Cleveland Press reporter John Raper took a vacation in New Mexico in 1944 and came back with a sensational story — he had discovered a “mystery city” there, a closely policed community at work on some top-secret project northwest of Santa Fe.

Uncle Sam has placed this in charge of two men. The man who commands the soldiers, who sees that the garbage and rubbish are collected, the streets kept up, the electric light plan and the waterworks functioning and all other metropolitan work operating smoothly is a Col. Somebody. I don’t know his name, but it isn’t so important because the Mr. Big of the city is a college professor, Dr. J. Robert Oppenheimer, called ‘the Second Einstein’ by the newspapers of the west coast. …

It is the work of Prof. Oppenheimer and the hundreds of men and women in his laboratories and shops that makes Los Alamos such a carefully guarded city. All the residents will be obliged to remain there for the duration and for six months thereafter and it seems quite probable that many of them don’t know much more about what is being done than you do.

Apparently Raper had driven into the compound to investigate but was escorted closely and allowed to see nothing. He told curious New Mexicans, “I don’t know a bit more about it than I did before I went.” Santa Fe residents whispered that Oppenheimer was building some sort of chemical weapon, an explosive, or “a beam that will cause the motors to stop so that German planes will drop from the skies as though they were paving blocks.” But all of this appeared to be rumor.

Raper published his story in the newspaper on March 13. It provoked an immediate stir among the Manhattan Project authorities, who quashed a followup story in TIME and briefly considered having Raper drafted into the Pacific Theater. But ultimately nothing came of it, and no Axis spy seems to have pursued it. American Institute of Physics science historian Alex Wellerstein discusses the story, and provides the full text with its lurid illustrations, on his Restricted Data blog.

(Thanks, Larry.)