Behind the engine-carrying body (fuselage or nacelle) a turbulent region or wake is formed as the airplane flies. The exhaust moisture and some of the engine heat are discharged into this wake and become diffused throughout the wake as a result of the mixing action of the turbulence. The moisture and heat do not, however, mix with the air outside the wake because there the air is "smooth.'...

It is easy to see that, if the air is so cold that it cannot hold much water as vapor, the water in the exhaust may be sufficient, when added to the moisture already in the atmosphere, to raise the humidity in the turbulent wake to or beyond the saturation value. If this condition exists, some of the water vapor will condense and a visible trail will form.

Richard V. Rhode and H. A. Pearson, Condensation Trails, NACA Wartime Report, September 1942 (1)

Introduction

As we saw in the first part of this paper, contrails were observed as early as October 1918. Yet, they remained a rare phenomelatively little interest across the 1920s and 1930s, despite developments that steadily raised the operational ceiling of military aircraft. By the time of the Spanish Civil War, state-of-the-art fighters could engage in combat in the upper regions of the troposphere where engine exhausts routinely turn into contrails. Francisco Tarazona's September 1938 report of contrails generated by dogfighting aircraft was a harbinger of things to come.

Within a year of Tarazona's report, Germany plunged Europe into a general war when she invaded Poland. In the months between the fall of Poland and the German invasion of France in May 1940, German pilots clashed in desultory combat with French and British airmen as both sides flew patrol and reconnaissance missions over Western Europe. (2) From these air operations and those that took place when Germany overran France in the spring of 1940, it was apparent that contrails were intrinsic to modern air combat and had important operational implications. These early months of the air war also spawned what may be the first published account of contrails in air combat.

The Battle for France and Saint-Exupery's Train of Frozen Stars

At the time Germany invaded France, French aviation pioneer and famed author Antoine Saint-Exupery was just short of his fortieth birthday, well past the age when men were considered fit for air combat duties. Given his age, his literary achievements, and health problems caused by earlier aircraft accidents, Saint-Exupery was not expected to volunteer for combat duty and could easily have honorably avoided it. However, he believed France was in grave danger and that all Frenchmen who could were obliged to come to her defense. (3)

True to his convictions, Saint-Exupery managed to secure an assignment flying reconnaissance planes, specifically, the Potez 63. Such an assignment was a serious challenge for a man of his age and physical condition due to the difficulties and discomforts associated with flying in the cold cockpits of high altitude aircraft. (4)

Saint-Exupery...