The Railway Mail Service began exchanging mail “on-the-fly” in 1869. This system of mail cranes made it unnecessary for trains to stop at every town to load and unload mail. As a train approached the station’s crane, a clerk on board prepared a catcher arm to snatch the mailbag in the wink of an eye. The clerk then kicked the town’s incoming mailbag off the moving train. Experienced clerks could make the switch at night with nothing but the curves and feel of the track to give them their bearings. As good as the system was, there a few snags. Mailbags sometimes burst open on impact, sending letters flying. And clerks occasionally prepared the catcher arm too early or too late, leaving the mail dangling on the crane.