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National Museum of Nuclear Science & History

Mail Censorship

History Page Type:
Wednesday, March 7, 2018
Your pen and tongue can be enemy weapons

Secrecy was of the utmost importance during the Manhattan Project. The Manhattan Project workers and their families who lived at the three primary sites (Los Alamos, NM, Oak Ridge, TN, and Hanford, WA) were told that the nature of their work was crucial to victory and the safety of the United States. It wasn’t until midway through the war that mail censorship became a staple of life for residents of the “secret cities.” This article will focus on mail censorship at Los Alamos.

Mail Censorship at Los Alamos

According to the Office of Censorship, Manhattan Project participants were forbidden to discuss: “(a) Your present location except that it is in New Mexico; (b) the names of your associates and the personnel employed on the project both military and civilian; (c) the professions of personnel employed at the project; (d) the nature or any details of your work; and (e) the number of people at the project either military or civilian.”  

The process of censorship at Los Alamos was slightly different than the censorship a soldier abroad experienced, where parts of letters were blacked out or removed from the letter. Manhattan Project workers and their families were ordered to send outgoing mail unsealed, so it could be read by the censors. Incoming mail was also censored before it was delivered. The incoming mail that was censored was still not allowed to be cut, per Project Y director J. Robert Oppenheimer’s instructions.

General Leslie Groves and Oppenheimer instituted these censorship rules at the Los Alamos laboratory in December 1943. Groves and Oppenheimer agreed that censorship would be formally instituted, but that nothing from letters received would be cut. Mail censors would send notes to recipients if there was anything that violated the secrecy of the project. Oppenheimer believed in this strongly, at times standing up for individuals who had their letters cut. For example, Bob Carter recalled Oppenheimer intervening after he received a letter from his mother that had portions cut from it.

The purpose of mandated censorship was for the secrecy of the project. Citizens were not allowed to reveal where they were living, the names of others who lived there or the work they were doing. Everyone who worked on the Project was classified as an “engineer.” The majority of mail sent to individuals who called “the Hill” their home during the war years were addressed to “PO Box 1663.” However, there were other PO boxes that received mail during this time, including 1539, 169, 1036, 527 and 180.

Many individuals who lived at Los Alamos chafed at having their letters censored. Richard Feynman (the town prankster) enjoyed pulling jokes on the censors at Los Alamos when writing letters to his wife, Arline Greenbaum, in Albuquerque. Greenbaum would send codes to Feynman for him to decipher. The censors did not find this game funny. It was agreed that the two could keep up this game if Greenbaum included a key in her letters for the censors to read first, before forwarding it along to Feynman. Feynman and his wife also moved into trickier cryptography and sent letters with whited-out words and whole passages missing.

Pat Krikorian was afraid she would lose her job when her brother, who was stationed overseas, sent letters to her claiming that he knew inside secrets about Los Alamos. After her commanding officer found out about the incident, she didn’t write to him for the duration of the war, and she received no further mail from him until the end of the war. Later she found out that her brother was friends with a soldier who had lived in the Los Alamos area before the war.

Situations like the Feynmans’ and Pat Krikorian’s demonstrated the strictness of mail censorship and the importance of keeping sites like Los Alamos secret. But mail censorship didn’t always prevent individuals from communicating with their family and friends.

Censorship was heavily documented at Los Alamos. Oak Ridge, Tennessee and Hanford, Washington—the other two “secret cities”—also experienced some forms of mail censorship. However, the censorship at these two sites is not as well documented as at Los Alamos. 

Manhattan Project billboard

A World War II security billboard at Hanford, WA

More Historical Resources:
  • Jennet Conant, 109 East Palace: Robert Oppenheimer and the Secret City of Los Alamos (New York: Simon & Schuster, 2005).

  • James Kunetka, The General and the Genius: Groves and Oppenheimer. The Unlikely Partnership that Built the Atom Bomb (New Jersey: Regnery History, 2015).