The Leslie S5T was once a commonly used horn on U.S Class 1 railroads, but it has become very rare.
Like the Nathan K5LA, there are many different variants in which the "bells" on the horn set are arranged. Such as: S-5T-RRO, S-5T-RF, S-5T-RO, etc.
Several Australian railroads have actually used the S5T on some of their locomotives.
Very few small Canadian Shortlines (Class 2 and 3 railroads) have used the S5T on some of their locomotives as well.
Some Early S5T’s were fitted with 277 bells instead of 25 bells, Making them sound similar to The S5D.
Before the S5T’s introduction in 1952, there were the rare Leslie S-5A and S-5D. The S-5D sounded similar to a Nathan M5. And the S5A played a B Major 7th Chord.
http://www.youtube.com/watch?v=JUvT1wvZVZ4&feature=fvst YouTube Video sound example
http://atsf.railfan.net/airhorns/s5t.html History examples
https://www.youtube.com/watch?v=g5qKeGV3CTo (Early S5T)