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.
When the S5T was first introduced in 1952. before that were the rare Leslie S-5A and S-5D, the S-5D sounded similar to a Nathan M5.
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)