In 1942, the United States began a top secret endeavor known as the Manhattan Project. Engineers of the United States army set up in the small town of Los Alamos, New Mexico, and the town's post office was an important part of the project.

Constructed in 1920, the building operated as both a school and post office for Los Alamos and surrounding towns. Locals petitioned to update the name for accuracy to Los Alamos Post Office in 1941. Shortly thereafter, the Manhattan Project moved in to plan and produce the first atomic bombs during World War II.

The location was known as Project Y. Theoretical physicist J. Robert Oppenheimer headed the Manhattan Project and liked the location of Los Alamos, he said his team could be inspired by the natural beauty.

Mail was not delivered to the Los Alamos Post Office for the duration of the project due to strict secrecy. Military police carried the mail into secret mail drops from Los Angeles and Santa Fe. Government officials eventually allotted three post office box numbers to Los Alamos. Local hospitals used these box numbers as the “place of birth” on the birth certificates of all children born during the four-year project.

The military laboratory of Los Alamos evolved into a civilian and scientific community. The post office, once the center of atomic bomb development, now simply provides postal services to the citizens of Los Alamos.