Lighting the Skies

Someone stated in the early days of the war, a feeling that was reciprocated by the soldier in khaki and the sailor in blue, that a mechanical device would be the determining factor in ending the world conflict, favorably, of course, for the United States and her allies. 1

One of my common topics is the history of nuclear weapons. The "atom bomb" is a rich vein of history because its impact has been as much cultural as technical. Dramatic depictions like Christopher Nolan's Oppenheimer have recently enforced, perhaps even revived, the perception of nuclear weapons as an innovation that forever changed warfare. More quietly, historians and strategists tend to wonder if that is still true today, or if it was ever as true as was supposed—the conventional firebombing of Tokyo probably claimed as many victims as the nuclear attacks on Hiroshima and Nagasaki, for example. Besides, it's not unusual to hear people overstate the significance of nuclear weapons to WWII in a way that is obvious with a brief inspection of the timeline. The technology became available only very late in the war, and for that reason if no other, it must have had less of an impact on the outcome than other revolutionary wartime developments like radar.

Why is it that radar, a complex technology that fundamentally changed the landscape of aerial combat, seems so pedestrian? Perhaps because the technology has far more non-military applications, and so is more familiar to our everyday lives. Perhaps because the development of radar was scattered between countries and institutions without the involvement of such intriguing figureheads as J. Robert Oppenheimer (although one wonders if this is because we have not looked as close; certainly radar figures like Henry Tizard had colorful lives as well). Perhaps because radar just isn't as exciting: it does not put on anything like the show of a nuclear detonation.

Today, we consider another such step in military technology. This is an invention that forever changed the battlefield, and it's one that does put on a show. In fact, that has become the technology's main purpose. From the 1870 siege of Paris to the modern used car lot, searchlights have marked many of history's great conflicts—and great deals.

The concept of electric light has been known since the very early 19th century. An electric arc lamp, or at least one of their ancestors, was demonstrated in 1806. Because of the widely known story of Thomas Edison's incandescent lamp, most people know that electric light had a very difficult journey from idea to practical device. That path was not as simple as what we are taught in schools: besides the several other inventors with a good claim to the lightbulb, incandescent lights were just one of a few technologies that developed in parallel.

Before controlled incandescence, the principal form of electric light was still an arc. Arc lamps also did not fall to incandescent bulbs as quickly as you might think. Arc lamps remained the preferred choice for very bright, high-CRI lighting into the mid-20th century, and reached what will likely remain their ultimate form in the late 1960s, as the 15 kW Xenon arc lamps used by IMAX projectors. Along the way, arc lamps displaced many of the early forms of artificial lights: Oxy-hydrogen candles, known as "limelights," fell out of theatrical use. "Moonlight towers" began the displacement of gas lights for street lighting.

And the military—the military readily adopted this new form of reliable, practical, powerful lighting.

The effect of artificial lighting on military tactics could fill a book. I will focus on one narrow part of this story, but it will be helpful to set the stage with a few of the earlier developments. For much of the pre-electricity era of military history, artificial lighting was mostly a disadvantage. Fires, torches, and other practical sources of light were bright enough to reveal one's location but not bright enough to search anyone else out. Ironically, the main interest that military researchers had in light was often to suppress or conceal it.

The chemical light technology developed for theaters and displays had promise, though. One of the first recorded uses of a powerful light for a military venture (and, as far as I can tell, the very first recorded use of a searchlight) came in the context of the American Civil War. The Union Navy sought to economically attack the Confederacy by maintaining a persistent blockade on southern ports; the Confederacy sought to maintain trade, often by sending out "blockade runners" under cover of night. A Union ship, perhaps frustrated by firing aimlessly into the dark, improvised: a theatrical light was mounted to a crude reflector, forming the first naval searchlight. It wasn't a very good one, it was dim and unfocused and the sailors struggled even to keep it lit under maritime conditions. It was good enough, though. By first following the sound, and then casting the light, the Union ship was able to engage the Confederate vessel even on a moonless night. Amusingly, while this incident is widely described in histories of military signals and lights, I have found none that state the outcome. Perhaps it was unfavorable to the victors.

Electric arc lamps were far more suitable to military use: simpler to operate (although not as simple as we might today expect), more flexible in their placement, and by the end of the Civil War brighter. The 1870 Siege of Paris, part of the Franco-Prussian War, was a bellwether in the history of military aviation. Cut off on the ground, the French made extensive use of balloons (a technology they had pioneered in the 18th century) to move people and mail. In the process, several records for aerial travel were set. The French enjoyed air superiority and had little need for air defense, but the situation on the ground was much more troublesome. Prussian forces mounted lengthy artillery bombardments, causing devastation limited mostly by the range of their cannons. For the soldiers manning Paris's fortifications, it was important not only to keep attackers outside of the city, but to keep them as far away as possible.

Paris, not for nothing known as the "City of Light," had seen demonstrations of arc lamps back to 1850. The invention of the arc regulator (which advanced the carbon rods to keep the arc intact) and improved batteries made the lights more practical by 1870, and during the early days of the siege "electricians" were hastily recruited to the city's defense. They manned a variety of arc lamps installed around the city, limiting the cover of darkness for nighttime assaults. At the summit of Montmartre hill, a position with a clear view over one of the most vulnerable parts of the city's defense, they installed one of the most impressive lights ever built. Not only was it larger than the others, it could operate for longer: the power supply was not a battery, but a dynamo powered by a steam engine. Besides that leap into modern design, the Montmartre light also presents an early example of "tipping and cueing" in intelligence gathering. French intelligence agents, having caught wind of a surprise attack, sent a message to Montmartre where the light's skilled operators aimed it by heading and elevation before applying power to catch the enemy in quite a compromising position.

A decade later, the military searchlight had become a standard technology. The Royal Navy regularly equipped ships with dynamo-powered, carbon-arc searchlights starting around 1882. They found that, besides their role in aiming weapons, searchlights could be something of a weapon on their own. Aiming searchlights back at coast defense artillery positions not only exposed them to incoming fire, it also dazzled the gunners and frustrated their efforts to accurately aim at the ships. This principle was memorably demonstrated by a 1903 US joint maneuver exercise, in which the Navy's Atlantic Fleet mounted a simulated attack on Long Island Sound. All together, on cue, the ships trained their searchlights on the main defensive battery at Fort Michie. The soldiers at the fort didn't manage a single shot, they were so blinded by the lights—and limited in their ability to even move around the battlements, since they could so plainly be seen (and fired upon).

As the military developed searchlights, they were quickly applied to civilian use. Limited availability of electricity, and limited need for such powerful lighting, meant that searchlights wouldn't yet become part of the urban landscape. They were reserved for special events, especially those with an emphasis on technical demonstrations. Of course, such events were bounteous around the turn of the century in the form of various world fairs and expositions. Perhaps the first use of searchlights as a device for entertainment came at the 1893 Chicago World's Fair, which was extensively lit by electricity. A total of 17,000 horsepower of steam engines (so, yes, presumably steam horsepower, a curiously different unit from the one we are familiar with today) powered thousands of arc lights.

Most of these were for illuminating the fairgrounds and its many monuments, but some were installed for the sake of light itself. On the roof of the Liberal Arts Building, a searchlight claimed to be the most powerful yet made could light a newspaper well enough to comfortably read at a distance of eight miles. Of course, it was more than just a book light—it was a way to attract attention. Unlike the military context, civilian searchlights were deployed specifically to be seen. Rooftop searchlights became a common feature of large expositions, and by lazily searching the sky they established an atmosphere while guiding curious onlookers to the site of the event.

Even this early, it was known that searchlights could be a powerful form of advertising. At the Chicago World's Fair, the upstart Cloud Projector Company demonstrated a searchlight with a lens system that could focus a slide onto the cloud layer. It was literally a cloud projector, in the modern sense, and giant words floating ethereally in the sky announced the fair's upcoming special events.

In 1901, the Pan-American Exposition was underway at Niagara. Among the attractions was a demonstration of electrical arcs produced by a 40 kV transformer recently installed at the Niagara Falls power station. Alongside that light show, a second, more controlled form of arc was displayed: searchlights. These were described as an application of military technology, and specifically of military signaling technology. Searchlights were installed atop the "Electric Tower" at the exposition grounds, and at a viewing tower erected at Niagara Falls proper. At night, the two lights—22 miles apart—were each plainly visible from the other tower. The military was, of course, well aware of this potential use and as soon as searchlights had been installed on Navy ships they came into use as a means of communication.

Extensive newspaper coverage of the Exposition means that we know more details of these machines. The searchlights used for the tower demonstrations had 30" reflectors, and consumed 80 amps at about 50 volts for 4 kW give or take. This was indeed a very bright light for the time, and at the Exposition, the searchlights were swung around among various targets. "As the beams of the projectors sweep across country," The Virginian-Pilot wrote, "the residents of the villages and country places will enjoy the illumination." Excitement for the lights was such that newspapers throughout the region published Morse code tables, in the hope that anyone in the region could decipher news bulletins that were sent from the signal lights.

Electric light is far from the only invention to make a dual appeal to spectacle and the military. From the Wrights' first controlled flight in 1903, it only took about seven years for the Navy to envision the aircraft carrier. The 1911 Italo-Turk