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Description
Judging by the wakes of vapor and the lines of tracers left behind in the high, cold air, the Messerschmitts are mixing it up with Number 4 Squadron.
Francisco Tarazona, Yo Fue Piloto de Carza Rojo, September 1938. (1)
Introduction
Contrail is a contraction of condensation trail, an early term applied to the thin, white clouds that appear behind aircraft when moisture in engine exhausts forms ice crystals in cold air that is already sufficiently saturated. Vapor trail was another early term applied to this phenomenon.
Although ubiquitous today, condensation trails were apparently unknown until World War I. Indeed, what may be the earliest reported observations of contrails were made in the autumn of 1918, as the Great War was drawing to a close. By the end of 1920, other sightings had been reported and several people had advanced preliminary explanations of the new phenomenon. Yet, until the opening days of the Second World War, contrails would remain an isolated phenomenon generally unknown to the public and of limited interest to military aviators.
This situation changed suddenly and dramatically during the first days of World War II. The key to this change was a revolution in aviation that took place across the decades of the twenties and thirties, as leading aviation powers, spurred on by air power enthusiasts, worked to expand the operational envelope of combat aircraft. Because of this revolution, when the Second World War opened, the world's most powerful air forces were flying warplanes with operational ceilings in excess of 25,000 and even 30,000 feet, well into the atmospheric region where conditions are often favorable to contrail formation. As a result, these aircraft routinely trailed what aviation pioneer and writer Antoine Saint-Exupery poetically called "pearly white" scarves as airmen executed their missions in the skies high over Western Europe.
Today, we associate three main types of condensation phenomena with flight. One of these is the spiraling, ribbon-like streamers that can appear in wingtip vortices under the proper atmospheric conditions. Another type is the spectacular cone-shaped Prandtl-Glauert condensation cloud that can form around the waist of high-speed aircraft. Finally, there are the long, thin, clouds spawned by aircraft engine exhausts--the common contrails that crisscross the skies over much of the world today. This last form of condensation phenomenon is the focus of this two-part paper.
Part I covers the period from the end of World War I to the eve of World War II. It begins by describing some early contrail sightings and then discusses the explanations prompted by these observations. This is followed by a review of the major developments that made high altitude flight part of routine combat operations and led to the first recorded observation of contrails in combat, this coming during the Spanish Civil War, Europe's dress rehearsal for World War II.
Part II focuses on the role of contrails in European air operations between 1939 and 1945. It also discusses British and American efforts to understand contrails so that Allied airmen could take advantage of contrails in combat operations or at least prevent enemy airmen from doing the same.
The Argonne Battle Cloud: Early Contrail Sightings
The First World War started in 1914, a little over a decade after Orville Wright coaxed his frail, primitive flying machine aloft for a twelve-second flight that covered a scant forty yards, about the length of a long pass in the National Football League. (2) Given the immaturity of aviation technology, it is not surprising that European powers opened the war with small air forces comprised of planes that were so slow that they could scarcely keep pace with today's freeway traffic. Moreover, these planes were open-cockpit machines that were generally limited to altitudes below 12,000 feet. By the end of the war, however, frontline aircraft could reach speeds of 130 mph and operate as high as 20,000 feet. (3)
While this operational ceiling is still below the band between 25,000 and 40,000 feet where atmospheric conditions are most often conducive to contrail formation, (4) planes flying at 20,000 feet and even lower can generate contrails under the proper conditions of temperature and humidity. Therefore, in the later stages of the Great War, contrail-generating flights would have become increasingly common as the operational ceilings of first-line aircraft increased. Given the number of planes flying over the Western Front and the number of men on the ground with a vital interest in watching the skies for hostile aircraft, it was virtually inevitable that substantial numbers of people would eventually notice that at least some high-flying planes were producing long thin clouds as they crossed the skies.
In early October 1918, while the American Expeditionary Force was engaged in the Meuse-Argonne offensive, several hundred AEF members noticed a number of strange clouds that seemed to emanate from high-flying aircraft and stretch across much of the sky. Three of these observers thought the phenomenon unusual enough to take special note of it. After the war the three independently brought their observations to the attention of the public.
The first of the three to have his account of the strange clouds published was Captain Ward S. Wells, Army Medical Corps, who was serving with the 60th Infantry, 5th Division, American Expeditionary Force, during the Meuse-Argonne campaign. In early October 1918, Ward and his unit were in the Bois de Hess just back of Montfaucon, about ten miles to the west and a little north of Verdun, where they were waiting to take over a portion of the front. 5
Ward noted that it had been raining for several days when at last there dawned "a wonderfully clear and beautiful morning, with not a cloud in sight." During this particular morning, according to Ward,
Our attention was first drawn to the sky by the sudden appearance of several strange and startling clouds--long, graceful, looping ribbons of white. These were tapering to a point at one end and at the other where they dissolved into nothingness 60 degrees across the sky, were about as broad as the width of a finger held arm's distance from the eye. On close observation we noticed some distance ahead of each cloud point the tiny speck of a chasse [sic] plane.... [N]ever before had I seen a plane writing in white upon the blue slate of sky. (6)
Wells had described his observations in a letter to his brother Everett Wells. Because he considered the phenomenon described by Ward to be "quite unusual and perhaps worthy of record," Everett himself wrote to Scientific American quoting at length from Ward's letter. An editorial note at the end of the letter echoed Everett's sentiments: "The observation of clouds formed in the wake of an airplane is, so far as we know, novel. Perhaps some of our readers can bring forward other examples of this, ..." (7) Such a comment coming from the editor of a scientific journal who presumably had a broad, general knowledge of scientific affairs suggests that we are here close to the earliest report of a contrail sighting.
A little over a year later, George B. Vaughn, apparently unaware of Wells' earlier letter, asked if any reader of The American Legion Weekly might be able to explain to him "a phenomenon that occurred, I believe, on October 10, 1918, over the battle front" in the vicinity of Montfaucon. Vaughn and his comrades were passing through a small town
when we noticed three thin parallel lines of clouds or smoke stretching far across the sky. They looked as if they had been made by three planes passing, throwing out smoke and cutting stunts, for the lines were far from straight....
Hundreds of troops were watching this display and wondering what had caused it.
Vaugh noted that some of those who saw the phenomenon believed that it was some kind of mirage, while others thought it might be "something new by the Germans." (8)
A month later, Walter N. Nead responded to Vaughn's query. Formerly a captain in the 168th Infantry Regiment of the 42d Rainbow Division, Nead described what may be the same occurrence of contrails that had prompted the reports of both Wells and Vaughn:
I would relate that the Rainbow Division, on the morning of October 10, 1918, was lying in what had at one time been a wood just back of Montfaucon. The sky was clear except for a few fleecy clouds to the northwest. Three airmen came from the northwest and passed almost over our regiment, continuing on to the southeast.
Behind each machine was a trail of white, which at first sight seemed to be smoke resulting from poor engine combustion but which upon more careful observation proved too wide to have been caused by smoke. Perhaps the strangest thing of aU was the fact that when the planes reached a certain point in the sky the rainbow (sundog) colors (9) became distinctly visible.
The editor's of The American Legion Weekly titled Nead's letter: "The Argonne Battle Cloud." (10)
There are at least two other reports of contrail sightings that predate 1920. Both took place in Germany. One was written by Alfred Wegener, a German polymath who not only had a PhD in astronomy but also exhibited wide-ranging interests in geology and meteorology. It was Wegener who first advanced the theory of continental drift which he codified in his 1915 book The Origins of Continental Drift. Wegener reported his contrail sighting in a German meteorological journal at the beginning of 1920, making it likely that the observation took place near the end of 1919. According to Wegener, "during three airplane flights over Munich at a height of 9 km. a cloud 50 km. in length was formed." Wegener also presented an explanation of contrails of which more anon. (11)
The second German sighting occurred on May 9, 1919, when a pilot flying over Berlin at about 26,000 feet noticed the generation of a cloud stream that extended for about forty miles behind his plane. This stream eventually spread out to form a cloud layer that was about 3,000 feet thick. The pilot saw a similar phenomenon two days later. (12)
It may seem odd that word of the May 1919 sighting was not published until 1930, when Nature reported the episode in its section on Historic Natural Events. Given the dates of other events reported here (e.g., May 6, 1915, May 8, 1663, and May 8, 1902), it appears that this section was used by journal editors to inform readers of unusual phenomena that might have come to light only recently. (13) More will be said on this point at the end of the following section.
Early Explanations
Because of their novelty, the Argonne battle clouds demanded an explanation. The explications offered may be grouped into three broad categories. The first is an argument from analogy that assumed the long cloud trails were essentially a familiar phenomenon... |
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