When Was the Semaphore Arm First Used in the US?

[NW Mailing List]

I should have made my post more explicit.  My question is NOT about the introduction of Automatic Block Signals or Interlocking Home Signals of the Semaphore type on the N&W.  My question is about the semaphore ARM (blade) itself.  It's rather apparent that the first use of a semaphore arm the N&W was as a Train Order Signal... but when and where?  That's the information that seems lost to history. 

  

-- abram burnett 
 
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