[GreenKeys] M15

[Jim Haynes]

My understanding is that it was designed to go to 75 wpm.  Or maybe was
originally designed for 60 and then was found satisfactory at 75, perhaps
with a few changes.  What I don't know is who used them at that speed.
We know AP and UPI ran them at 60 wpm.  Seems like the wire services would
most benefit from the higher speed, except maybe they still into the 1940s
had some Model 12 machines in service.  TWX stayed at 60 wpm until the
cutover to dial TWX and 8-level machines.  A.P. went so far as to convert
their machines to 50 baud - I've wondered why they didn't go to 75 wpm
instead.  So it must have been largely private services that used 75 wpm.

We know that in WW-II the military made some use of 15s running at 100 
wpm, accepting the need for increased maintenance to get the higher
traffic capacity.  I would assume that was largely on land lines within
CONUS, since we never encounter old military machines from the field
set up for 100 wpm.

Another large user of TTY equipment was the CAA/FAA and Weather Bureau,
but I believe they operated at 60 wpm until the cutover to ADIS about
1960.  By then they had pretty much phased out the 15s in favor of 28s.

In message switching systems such as 81D1 it is desirable to operate the
cross-office circuits faster than the out station circuits, and the
cross office circuits could operate at 75 wpm, but there was no need
for printers on those circuits.

So who were the 75 wpm users?

On Mon, 13 Apr 2015, Ed Sharpe Archivist for SMECC via GreenKeys wrote:

> 75 wpm is  booking along   for a  15! It has a nice  sound!
> I rather  like it.... but     I wonder what the wear  factor is..?
>