Frank Walker served as Postmaster General from 1940 to 1945. The records from his post office tenure include correspondence, memoranda, notes, minutes of the Post Office Wartime Operations Board, reports on topics relating to the postal service, reports from postal inspectors, files on job seekers, and copies of speeches given by Walker. Much of Walker's time as Postmaster General was spent working on the problems of delivering mail to servicemen overseas while operating the domestic postal service during World War II. His correspondence, many of the reports filed in this series, and the minutes of the Post Office Wartime Operations Board discuss wartime concerns such as domestic shortages, censorship of mail, and the logistics of transporting mail overseas.

While he was Postmaster General, Walker maintained two offices, one in New York for his personal business and the other in Washington for his official records. In practice many of his letters that were unrelated to the postal service, such as correspondence concerning the Democratic Party and the Walker family business, were filed with the records of his Washington office. For this reason Walker's Post Office correspondence, which deals with all aspects of his work as Postmaster General, has been kept as part of the general Correspondence Series in boxes 24 to 44. The correspondence that has remained in the Post Office Series is filed by subjects such as job applications, specific reports, special issue stamps, or speeches given by Walker. The memoranda files in this series also contain some correspondence along with memoranda from his office staff and other government agencies.

Of special interest in this series are copies of speeches given by Walker while he was Postmaster General, beginning in the summer of 1941 with a speech on isolationism and continuing on with speeches on the war effort. Along with drafts and final versions of the speeches, Walker also kept files of letters written in reaction to them. Most of the speeches given by Walker can be found in the Speeches Series, while newspaper clippings on his work with the Post Office are in the Srapbook Series.