This page features horns that don't really fit any particular category
Hancock 4700 Air Whistle
The Hancock 4700 air whistle was Hancock's attempt to produce whistles for diesels after the retirement of steam locomotives. The New Haven was the biggest purchaser but the whistles fell out of favor due to their low volume
The Holden J3 was created in 1954 for use on Canadian snow plows. While blowing a similar chord to an M3H, it was designed to be of low maintenance and non-tunable
The Prime 990 was Prime Manufacturing's attempt at a locomotive air horn. It closely mimicked the sound of the Leslie RS3K. Burlington Northern was a well-known customer of Prime