Train Annunciators on the MC/NYC and C&O...
A train annunciator was a trackside device which was activated when a train entered a short track circuit at a specific location. When the device was activated, it opened a microphone on the dispatcher telephone circuit so that the dispatcher could hear the train go by the location. Another way the device worked was to start a device which would broadcast morse code letters (for the station) on the dispatcher telephone circuit. The morse code letters would repeat until the train passed out of the circuit.
Using an encoder, the dispatcher could turn off the microphone, or the Morse code repeater (but they would need to turn it back on to hear the next train). Often, they let them play.
The device let the dispatcher know when a train was passing the location of an unmanned station. This helped coordinate the progress of trains on the division. These devices were likely used as early as the 1920's and into the 1970's when telephone dispatch circuits were removed in favor of CTC operations, regular telephones and railroad radio.
There was a discussion on the MichiganRailroads.com history bulletin board about this topic in 2017.
A. G. Hudley wrote, "A tower operator of many years experience that worked for NYC/PC/CR in the Detroit area tells me that there were several train annunciators located on the Detroit to Jackson and Detroit to Toledo branches. Some of them were located around yards and stations where trains would set for a while, while they made setouts and pickups. They would beep out in Morse code letters such as that used for towers, like "FN" in Trenton. They could be turned off and back on by the train dispatcher via the same selector-set buttons that were used to ring the operators in the towers. Of course, if a train dispatcher turned one of those off, he'd have to remember to turn them back on again, or he wouldn't get an OS from the next train to pass there! We called these annunciators 'OS's".
"It was really interesting to see how these worked when a signal maintainer showed me one of these. A train passing over a short track circuit section would actuate a small sealed unit located in a wooden booth. The sealed unit contained a miniature cam shaft, which would rotate. The cams on the shaft depressed small buttons that "beeped" out the code. The Bay City and Mackinaw branches had open-air mics for annunciators."
Noted rail historian Don Meints noted that while working BO tower, Nichols tower and Pearl Street tower, he remembered these OS's very well. "We depended on them to be able to move yard engines without delaying road trains, and also, occasionally to slip an eastbound freight train through the Kalamazoo depot before a westbound passenger train.
"I can’t speak for the Toledo Branch or the West Division, but I know they were in use between Detroit and Niles. My general understanding is that they were most often placed for use with “head in” signals mounted on automatic block signals to instruct an approaching freight train to “take siding” at the next passing track or for a passenger train to call the dispatcher for instructions. The head-in signals were turned on and off by the train dispatcher by his selector buttons. They were a very helpful device to move trains, especially during night hours when there were few operators on duty to report movements.
"The OS signals were on the track circuit approaching the signal with the “head in” signal. As long as a train was on this circuit, the OS sounded. Between Jackson and Niles, to my memory, the OS signals were at Parma (westbound only), Albion (eastbound only), Marshall (both directions), Rumley Yard (eastbound only), Augusta (both), Botsford (westbound only), Miller (both), Lawton (both), Glenwood (both), and Dowagiac (both). Augusta westbound had a westbound OS approaching the siding and another leaving the coal chutes. I used to remember what morse was sent for each, but memory fails me except for Augusta (eastbound was GSE, westbound was GS, and leaving coal chutes GSW) and Botsford (BO).
"The OS's were an unusual device, and I never heard of them installed anywhere except on the MC main line.
"The open phones were in use on the Saginaw Branch at Underwood and Chesaning, and on the Mackinaw Branch at Sterling, Hodgeman, Beaver Lake, Horrigan, Vanderbilt, and Wolverine. The dispatcher could turn on and turn off the phones by his selectors I can’t speak to the Bay City Branch and I don’t remember that the Grand Rapids Branch had any.
Bill W noted that Parma also had an "open phone", at least from when he hired out in 1970 until they moved the dispatchers from Jackson to Dearborn. He said he "had a few dispatchers who would turn that phone on and then key it through the radio when you went through Parma when they were bored.
Doug Hefty, a retired C&O dispatcher noted that they had the open mic annunciator on the C&O on lines that he dispatched. "They were located at Greenville, Breckenridge, Paines and Yale. We could ring them on and off in the same manner you describe, just like ringing a depot or tower. On the train sheet, we would record the time in parentheses because we could not use them as official OS's to verify a train was complete by any of these points as far as manual block information or issuing train order or track car authority. They were considered "information only."
A.G. Hudley followed up, noting that OS annunciators on the NYC line between Detroit and Ann Arbor were as follows: No. 1 track WB -- Willow Run Yard (or Denton) - WR (came on at Denton Rd., formerly Denton station); No. 2 track EB -- Ann Arbor - A (came on west of West Ann Arbor); Willow Run Yard - WRE (came on west of Wiard Rd.). ("If there were OSs between Ann Arbor and Jackson, I didn't pay attention to them"). OS annunciators on the Toledo Branch were on the No. 1 track SB -- Wyandotte - W (came on south of the Ecorse Creek); Rockwood - R; Sandy Creek (north of Warner Yard, Monroe) - SC; LaSalle - L. No. 2 track NB had Monroe - M, and Rockwood - RN.
He noted that the OS's were all gone by 1988 when the train dispatchers moved into the Dearborn regional headquarters and all of the track circuits for these lines displayed on CRTs by computers. "I recall that while working at FN the operator had to line up southbound trains immediately when the Wyandotte OS came on, or the train would get sour signals and lay back, coming down to FN at an absolute crawl. Funny how one remembers these things after 30 years or more!".
MichiganRailroads.com editor Dale Berry had a couple of additional comments about the annunciators which he listened to at Town Line when visiting as a kid in the early 1960's. "On the Jackson east dispatcher line, it wasn't unusual for 2 or 3 code annunciators to go off at the same time for several minutes. Each one had a slightly different tone (frequency) and of course different call letters. But it could get noisy. The dispatchers and operators talked over the top of them when necessary.
"Because the annunciators actually used a motor to turn the code generator, they sometimes started slowly with a low tone (in cold weather), and then sped up and got higher and faster before getting to normal speed when they warmed up.
Dale noted that dispatchers today sit at computers and handle hundreds of miles of rail line by themselves. Fifty years ago, dispatchers and dozens of tower/block operators controlled trains using long distance open telephone lines, train orders, OS reports, annunciators, take siding indicators, and many other devices.
"I remember that whenever the dispatcher selected/rang a tower, or turned on/off an annunciator or a take siding signal, they punched a device which put out a coded signal to receivers along the dispatcher's telephone line. In every tower, each time a code was sent you could hear the ticking as each receiver decided the number of pulses sent. But the decoder would only ring if it was the number for your tower.
"At Town Line, which was a division point between the Detroit Terminal yard dispatcher and the Michigan Division Jackson East dispatcher, there were decoders for both dispatcher lines which could make the tower noisy at times."