This is from a folder of notes by G. A. Wieczorek, a Signal Corps officer during WWI and an instructor at the Second Corps Signal School at Chatillon-sur-Seine. These are notes regarding using radio with observation from aircraft, one of the first military uses for both radio and airplanes.

Radios evolved dramatically during the first World War, partly because they needed to be small and light enough to be crammed into aircraft. Still they were fiddly things, and flying a wood and canvas plane while constantly adjusting spark gap radio equipment AND trying to avoid being shot down was no small task.

This definition of radio from the 1918 Ellington Field yearbook sums up the situation well.

Radio is the science whereby a pilot, in the leisure seized in the quiet moments of combat with eighteen enemy planes, while under a rattling archie fire, communicates to his commander the complexion, civil occupation and beer preference of a Hun 15,000 feet below.

“Archie” was British (and later American) slang for anti-aircraft guns.