photographic reconnaissance (PR) was, next to
signals intelligence warfare, the primary source of intelligence during the Second World War. As early as 1938 the commander-in-chief of the German Army,
General von Fritsch, stated that ‘the country with the best reconnaissance will win the next war’ and it has been said that ‘The American armed Services could not take a step and could not fire a shot without photographs and the maps that were created from them.’ ( S. Moeller,
Shooting War, New York, 1989, p. 192). In the UK PR was initially developed by Group Captain F. Winterbotham within
MI6, the British Secret Intelligence Service. In September 1938 he approached an Australian businessman, Sidney Cotton, who dealt in a new type of film. Cotton agreed to fly an aircraft fitted with cameras for his business trips to Germany and Italy. Between them they pioneered new techniques in aerial photography which were used to good effect when war came and the RAF assumed control of all PR.
In the light of Cotton's experiments the RAF was quickly forced to abandon its pre-war belief that PR could be undertaken by any competent pilot flying existing aircraft. Instead, they developed the use of fast unarmed aircraft (mainly Spitfires and Mosquitoes) to fly high-altitude sorties which avoided enemy defences. The RAF also adapted armed single-engined fighters for low-level reconnaissance in preference to the vulnerable Lysander light aircraft with which it entered the war. The RAF eventually established a separate PR group, for strategic reconnaissance, and dedicated wings for the tactical role. The tactical wings were allocated mobile processing units to provide rapid interpretation facilities on a large scale—the units of 84 Group alone produced 4.5 million prints between the Normandy landings on 6 June 1944 (see
OVERLORD) and the end of the war in Europe.
Interpretation of strategic PR was undertaken by a Central Interpretation Unit (CIU) at RAF Medmenham, later to become an Allied unit (ACIU). When a PR sortie landed the film was developed at the airfield and selected prints were interpreted immediately. The film was then transferred to the ACIU for ‘second phase interpretation’, where a more detailed general analysis was produced within 48 hours. Third phase interpretation then took place in specialist sections, each of which was trained to look for more specific information on a particular subject, such as airfields.
The interpretation of photographs at the ACIU relied heavily on stereoscopic techniques which reproduced a three-dimensional image from a two-dimensional photograph, by mimicking the human brain's merging of twin images. Each camera was automatically set to take photographs with a 60% overlap of the previous print and two prints could be arranged side-by-side to produce a single image when viewed through a stereoscopic magnifier. The aircraft's forward momentum caused a difference in the angle at which the two photographs had been taken, and this gave the appearance of a 3-D image when viewed through the stereoscope, which was of great benefit in enabling the interpreter to identify objects and pick out important detail. Difficulties caused by the blurring of images on low-level photographs as a result of the aircraft's forward movement were overcome by using cine film in forward-facing cameras with the pilot flying directly at the target.
The vertical cameras in RAF aircraft were usually mounted in pairs at a slight angle to cover twice the ground in one pass and give a 10% sideways overlap. Later in the war forward-facing oblique cameras were mounted on each wingtip to give stereoscopic low-level cover. The RAF was hampered early in the war by having cameras with short focal length lenses, which gave small-scale prints and made interpretation difficult. Gradually bigger cameras were introduced with larger lenses and a greater number of exposures. In 1942 cameras were introduced capable of producing photographs of 1/10,000 scale from 9,150 m. (30,000 ft.): a scale suitable for detailed interpretation.
The intelligence available from the photographs was used in planning by all three services. Bomber Command's operations over Europe relied on PR cover for pre-raid briefings and post-raid assessment of results (see also
Butt report). Later in the war, when oil and transportation targets were being systematically attacked, PR cover was essential. Sorties were also regularly flown on behalf of the navy, to establish the whereabouts of German naval and merchant shipping. During the campaign against the
V-weapons PR provided intelligence on their development, including dimensions, and the location of the launching sites. Between 1 May 1943 and 31 March 1944, 40% of all Allied PR sorties were directed against the V-weapons programme, and a total of 1.25 million photographs were taken. PR also provided vital information on German
radar and anti-aircraft defences for Bomber Command and others. Centralized interpretation, regular coverage, and integration with other intelligence allowed interpreters to identify interesting or unusual developments for further investigation.
When the USA entered the war the Americans quickly recognized the merits of the British system, and adopted it for their own use. Interpretation for the US Army Air Forces (USAAF) strategic offensive was concentrated at Medmenham in an integrated unit. As with other nations in the pre-war period, the USA had short-range reconnaissance units equipped with slow and obsolescent aircraft, and longer range PR was to be undertaken by bomber aircraft equipped with suitable cameras. Drawing on British experience the Americans were quick to adapt the P38 Lightning and P51 Mustang as reconnaissance aircraft. In the
Pacific war, where distances were greater and the opposition less formidable, the USAAF also used reconnaissance versions of the B24 and B29 to provide strategic cover for the war with Japan.
In the two years which followed the Japanese attack on
Pearl Harbor in December 1941, US airmen, using a camera which could take an area 48 by 14.5 km. (30 by 9 mi.) in one shot, mapped 21 million square kilometres (8 million square miles) of the earth's surface. This was done at high altitude, but they also flew at 100 m. (300 ft.) with continuous-strip cameras to map invasion beaches and, using flashlight bombs which generated a billion candlepower, they were able to photograph Japanese movements at night. The results were so detailed that it was possible to identify ships by name and new aircraft types on the ground. So valuable was PR to US forces in the Pacific that the commanding general of the USAAF,
General Arnold, commented that ‘a camera mounted on a P38 (Lightning fighter) often has proved to be of more value than a P38 with guns’ ( Moeller, p. 192).
The Luftwaffe had entered the war with some 80 reconnaissance squadrons, and a similar approach to the Allies. Tactical units were equipped with the Henschel Hs126, similar to the Lysander. Longer-range PR squadrons were equipped with the Dornier Do17F, or the Junkers Ju88D. The Luftwaffe also developed the high-altitude Ju86P, which operated in limited numbers over the UK, the Middle East, and the USSR. The Luftwaffe also followed the Allies in deploying reconnaissance versions of single-engined fighters. However, with the exception of the unarmed but slow Ju86P, the Luftwaffe never adopted the Allied philosophy of removing the armament to increase range and performance, and flying high-altitude profiles. Hence, when air superiority was lost, as it was over the UK, PR was severely restricted or non-existent. This meant a lack of comparative cover, which was dependent on repeated sorties, and the photographs obtained were often of limited value. Once the British produced fighters capable of downing the pressurized Ju86Ps in 1942, Luftwaffe PR in the west became almost totally ineffective.
On the Eastern Front, Luftwaffe long-range PR continued to operate, and utilizing short-range aircraft such as Focke Wulf Fw189s, Fw190s, or Messerschmitt Bf109s, tactical reconnaissance remained effective until much later in the war. However, German PR was hamstrung by organizational weakness. Each
Luftflotte HQ was responsible for all PR and interpretation in its area, and co-ordination was often poor. Furthermore, although there was a central photographic unit, interpretation was decentralized, and interpreters seldom rose above the rank of senior NCO. As a result interpretation often took the form of searching only for the information which had been specifically requested. Little detailed analysis comparable with the ACIU's third phase interpretation was undertaken and, because of the lowly status of the work, interpreters were frequently unaware of the intelligence available from other sources which would have assisted their interpretation. In addition the Germans tended to use larger and heavier, though technically excellent, cameras, and they never developed the range of cameras and techniques employed by the Allies. German interpreters often worked from negatives, which meant that they could not use stereoscopic techniques and their work lacked detail. Therefore, while tactical and topographical PR was adequate strategic reconnaissance frequently was not. As a result German intelligence in such areas as Allied preparations for OVERLORD, the accuracy of the V-weapon bombardment, and the whereabouts of British capital ships was frequently poor. Misled by their early success, the Germans never developed the philosophy or equipment to emulate British success in the face of enemy air superiority.
In the USSR much emphasis had been laid on the importance of PR in pre-war manuals, but in 1941 the gap between theory and practice proved immense. As with other countries the Soviets rapidly discovered that obsolescent aircraft such as the Polikarpov Po2s were too vulnerable. The first Soviet unit equipped with the more effective Petlyakov Pe2 was not formed until November 1941. German air superiority and poor Soviet aircraft and equipment meant that little effective PR could be performed for some time, and the absence of trained interpreters before April 1942 also severely hampered their efforts.
As the war went on and the aircraft, equipment, and personnel improved, so did Soviet effectiveness. Concentrating almost exclusively on reconnoitring German army dispositions within 800 km. (500 mi.) of the front line, the Soviets concentrated on roads, railways, and military dumps and concentrations. By the later phases of the war such areas on the axes of a Soviet advance would be photographed several times before any attack. Even so progress was slow and the Soviets remained heavily reliant on visual observation. During the
Kursk operations in 1943 only 40% of Soviet reconnaissance flights were capable of taking photographs. However, by the end of the war Soviet PR units were capable of providing effective intelligence. The proportion of PR to visual reconnaissance rose from 10% in 1941 to 87% in 1945 and during the course of the war Soviet pilots photographed 6.5 million square kilometres (2.5 million square miles) of land.
By 1945 PR had become far more advanced both technically and in its ability to provide intelligence. Among the operations to which it contributed vital intelligence were the
Bruneval raid, the
Peenemünde raid, the OVERLORD landings (before which more than 4,500 PR sorties were flown), and the Allied
strategic air offensives. On the Eastern Front first the Germans, and then the Soviets, used it to assess the opposing defences, often with great accuracy.
Sebastian Cox
Bibliography
Brookes, A. , Photo Reconnaissance (Shepperton, 1975).
