Manhattan Project

American  

noun

1. U.S. History. the unofficial designation for the U.S. War Department's secret program, organized in 1942, to explore the isolation of radioactive isotopes and the production of an atomic bomb: initial research was conducted at Columbia University in Manhattan.

---

Manhattan Project British  

noun

1. (during World War II) the code name for the secret US project set up in 1942 to develop an atomic bomb

---

Manhattan Project Cultural  

1. The code name for the effort to develop atomic bombs (see also atomic bomb) for the United States during World War II. The first controlled nuclear reaction took place in Chicago in 1942, and by 1945, bombs had been manufactured that used this chain reaction to produce great explosive force. The project was carried out in enormous secrecy. After a test explosion in July 1945, the United States dropped atomic bombs on the Japanese cities of Hiroshima (see also Hiroshima) and Nagasaki.

---

Etymology

Origin of Manhattan Project

Extracted from U.S. Army Corps of Engineers Manhattan District and DSM (Development of Substitute Materials) Project

Example Sentences

Historically, Los Alamos served as the top-secret heart of the Manhattan Project, where the first atomic bombs were designed and built on an expedited timeline.

From Barron's • Apr. 23, 2026

"It's like if the Manhattan Project announced the nuclear bomb within a cute little Calvin and Hobbes cartoon."

From Barron's • Apr. 10, 2026

Many members believe they’ve lost loved ones to radiation, or were themselves likely impacted by early-life exposure as children of Manhattan Project engineers.

From Los Angeles Times • Mar. 27, 2026

During World War II, Vannevar Bush ran the Office of Scientific Research and Development, which funded research for radar, guided missiles and even the Manhattan Project.

From The Wall Street Journal • Oct. 19, 2025

Just two years before, Stimson had decided Truman wasn’t important enough to know about the Manhattan Project.

From "Bomb" by Steve Sheinkin