[GreenKeys] Interesting WU film on You Tube

[Jim Haynes]

In addition to the system John mentioned, which was Plan 55 for the
Air Force, there is an awful lot of information in the Western Union
Technical Review, which is at
massis.lcs.mit.edu/archives/technical/western-union-tech-review/

The system used for domestic telegrams was Plan 21A.  The U.S. was
divided into 15 switching areas.  A one or two letter address code
at the front of a message told the destination switching area, and
sometimes in special cases a destination within the switching area.
The sending office sent the message to the switching center in its
area.  There the destination code was read and used to route the message
to the destination switching area.

At that point operators read the address information from the message
and with pushbuttons controlling rotary stepping switches routed the
message to the destination office.  The reason for this manual step was
that routing messages addressed to the general public is too complicated
for electromechanical switching to handle.  In big cities different
destination offices might serve opposite sides of a city street, for
example.  The originating offices needed to have only a few pages of
routing information covering special cases in distant switching areas
and routes for the local switching area.  At destination offices the
message addresses were read by the operators and used to route the hard
copy by delivery boys, or by telephone delivery, or by fax or
teleprinter to the customers.  A message passed through at most two
switching offices: that of the originator and that of the destination
if different from the originator.

The Bell System had an automatic switching system 81D1 that was used
for the message systems of corporate customers.  Western Union had
several systems for the same purpose, generally Plan numbers 51 and up.
Plan 51 was a system using manual routing through rotary stepping
switches controlled by pushbuttons.  Plan 55 was a fully automatic
system for the Air Force, and as John noted used six-character routing
codes and fully automatic routing.  (Since the destinations were all
communications offices on Air Force bases; it was up to the destination
offices to send the hard copy messages to the end recipients.)  Typical
of the U.S. military, the AF had W.U. Plan 55, the Navy had a Bell System
switching system 82B1, and the Army had a military nomenclatured system
made by Kleinschmidt and Automatic Electric, AN/FGC-30.  These systems
were more or less inter-operable since the message routing codes were
uniform across the services.

I believe the last major W.U. system was Plan 59 made for the FAA in
Hawaii.  It really pushed the limit of what could be done without
resort to computer technology.