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Railway Mail Crane

a mail clerk leans out of a train
Clerks worked hard to sort and prepare mail for each stop along the way.

Mail crane on display at the National Postal Museum
Mail crane on display at the National Postal Museum

Railway Mail Service revolutionized the way mail was processed by sorting mail aboard moving trains. A critical component of the service was the mail exchange made between moving trains and small towns. This tricky and potentially deadly component, known as “mail on–the–fly,” allowed mail to be exchanged between Railway Post Office (RPO) cars and towns too small to rate trains stops.

These mail exchanges began in the mid 1860s. At first engineers slowed trains to a crawl so clerks could exchange the mail by hand. This inefficient system was replaced by track side cranes on which postmasters suspended mail pouches ready for pickup. 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. Standing at an average of just over ten feet in height, these iron cranes were common slights along U.S. railway lines.

As the train approached, a RPO clerk prepared the catcher arm, which would then snatch the incoming mail pouch in the blink of an eye. The iron arms of the crane would pop open, releasing the pouch to the RPO car. At the same time, the clerk kicked the outgoing pouch out of the car. The special catcher pouches used in the service had metal rings at each end to attach to mail cranes.

A successful on–the–fly exchange depended on many factors, including the clerks’ experience, strong mail pouches that would not burst open when snatched by a fast-moving iron crane or kicked off a moving train, postmasters who attached the pouches correctly and well maintained equipment that worked as expected.

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. Not all swaps ended well. A clerk who did not pay sufficient attention to the job ran the risk of being struck and killed.

 Short, silent film demonstrating how "mail on–the–fly" worked. The original film is in the collection of the Library of Congress.

Retrieving mail from the crane was only one half of the job. As many clerks learned, kicking the mail pouch out could be just as difficult. One clerk booted an outgoing pouch with so much force that he sent it flying through the railroad terminal window. The clerk who did not kick hard enough watched helplessly as the pouch was sucked under the train and mail torn to shreds by the train’s wheels. Clerks had a name for that. They called it a snowstorm. 

Filmed in 1993, this is the story of the Railway Post Office clerks, as told by four ex RPO clerks, Tom Clifton, Harold Coffman, Winston Lark and Don Shenefelt.

By the 1870s, on–the–fly exchanges helped position Railway Mail Service as the backbone of the nation’s postal system where it remained into the 1930s. The service began a steady decline in the late 1940s as airline and automobile passenger traffic grew. By 1948 there were only 794 RPO lines still in operation. In 1962, the number was down to 262.  By 1971, only thirty trains were still using railway mail cranes in the United States. On May 1 of that year, AMTRAK (America, travel, and track) began operations and after just over a century of service, on–the–fly mail exchanges came to an end.


Long, Bryant Alden. Mail by Rail, New York: Simmons-Boardman Publishing Corporation, 1951.

Romanski, Fred J. “The Fast Mail: A History of the U.S. Railway Mail Service,”Prologue Magazine, Fall 2005, Volume 37, #3, Library of Congress, Washington, DC.

Culbreth, Ken. The Railway Mail Clerk and the Highway Office, Trafford Publishing, 2007


Railway Mail Service, National Postal Museum online exhibit

The Railway Mail Service Library

Written by Nancy A. Pope
December 2007