Second World War
In 1928, the Royal Air Force (RAF) developed an electrical heating system for aerial cameras, allowing photographs to be taken at high altitude without the components freezing. In 1939, Sidney Cotton and officer Maurice Longbottom proposed that aerial reconnaissance be carried out with small, fast planes, capable of flying high to avoid detection or interception, an innovative idea for the time.
Thus was born the reconnaissance version of the Spitfire (Spitfire PR), unarmed and with additional cameras and fuel tanks. These planes reached 396 mph and 30,000 feet altitude, and carried up to five heated chambers (as opposed to the cockpit). Its success was such that multiple variants were built exclusively for reconnaissance, operating with the Photographic Reconnaissance Unit No. 1.
Other fighters were also adapted, such as the British Mosquito and the American P-38 Lightning and P-51 Mustang. These aircraft were often painted in special colors (PRU blue or pink) to camouflage themselves in the sky, and in many cases their weapons were removed or their engines were modified to perform better at high altitudes (over 12,000 m).
The American F-4, a factory modification of the Lockheed P-38 Lightning, replaced the four nose-mounted machine guns and cannon with four high-quality K-17 chambers. Approximately 120 F-4s and F-4As were hastily available by March 1942, arriving at the 8th Photo Squadron in Australia in April (the first P-38s to see combat). The F-4 had the advantage of long range, high speed, and high-altitude flying capabilities; a powerful combination for recognition. In the second half of 1942, Lockheed produced 96 F-5As, based on the P-38G, and all subsequent photo-reconnaissance versions of the P-38 were designated F-5. In its reconnaissance role, the Lightning was so effective that Lockheed delivered more than 1,200 F-4 and F-5 variants, serving as the primary photoreconnaissance aircraft of the United States Army Air Forces (USAAF) throughout the war in all theaters of operations. The F-6 Mustang arrived later in the conflict and, by the spring of 1945, became the USAAF's primary reconnaissance aircraft in the European theater. American photographic reconnaissance operations in Europe were centered at RAF Mount Farm, and the resulting photographs were sent to Medmenham for interpretation. Approximately 15,000 Fairchild K-20 aerial cameras were manufactured for use on Allied reconnaissance aircraft between 1941 and 1945.
The British de Havilland Mosquito excelled in the photographic reconnaissance role; The converted bomber was fitted with three cameras installed in place of the bomb bay. It had a cruising speed of 255 mph, maximum speed of 362 mph, and a maximum altitude of 35,000 feet. The first converted Mosquito PRU (Photographic Reconnaissance Unit) was delivered to RAF Benson in July 1941 by Geoffrey de Havilland himself. The PR Mk XVI and later variants had pressurized cockpits, as well as pressurized center and inner wing tanks to reduce fuel vaporization at high altitude. The Mosquito was faster than most enemy fighters at 35,000 feet and could operate almost anywhere. Colonel Roy M. Stanley II of the US Air Force stated of the aircraft: “I consider the Mosquito the best photo-reconnaissance aircraft of the war.” The USAAF designation for the reconnaissance Mosquito was F-8.
Aside from the Mosquito, most World War II bombers were not as fast as fighters, although they were effective for aerial reconnaissance due to their long range, inherent stability in flight, and ability to carry large camera loads. American bombers with top speeds less than 300 mph used for reconnaissance include the B-24 Liberator (photo-reconnaissance variant designated F-7), the B-25 Mitchell (F-10), and the B-17 Flying Fortress (F-9). The revolutionary B-29 Superfortress was the world's largest operational bomber when it appeared in 1944, with a top speed in excess of 350 mph, which was remarkable for such a large and heavy aircraft; The B-29 also featured a pressurized cabin for high-altitude flight. The photographic reconnaissance version of the B-29 was designated F-13 and carried a set of cameras composed of three K-17B, two K-22 and one K-18, with the possibility of adding others; It also maintained the standard defensive armament of the B-29 with a dozen .50 caliber machine guns. In November 1944, an F-13 made the first flight by an Allied aircraft over Tokyo since the Doolittle Raid in April 1942. The Consolidated B-32 Dominator was also used for reconnaissance over Japan in August 1945.
The Japanese Army's Mitsubishi Ki-46, a twin-engine aircraft designed expressly for reconnaissance and equipped with a light machine gun for defense, entered service in 1941. Codenamed “Dinah,” this aircraft was fast, elusive, and difficult for Allied fighters to destroy. More than 1,500 Ki-46s were built, and their performance was improved later in the war with the Ki-46-III variant. Another reconnaissance aircraft designed specifically for the Imperial Japanese Navy was the single-engine, carrier-based Nakajima C6N Saiun (“Iridescent Cloud”). Nicknamed “Myrt” by the Allies (World War II), the C6N first flew in 1943 and was also very difficult for American fighters to intercept due to its excellent performance and speed close to 400 mph. On August 15, 1945, a C6N1 was the last aircraft shot down in World War II.
The Luftwaffe "Luftwaffe (Wehrmacht)") began deploying jet aircraft in combat in 1944, and the twin-engine Arado Ar 234 Blitz (“Lightning”) was the world's first operational jet bomber. The Ar 234B-1 was equipped with two Rb 50/30 or Rb 75/30 cameras, and its top speed of 460 mph allowed it to evade Allied non-reaction-powered fighters. The Junkers Ju 388, a twin-engine high-altitude bomber, was a final evolution of the Ju 88 through the Ju 188. The Ju 388L photo-reconnaissance variant had a pressurized cockpit, retaining the original multi-role design of the Ju 388, intended as a bomber, night fighter and bomber destroyer, due to the RLM's perceived threat from the American B-29 (which was ultimately not deployed to Europe). Approximately 50 Ju 388Ls were produced under very adverse conditions towards the end of the war. As with many other advanced weapons introduced by Nazi Germany, the logistical circumstances of the war had already changed too much by the end of 1944 for these aircraft to have any significant impact.
The DFS 228 was a rocket-powered high-altitude reconnaissance aircraft that was under development in the latter stages of World War II. It was designed by Felix Kracht at the German Institute of Glider Flight (Deutsche Forschungsanstalt für Segelflug), and conceptually is an interesting precursor to the post-war American U-2, as it was essentially a powered long-span glider, designed exclusively for high-altitude aerial reconnaissance. Its advanced features included a pressurized escape pod for the pilot. The aircraft never flew with rocket propulsion; Only flights with glider prototypes were made before May 1945.
The collection and interpretation of aerial reconnaissance intelligence became a considerable task during the war. By early 1941, RAF Medmenham was the main center for photographic reconnaissance operations in the European and Mediterranean scene. The Central Interpretation Unit (CIU) was later merged with the Damage Assessment Section of Bomber Command and the Night Photographic Interpretation Section of No 3 Photographic Reconnaissance Unit, RAF Oakington, in 1942.
Between 1942 and 1943, the CIU expanded and participated in the planning of virtually all military operations, playing a crucial role in intelligence. By 1945, some 25,000 negatives and 60,000 photographic prints were processed daily, reaching a total of 36 million prints during the war. The visual archive contained 5 million images and had generated 40,000 reports.
On May 1, 1944, with increasing American participation, the unit was renamed the Allied Central Interpretation Unit (ACIU), with more than 1,700 personnel. Among its members were performers recruited from Hollywood film studios (such as Xavier Atencio) and renowned archaeologists such as Dorothy Garrod and Glyn Daniel.
Sidney Cotton, a pioneer in aerial photography, developed advanced high-altitude, high-speed photography techniques, which helped identify key targets. At their peak, British reconnaissance flights generated up to 50,000 images a day.
The use of stereoscopic imaging was essential in uncovering secret German facilities, such as the V-2 rocket development plant at Peenemünde and launchers at Wizernes and 96 other locations. Swiss equipment such as Wild stereoautograph machines were used to accurately measure and build physical models for analysis.
Medmenham's greatest success was Operation Crossbow, launched on 23 December 1943, which destroyed the V-1 missile launch infrastructure. Aerial photographs helped identify both the V-1 and V-2 launch mechanisms, according to expert R.V. Jones.