I saw somewhere along time ago these guys were making model boats. Battle ships and the like.
The hulls were built out of soft woods, balsa and basswood for the most part. The rules of construction were pretty explicit.
Anyhow inside the hulls they placed RC controls in a water tight box, electic motors, and fitted 'cannons' that shot BB's using compressed air. You were limited to the number of BB's the boat could carry but not the number of guns.
So the idea was to shoot the other guys boat with the bb cannons and punch holes in the soft wood hulls. The construction paramaters ensured that the boat would sink if holed. There was a minium weight per class of boat which usually required the addittion of lead ballast.
last one still floating won
looks like they are still around
http://www.modelwarshipcombat.com/
pictures and videos here
http://www.modelwarshipcombat.com/pictures.shtml