The Goose Flies South

First published in Sky Fighters, Summer 1947. Reprinted in the collections Night Over The Solomons and The Collected Short Stories of Louis L'Amour - Volume 4: The Adventure Stories.
The year is likely 1946. Turk Madden is flying out of South America when he is hired to transport a small team of scientists to a private atomic bomb test being planned by Argentine militarists and ex-Nazis now living in that region. Madden's is there for more than just piloting, however, as he has his own set of orders.