For 17 months, from 1935 to 1937, Nazi explorers under the guidance of Mr. Schulz-Kampfhenkel hacked through forests around Brazil’s border with French Guiana. They collected animal skulls and indigenous jewelry, and they studied the topography along the Jari River, a 491-mile tributary of the Amazon.

“The expedition started out with the usual scientific pretensions,” said Jens Glüsing, a longtime correspondent in Brazil for the German magazine Der Spiegel who wrote a book about the Guyana Project. “But back in Germany, as the war started, Schulz-Kampfhenkel seized on this idea for Nazi colonial expansion.”

Mr. Schulz-Kampfhenkel presented his plan in 1940 to Heinrich Himmler, the chief of the SS and the Gestapo. It envisioned the endeavor as a way to blunt the regional sway of the United States by seizing control of French Guiana and the neighboring Dutch and British colonies (now the independent nations of Suriname and Guyana).

But the dream of forging a German Guiana fizzled. Perhaps it was because French Guiana had already fallen into the friendly hands of the collaborationist Vichy regime.

Or maybe it had to do with the ill-fated Jari expedition itself.

The expedition had a Heinkel He 72 Seekadett seaplane, which was promoted as an example of Nazi industrial innovation. But the aircraft capsized after hitting driftwood a few weeks into the expedition.