Brazil was still formally neutral when President Getúlio Vargas signed a defence agreement in July 1941 that let the United States build air bases along the country's north and northeast coast. On 2 March 1942 Vargas created Natal Air Force Base — BANT — by converting a former French airfield outside the city. The Americans then built their own installation, Parnamirim Field, immediately to the east, at a cost of $9.5 million. Brazil declared war on Germany and Italy on 22 August 1942, and what had been a hedge became a front-line asset. The US Department of War rated Natal among the four most strategically important points on earth, alongside the Suez Canal, the Bosporus and the Strait of Gibraltar.

Roughly six thousand workers built Parnamirim Field, and most of them came from the dry interior of Rio Grande do Norte — people from a countryside that drought regularly emptied, walking toward wages on a coast suddenly full of them. They were not passing through. They put up a settlement west of the two bases and stayed, and that camp outlived the war it was built for: it became a district in 1948 and the municipality of Parnamirim in 1958, a city that exists because of an airfield. The same labour laid a twenty-kilometre paved road from the bases down to the Port of Natal, replacing the dirt track that had served before.

Once the South Atlantic ferry route opened, the wing responsible for it moved its headquarters to Parnamirim Field, and the traffic promptly outran the facilities. Through 1942, aircraft, materiel and mail piled up at Natal faster than they could be flown onward across the ocean. Between 1943 and 1945 the field ran as a genuinely joint operation — the Brazilian Air Force, the United States Army and Navy, the Royal Air Force and commercial airlines all sharing the same runways, with American units handling maintenance and security. How many aircraft crossed from here has been inflated in the retelling often enough that the honest answer is simply: a great many, continuously, for three years.

The USS Humboldt tied up at the Port of Natal on 28 January 1943 carrying Franklin Roosevelt, on his way home from the Casablanca Conference. Getúlio Vargas came to meet him. What the two presidents worked out on the Potengi river — the Potengi Conference, as Brazilians call it — was the shape of Brazil's active participation in the war, and it led directly to the Brazilian Expeditionary Force, which shipped for Italy in July 1944. The city itself was transformed by proximity. Natal held 54,836 people in 1940 and 103,215 by 1950, nearly doubling in a decade, and the dances and social gatherings that grew up around the foreign garrisons left American music behind in the local repertoire.

In October 1946, a little over a year after the war ended, the United States handed Parnamirim Field to the Brazilian Air Force. It has been Brazilian ever since, and today the installation is Natal Air Force Base, Ala 10. Six squadrons work from it: 1º/5ºGAv "Rumba" and the 2ºETA "Pastor" transport unit flying C-95 Bandeirantes alongside C-97 Brasílias and C-98 Caravans, 2º/5ºGAv "Joker" with A-29A Super Tucanos, 1º/8ºGAv "Falcão" with H-36 Caracal helicopters, 1º/11ºGAv "Gavião" with H-50 Esquilos, and 3º/1ºGCC "Morcego", which runs air-defence radars rather than aircraft. Its own record carries losses as well: on 3 July 1977 a C-95 Bandeirante crashed shortly after taking off from Natal, and all eighteen people aboard died.

For decades the base shared its concrete with Augusto Severo International Airport, the civil terminal that handled Natal's airline traffic. That ended on 31 May 2014, when scheduled flights moved to a new airport built inland at São Gonçalo do Amarante and the military got its field back to itself. Three asphalt runways remain in service — the longest at 2,600 metres — on ground fifty-one metres above the sea, eighteen kilometres from downtown Natal. Super Tucanos and Caracals now use pavement laid so that four-engined transports could reach Africa. Very little of the wartime story is signposted, but the geometry has not changed: turn east off the end of the runway and the next land is Africa.