Tucked between articles on latitude observations and multiplex topography, the April 1945 issue of Surveying and Mapping — the quarterly journal of the American Congress on Surveying and Mapping — lists a paper that reads like steampunk science fiction:

The Use of Balloons and Radios in Mapping — WM. T. RYALL

The journal was the professional organ of American surveyors, edited that year by A. L. Shalowitz of the U.S. Coast & Geodetic Survey, and presided over by George D. Whitmore of the Tennessee Valley Authority. Its regional vice presidents were scattered from Edmonton to Atlanta to a man named Lewis A. McArthur at Pacific Power & Light in Portland — a snapshot of a profession that was, in 1945, in the middle of inventing how to see the Earth from above.

Before GPS satellites, before lidar drones, before even reliable aerial photography from fixed-wing aircraft over hostile or roadless terrain, surveyors faced a maddening problem: how do you fix a point on the ground when you can't physically chain or theodolite your way to it? The answer, in the 1940s, was startling. You floated a balloon — sometimes tethered, sometimes free — carried a radio transmitter aloft, and triangulated the signal from multiple ground stations. The balloon became a moving control point in the sky. Photogrammetric crews used balloons to lift cameras over jungle and swamp. Hydrographers used radio fixes — Shoran and later Loran — to position survey vessels miles offshore where sextants and landmarks failed.

What makes this forgotten is not that we abandoned the principle — we did the exact opposite. Every time your phone gets a GPS lock, it is doing the same thing Ryall described: triangulating a radio signal from a transmitter floating high above the ground. We just replaced the rubber balloon with a satellite in medium Earth orbit. The math is identical. The hardware got smaller and faster and the "balloon" got pushed up to 20,000 km.

The 1945 generation of surveyors lived in the brief, weird window where the technique was new enough to need a journal article and old enough that the underlying idea — "use a high-altitude radio beacon as a reference" — was already understood. They built the conceptual scaffolding that GPS engineers in the 1970s borrowed wholesale. Ryall's balloons were prototypes of the constellation we now take for granted.

The same issue, incidentally, includes an editorial "To Municipal Engineers" by Howard R. Saunders and a piece called The Engineer's Place in Civilization by Louis H. Berger — a reminder that 1945 surveyors thought of themselves not as technicians but as participants in rebuilding the postwar world. They were, it turns out, also quietly inventing the future of navigation.