a pouch of mail ready to be dispatched as the train passed the station. In a co-ordinated movement, the catcher arm was swung out to catch the hanging mail pouch while the clerk stood in the open doorway. The mail pouch had a strap around the middle, and the strap was tightened in preparation for pickup with an approximately equivalent weight of mail in either end of the pouch to prevent the heavier end from pulling the lighter end off the catcher arm. As the inbound pouch slammed into the catcher arm, the clerk kicked the outbound mail pouch out of the car, making certain to kick it far enough that it was not sucked back under the train. Outbound pouches of first class mail were sealed with a locked strap for security. Larger sacks with optional provisions for locking were used for newspapers, magazines, and parcel post. An employee of the local post office would retrieve the pouches and sacks and deliver them to the post office. In the 1950s the Budd Company offered two versions of its self-propelled diesel RDC with RPO: the RDC-3 combine and the RDC-4 (a baggage/mail/express only unit). These models were purchased by the New York Central, Boston & Maine, New Haven Railroad, Rock Island, Pacific Great Eastern, Northern Pacific, Canadian Pacific Railway, Canadian National and Minneapolis & St. Louis. Cancellation stamps Most RPO cars had a mail slot on the side of the car, so that mail could actually be deposited in the car, much like using the corner mail box, while the train was stopped at a station. Those desiring the fastest delivery would bring their letters to the train station for dispatch on the RPO, knowing that overnight delivery would be virtually assured. The mail handled in this manner received a cancellation just as if it had been mailed at a local post office, with the cancel giving the train number, endpoint cities of the RPO route, the date, and RMS Railway Mail Service or PTS Postal Transportation Service between the killer bars. Collecting such cancellations is a pastime of many philatelists and postal history researchers. The Railway Mail Service organization within the Post Office Department existed between 1864 and September 30, 1948. It was renamed the Postal Transportation Service on October 1, 1948, and existed until 1960. After 1960, the management of railway post office routes as well as Highway