Styleone: Yes, from memory it was something like this:
1. There is only one cannon per player in a game.
2. Can fire a shot two spaces in front of it, e.g. if it is on e5 it can only shoot at e7.
3. It may fire at and kill any piece, even undetected, but it cannot take out mines nor the hq.
4. Any piece may capture it. Also, if it moves onto a space occupied by the enemy, it will lose.
5. The shot is considered as a move, so you cannot move it and fire on the same move.
6. In small espionage, the board can accommodate another piece, but in open espionage, it would have to replace one of the existing pieces, perhaps a 1?
That's about it!