World War II brought hard times for the Library. Assuming an attack was imminent, antiaircraft guns were installed on rooftops and staff conducted 24-hour air raid watches from Library buildings. After the bombing of Pearl Harbor, staff packed up Library treasures and shipped them to safe locations.

Included in these treasures were 24 of poet Walt Whitman's personal notebooks. The notebooks, an invaluable resource on Whitman's early career, contain early versions of poems that appeared in Leaves of Grass, his major work, and notes from his time as a volunteer nurse during the Civil War. When the evacuated materials were returned in 1944, however, 10 of the notebooks were missing. Library officials called on the FBI to help find the missing notebooks, but they remained elusive for more than 50 years.

In 1995, four of the 10 notebooks appeared at Sotheby's in New York and were returned to the Library. Although saved from the air attack that never happened, the notebooks required preservation treatment once they returned. The Library soon embarked on a dual mission of preserving the fragile originals while making them accessible for worldwide research.