In her new book Little Blue Dot: How GPS Shaped the Modern World, Katherine Dunn traces how GPS evolved from military technology into a daily necessity. In this excerpt at The Walrus, Dunn recounts when Todd Humphreys, a satellite navigation researcher, built a GPS spoofer in his Bay Area apartment—and watched his iPhone’s blue dot “race off down his street.” That experiment eventually led Humphreys to a bigger test at sea: spoofing an $80 million superyacht on the Mediterranean.

Any kind of interference with the spectrum is strictly illegal in most countries, but they would be doing the spoofing on international waters, at low power and at a safe distance from other boats and land. (His previous experiments had been officially sanctioned or else, like the iPhone spoofing, so low-powered they were confined to Humphrey’s apartment.) The yacht’s navigational equipment was pretty “vanilla,” Schofield assured him, a representative sample of the sort of equipment used across the industry.

The White Rose steadily made its way east from Monaco and down to the Tuscan coast. There, in international waters near a picture-perfect island of medieval houses fronted by turquoise waters, Schofield made his announcement: it was time.

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Cheri has been an editor at Longreads since 2014.