Shortly before W.W.I, Transfer Clerks were assigned at some of the larger railroad junction points. These Transfer Office (TO) facilities were space exclusively used by Railway Mail Service and Postal Transportation Service clerks that were leased by railroad companies. The primary function of Transfer Clerks was to "space" all mail-carrying trains (determine the amount of mail for each car), whether it was in baggage cars or storage cars, protect the mail during transfers between trains or connecting highway routes, and supervise the loading and unloading of mail.
When Transfer Clerks were not supervising the handling of the mail at a depot, many Transfer Offices had a small letter case for clerks to distribute letters mailed at the depot letter boxes. At many locations, they provided a hand-to-hand receipt for registers between connecting Railway Post Office (RPO) routes. They also posted orders on the Chief Clerk's order books which RPO clerks were required to read before starting work.