What's the history of the 21 GUN SALUTE?

As far as I know, it's seven gunners, three shots, right? What is the significance of these numbers?
Update: Yes, Alpha, I could. But then you'd have two less points, wouldn't ya?
Update 2: Thanks, Kheelan. I had, indeed, confused the two. It was the three shot volley that I was curious about.
6 answers 6