Reported in Scientific American, this Week in World War I: September 25, 1915
Considering how flying, even in the earliest years of the era of flight, seems high-tech, and despite the fact that the first trans-Atlantic wireless message was sent in 1901, it is curious to see flying machines in 1915 having to rely on communication technology that seems not too far advanced from smoke signals. Our article from this week 100 years ago says:
“In considering means of signaling from airships one's first thought would be to turn to wireless telegraphy, but on account of the many troubles experienced with same, it became necessary to search for some other and more practical means for communication with the observation stations.”
One of the most useful roles for aircraft and airships in the First World War was for reconnaissance. It was all very well to record information while flying, then wait to land to make a report, but it was more useful to be able to give instantaneous reports while still in the air over the target. But the first wireless sets for installation in aircraft, developed by the middle of 1915, were heavy, had a short range and were fragile—not useful traits for military aircraft then or now.
The French devised a stop-gap system using a 5-gallon cylinder filled with lamp black (a very finely powdered black substance). The container could puff out small clouds of lamp black in a Morse code pattern. Range was limited, it could only be used in daylight, and of course the pilot could not receive replies [see top image].
The Germans “did not adopt this method, but are using a more practical system invented by the German scientist, Donath.” For signaling from airships, a lamp attached to batteries could flash out Morse code messages by day or night. “The efficiency was tested on the Johannis-Thaal aviation grounds, and it was found that at night signals could be sent a distance of 10 miles, and in the brightest daylight signals could be distinguished over five miles.”
By 1916 more robust and lighter wireless sets for aircraft were being produced by all sides in the conflict, and these stopgap measures were obsolete.
Our full archive of the war, called Scientific American Chronicles: World War I, has many articles from 1914–1918 on the trench war on the Western Front. It is available for purchase at www.scientificamerican.com/products/world-war-i/