This would clear the highway:

[Are_grits_groceries]

http://www.youtube.com/watch?v=cNo99KcqGbQ

This is a 1940's Doran Cunningham air horn. Usually found on WWII US Navy destroyer ships, and also found on some older ferries. There are only 2 of these that are being used that I know of. Mine and Adam's (Airraidsiren on YouTube). Very rare that only six have been seen in pictures and each one had a different configuration. The 6B is close to 200lbs. of brass, has a 12" diaphragm,my 6B measures 36 1/4" long, and has an 18" bell/horn opening.
There are markings at the footing of the air inlet "DD416". This is not the biggest horn made; but is considered the best because of it's sound!
http://www.neatorama.com/

Whooooooooooooosh!

[MineralMan]

1. Not bad...not bad at all.

There are louder horns, though.

[MineralMan]

2. More details...

Diaphone driven horns are louder than this horn, by a great amount. The largest Type G diaphones, only a couple of which exist any longer, can be heard for at least 20 miles.

Still this one's pretty good for a vehicle-mounted horn.

Google Diaphone horn if you want more info...

[bluedigger]

3. That's a great horn!

Were you aware that DD416 is a destroyer reference? DD416 is the USS Walke, which was sunk with heavy losses in the second battle of Guadalcanal. http://en.wikipedia.org/wiki/USS_Walke_(DD-416)

pics here: http://www.destroyerhistory.org/goldplater/usswalke.html

From wiki: "Walke began an overhaul at the Boston Navy Yard on 25 November 1941 and completed it on 7 December 1941, the "day of infamy" on which Japan attacked Pearl Harbor and thrust the United States into war in the Pacific. Departing the yard on that day, Walke reached Norfolk on 12 December, via Casco Bay, and remained there until 16 December when she sailed for the Panama Canal and the Pacific."

Do you suppose your horn was destined for the Walke's refit, and they left without it on the Day of Infamy? Dec. 7 was a Sunday, after all, an unlikely day to coincidentally finish an overhaul.