorers and geologists were equally valued. Many found their peacetime experiences invaluable. Constance Babington Smith, a young WAAF officer who had been a pre-war journalist on The Aeroplane, won fame for being the first to identity one of the Third Reich's most-closely guarded secrets, the VI Flying Bomb.

Not everyone took to the life. Elizabeth Johnston- Smith, a 19-year-old WAAF who came to Medmenhamto train as a photographic interpreter, said the place had "a fuddy-duddy, middle-aged feel to it," which she did not care for at all. The hours were long, the tasks taxing, and the pressure unrelenting. Night and day every day of the year, work went on continuously. To cope with the burden, Medmenham personnel worked a shift system. For day workers, the norm was 12 hours on and then 24 hours off. Nightshift personnel worked from 8:00 p.m. to 8:00 a.m. They got 36 hours off.

Training Photographic Interpreters

Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

All prospective photographic interpreters posted to Medmenham had to undertake an introductory training course. There were no exceptions, regardless of any past experience. Douglas Kendell, who had worked with the Aircraft Operating Company before the war and then with Sidney Cotton, was put in charge of setting up the course; Pilot Officer Alfred Stevenson eventually took over from him. By the end of the war, he had trained 1,300 would-be photographic interpreters successfully.

The course lasted two weeks, during which time its participants learned the basics of the various skills a proficient photographic interpreter required. Some, like patience, attention to detail, and a good visual memory could not be taught. Successful photographic interpreters also possessed the kind of mind that enjoyed solving what often proved to be knotty problems. The starting point was learning how to identify objects on the ground as seen from high up in the air. Railways, for instance, had to be distinguished from roads as did fighter airstrips from bomber airfields. Next, the students were introduced to stereoscopic viewing. They were taught how to handle a stereoscopic viewing frame—this was universally referred to simply as a "Stereo." The two photographic prints that fitted into it were termed a "Stereo Pair."

Viewing objects on the ground in 3D made it easier to identify them. It also made it possible to measure them. The logical first step was to work out the scale of the photographs. Once this had been established, the size of every object in them could be calculated, though many found it hard to master the intricacies of working with a slide-rule. Finally, the trainee photographic interpreters were taught how to distinguish objects of military significance and especially how to seek out any telltale signs denoting untoward enemy activity.

Photographic Interpretation in Action

Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

Actual photographic interpretation involved several phases or stages. The First Phase, as it was termed, was carried out as soon as possible after the photographs had been developed and printed. The aim was to spot urgent military information. Second Phase analysis followed. This was a more elaborate process, undertaken by a large team examining the photographs in more detail. What the team detected formed the basis for the daily reports RAF Medmenham produced, summarizing every aspect of enemy activity.

The Third Phase was the key to building a greater understanding of specific aspects of the enemy war effort. It involved close photographic analysis by specific dedicated working sections. Section A dealt with enemy shipping. It had plenty of material to work with—from 1941 onward, every port in Occupied Europe was photographed at least once a week, provided the weather was favorable. One of the section's key figures was David Brachi, another of those who came to RAF Medmenham having worked for the Aircraft Operating Company. Among his achievements was his identification of a new class of German destroyer, but his real speciality was monitoring U-boat construction. By carefully charting each stage of the process, he was able to amass enough evidence to be able to deduce how many new U-boats were being built up to a year ahead. In early 1941, for instance, he predicted that U-boat production would double by the end of the year. The report went straight to the highest levels of naval intelligence, then to the chiefs of staff and finally to the War Cabinet, where it was seen by Churchill himself.

Section C studied enemy airfields, while Section E devoted itself to spotting all kinds of camouflage. Section F concentrated on railways, roads, and river and canal transport. Section L specialized in aircraft identification, while the aptly-named Section N concentrated on night photography. Other sections focused on industry, army sites, and bomber targeting and damage assessment. During the entire course of the war, none of the other belligerents managed to build up such a sophisticated air intelligence operation.

Section C, in particular, was faced with an arduous task. There were 400 Luftwaffe air bases in France and the Low Countries alone and hundreds more scattered through the Mediterranean. The photographic interpreters first set about establishing which aircraft flew from what bases. The Luftwaffe's fighters, for instance, more often than not flew from smaller bases with grass landing strips. German bombers and transport aircraft, on the other hand, usually needed longer concrete runways in order to be able to take off and land without damage.

This was by no means all Section C spent its time observing. Its photographic interpreters also kept a close watch-out for signs of airfield expansion, particularly the building of new hangars and taxiways or the extension of runways and the installation of flare paths. They had to be able to recognize existing aircraft types and spot new ones as and when they were introduced. Often, building activity was an anticipation of the arrival of new aircraft. In 1944, for instance, when the Luftwaffe started to prepare to receive its first jets, the interpreters spotted not only that runways were being lengthened but that new fuel dumps were also being built to accommodate the needs of the new aircraft. They went on from this to predict the approximate number of jets the Germans, in theory, would be able to deploy.

Only the most talented photographic interpreters were considered suitable for working on Phase Three analysis. Constance Babington Smith was one of them. As well as being the photographic interpreter who first spotted a V1 Flying Bomb on its way for testing, she was the first to spot the Messerschmitt Me 163 rocket fighter, the Heinkel He 28, the world's first jet fighter, and the revolutionary Messerschmitt Me 262, the twin-engine jet fighter that, fortunately for British and American airmen, Hitler insisted be redesigned to be deployed as a fighter-bomber. She and her team detected other top-secret German aircraft prototypes into the bargain.

Babington Smith's photographic detective work in Section L was praised by no less a person than Group Captain Frank Whittle, the inventor of the original jet engine. He visited her at RAF Medmenham where he appeared to fall for the WAAF officer. Babington Smith later discovered that he had tried to find out from her colleagues what sort of scent she was wearing. It was Guerlain'sL'HeureBleue—a classy French perfume that was hard to find in wartime Britain. Babington Smith wore it, she said, to try to counteract the masculine effect of her service uniform.

Maps and Models

Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

Map-making was another important part of RAF Medmenham's activities. The route of each photographic reconnaissance sortie and outline plots of the photographs taken on it had to be traced onto small-scale maps to create a permanent record of what had been photographed—and, more often than not, photographed again—when and where. The latter was particularly important, since the photographic interpreters needed all the photographs that could be mustered for purposes of comparison.

It was precision work, which required great skill and fine attention to detail. It was reckoned that a first class tracer could plot around 100 photographs an hour. The finished plots were cut out and mounted on a master map for future reference. The original prints were dispatched to RAF Medmenham's Photographic Library. This housed a truly mammoth photographic collection, which expanded at the rate of about a million photographs a month as the war reached its height.

The long rolls of negative film shot by the reconnaissance Spitfires and Mosquitoes were also stored in the capacious library. New prints from them could be requested whenever they were needed. A vast Williamson Multiprinter from Kodak speeded up the process. Working flat out, it could print up to 1,000 photographs an hour. The librarians—there were 275 of them—boasted that they could find or produce prints of photographs taken almost anywhere over Europe in a matter of minutes. By 1944, they were producing up to 140,000 duplicate photographs a month and, by the end of the war, they were storing approximately seven million photographic prints from all the main fighting fronts.

Section V was responsible for model-making. Initially, the section was based in the basement of DanesfieldHouse, which was converted into a carpenter's workshop, but it soon spread to outbuildings scattered through the grounds. Geoffrey Deeley, a successful sculptor, was the chief model-maker. Others included Alan Sorell, a well-known artist, and Leslie Durbin, a celebrated silversmith.

The section used the aerial photographs that werepassed across to them as reference for the three dimensional models they spent their time lovingly creating. Initially, they started by making individual models of ships, aircraft, tanks and other military vehicles, military installations, other buildings, and even railway locomotives and goods wagons. New photographic interpreters used them as recognition guides. Soon, however, the model-makers grew more ambitious. They began creating models of entire landscapes that could be as much as 20 sq. ft (1.85m²). Cliffs, beaches, ports, harbors, dams, and specific groups of buildings, such as radar stations, were all produced in full detail precisely to scale. They were triumphs of the model-makers' art.

Building the Models

Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

Each model was constructed as follows. First, the model-makers built up an accurate representation of the overall terrain by layer on layer of hardboard cut-outs on a baseboard. They used maps as extra reference to back up their photographs. Then they covered the layered cutouts with rubber or plastic to create a more realistic effect.

The next step was even more complicated. It involved creating a mosaic of vertical aerial photographs over the model. This was a skillful job, as it usually meant cutting out several photographs to give the model what might be termed a photographic "skin." This was painted to simulate the look of a real landscape, complete with rivers, roads, fields, woods, and trees. Finally, individual models of key installations or buildings were made separately and then placed carefully in position. During every stage of the process, Third Phase specialists checked and double-checked the model-makers' work to ensure that what was being produced was as accurate as possible.

By the time the war ended, Medmenham'smodelmakershad churned out more than 1,400 models. Some, like the models of the Möhne, Eder, and Sorpedams used to brief the Dam Busters prior to their famous 1943 air attack, were extremely elaborate. Such was the reliance Bomber Command placed on them that, according to Paul Brickhill, author of TheDam Busters, the aircrews taking part in the attack were instructed to "look at these until your eyes stick out and you've got every detail photographed on your mind. Then go away and draw them from memory, come back and check your drawings, correct them, then go away and draw them again till you're perfect."

Sometimes, too, the models were photographed lit in a way that replicated exactly what the location must look like on a moonlit night. The biggest task Section V undertook involved building 97 separate models of the Normandy beaches as part of the preparations for the June 1944 D-Day landings. In order to produce the many copies of the models the Overlord planners required, the model-makers made plastic molds from the originals in order to produce the required number of duplicates.

Spotting Decoys

As the RAF's bombing offensive slowly built up its strength, the Germans tried to divert the bombers away from their targets by setting up hundreds of decoy sites. There was nothing new in this; the British had done much the same thing when they implemented Operation Starfish to try to fool the Luftwaffe during the Blitz. The German plan worked for a time, until Geoffrey Dimbleby began studying the countryside around priority RAF targets in the Ruhr Valley and along the Rhine. He spotted hundreds of craters in fields where, by triggering decoy fires, the Germans had tricked the bombers into dropping their bomb-loads.

It was an easy enough mistake to make. Many Bomber Command aircrews were already bombing on estimated time of arrival over their targets and their accuracy was substantially inaccurate as a result. Seen from 20,000ft (6,100m) or so, the fires the Germans set could easily be mistaken for burning buildings. Dimbleby was put in charge of a new section—Q Section—at RAF Medmenham with orders to solve the problem the various decoy sites were posing. They got to work and, around Cologne alone, quickly identified 17 different decoy sites.

The Germans even attempted the Herculean taskof trying to camouflage their capital. The surface ofthe East-West Axis, the city's most important distinguishing landmark, was sprayed with dark green paint to blend in with the surrounding Tiergarten.An overhead cover of wire matting, interwoven with green material to resemble vegetation, was also strung over it for a considerable distance. In Hamburg, the main railway station had a false roof built over it in the shape of a small hill. The photographic interpreters, though, found such efforts relatively easy to spot in photographs, as opposed to with the naked eye from the air, because the camouflaged areas looked visually different to the actual landscape surrounding them. Comparing photographic coverage shots could also be a dead giveaway. E Section, headed by WAAF officer Molly "Tommy" Thompson, briefed photographic interpreters on what to look out for and how to spot it.

Dummy airfields featured prominently in the German decoy scheme. They were often sited close to actual airfields and populated with dummy airplanes in the hopes that attacking aircraft would be fooled into bombing and strafing them. The dummies were often so realistic that even experienced photographic interpreters sometimes found it difficult to distinguish them from the real thing. Oil depots and storage tanks were shrouded with camouflage netting to look like fields. The Germans used smokescreens as well—both to try to conceal actual targets and as decoys. Despite their efforts, the majority of the bombers got through.


Spies in the Skies: How Aerial Surveillance Tipped the Balance of WWII

World War II From Above: An Aerial View of the Global Conflict by Jeremy Harwood is available from Amazon.