I was able to blow up the bridge by placing all 5 of them at the base of the bridge just under it.
BTW when you are getting out that section of town after blowing the bridge, you are told that there is a boat near bridge number 3.
I went that way but didn't see any boat. I did hear something above me, so I looked up into the sky and saw a T-72 falling from a great distance. I was stunned at the site of it. The tank landed on the other side of the river and it's surviving crew member bailed out and started shooting at me. I gunned him down and swam over to the tank. There was not a scratch on it and it was close enough to the shore that I could get in and drive away. LOL!