Originally Posted by
cudak888
A non-muffled Nathan K5LA or Leslie S3L air horn is a force to be reckoned with. Takes a bit to get used to, though it isn't startling if you've been around railroads for a while.
-Kurt
P.S.:
http://en.wikipedia.org/wiki/Train_horn
Ship horns FTW.
http://www.shiphorns.com/media/
(personal favorite clip: Cunningham Air Whistle 6B, seventh from the bottom on the left side with an animated gif preview)