I'm trying to determine what horns the USATC RSD1s were shipped with. Any horn gurus out there have a good guess? Best I can come up with is possible Leslie A200 or A125 or possibly Wabco E2 I think. I have no clue on the pitch.

I've just gone through all my RSD1 photos, and none of them are of help. The horns tended to be hidden from view in any ground-level photos.

From what I can tell, the ones shipped to Iran had their single horns mounted under the rim of the cab roof on the long-hood side of the cab, and that they were quite small by American rail standards.

I forgot about "The Diesel that was Drafted" in Trains magazine, from back in the days when I would read every word of the issue, several times. https://utahrails.net/pdf/Alco-RSD-1_Tr ... l-1980.pdf It looks like a single chime (bell I think they are called) horn like a Wabco E2, as you noted. Judging by the utube videos a Wabco E2 was not particularly loud but was a hooter-style sound. https://www.youtube.com/watch?v=hc9ssCxcUmA

From the photo on page 26 - it looks like a long bell Wabco AA (aka an A-2), which were common on Alco switchers.

http://atsf.railfan.net/airhorns/a2.html

I'll have to get on the hood and look at the original brackets as they still exist and whether the air line was bottom or rear feed. Yes, the horn was mounted under the overhang. Somewhere along the way the overhang was drilled to mount a horn. One of our members mounted a Typhon on the roof overhang for the time being. It's a bit floppy up there with no reinforcement. He said there's a bracket on both ends of the cab for whatever the original horn or horns were. When we inherited it, it had a Hancock air whistle on the roof.