Railway Mail Service crane with pouch
Slightly over ten feet tall, these iron cranes were common slights along U.S. railway lines from the late nineteenth century through the twentieth. They were placed near train tracks in order to allow Railroad Post Office (RPO) cars to exchange mail without stopping. Instead of stopping at every small town to receive or pick up mail, RPO cars were fitted with catcher arms that snatched mailbags off cranes such as this.
As the train approached, a clerk prepared the catcher arm, which would then snatch the incoming mailbag in the blink of an eye. The iron arms of the crane would pop open, releasing the bag to the RPO car. An RPO clerk then booted the outgoing mail out of the train near the crane. Experienced clerks spoke with pride of making the switch at night with nothing but the curves and feel of the track to warn them of an upcoming catch. This mail-exchange process was known as 'mail on-the-fly'.
Mail was exchanged on nonstop trains as early as 1865 without the cranes. To do so, engineers slowed trains to a crawl so clerks could exchange the mail by hand. Officials soon scrapped the inefficient and dangerous system. The first trackside Railway Mail Service cranes were wooden, F-shaped mechanisms. They were soon replaced by a simple but more durable steel hook and crane.
As tremendously successful as it was, mail on-the-fly suffered its share of glitches. Clerks had to pay special attention to raising the train's catcher arm. If they hoisted it too soon, they risked hitting switch targets, telegraph poles, or semaphores, all of which would rip the catcher arm right off the train. Too late, they would miss an exchange. Each missed exchange netted a clerk five demerits.
Missed exchanges were a special threat on a handful of eastern runs that had less than a minute between some exchanges. On single-line tracks, mail cranes could appear on either side, and woe be to the new clerk who, alertly looking out the right-hand side of the train, missed a series of mail cranes on the left-hand side. Experienced clerks on board night mail trains relied on the sound or 'feel' of the tracks, knowing by the train's speed or the curves of the track how far away they were from a mail crane.
Mail on-the-fly exchanges ended on May 1, 1971, when AMTRAK began operations. Just prior to the end of the service, thirty RPO trains still made mail exchanges on-the-fly across the country.