The Postal Transportation Service (PTS) was the renamed successor to the Railway Mail Service of the United States Post Office Department from 1 October 1949. Although this branch of the service had been in charge of all transit mail, some parts had little to do with railroads, even though they were still the most important part of the service. In 1950, of the 32,000 clerks assigned to the PTS, only about 16,000 actually worked on trains. The remainder were in terminals, transfer offices, Air Mail Facility, Highway Post Offices (HPO), administrative offices, etc. Boat Railway Post Office (Boat RPO), Streetcar Railway Post Offices, and the Seapost Service had already been discontinued. The name of the Chief Clerk's office was changed to District Superintendent's office.