Most of what we know about them is on the name plate.
Without actually seeing inside it, many people believe that it's a dual toned model, housing a rotor/stator assembly in the base of the front projector, and one in the rear chamber that has the hook-shaped horn coming off it.
You can't see it there, but the front is actually a horn within a horn. The way I think it works (I'm not passing this off as a solid fact yet) is this:
Air enters through the central horn and sound is dispersed through the space between the inner and outer horns. On the back, air would come in through the little protrusion on the back and exit through the hook-shaped horn.
Here's a photo showing the front of this siren, with the coaxial horn arrangement:
http://winnipeg.urbex.ca/Ogilive/46.jpg
You can also see one of these in the movie, "Blues Brothers," but it has been butchered by Hollywood to be a giant megaphone. An electronic horn has been placed inside it, and the rear horn has been blocked off.