By nature, code names and cover stories are meant to give no indication of the secrets concealed. “Magic” was the name for intelligence gleaned from Japanese ciphers in World War II, and “Overlord” stood for the Allied plan to invade Europe.

Many people assume that the same holds true for the Manhattan Project, in which thousands of experts gathered in the mountains of New Mexico to make the world’s first atom bomb.

Robert S. Norris, a historian of the atomic age, wants to shatter that myth.

In “The Manhattan Project” (Black Dog & Leventhal), published last month, Dr. Norris writes about the Manhattan Project’s Manhattan locations. He says the borough had at least 10 sites, all but one still standing. They include warehouses that held uranium, laboratories that split the atom, and the project’s first headquarters — a skyscraper hidden in plain sight right across from City Hall.

“It was supersecret,” Dr. Norris said in an interview. “At least 5,000 people were coming and going to work, knowing only enough to get the job done.”