Bravo Sierra would be soldier speak for the alpha digits B & S
Wikipedia explains several versions of spelling alphabets. A Soldier might spell his/her ABCs as Alpha, Bravo, Charlie, Delta. A WW II soldier would have said Able, Baker, Charlie, Dog. You might remember the old T.V. Show, Adam 12, They would have said Adam, Boy, Charles, David. These are all ways that one could send alpha letters over a poor radio connection and have some hope that the other end could make it out. Thus the use of Niner for Nine, which could be mistaken for Five. When you are sending coordinates for an artillery barrage, you want the numbers to be right on. Hopefully, I did not come across as an Adam Henry. Just trying to help the understanding.
Whiskey Tango Foxtrot, over?