As soon as the revolving guns are available, place as many on the ships hull as possible. It makes ship to ship combat much easier. The average destroyer can hold up to five of the 57MM on deck. Do not worry about the traditional cannons, as their rate of fire is too slow. The revolving guns are very powerful and rarely run out of ammunition. The only downside is that you must be fairly close for them to be effective. Race up next to enemy ships and shoot them and they will be destroyed quickly and generally cannot fire back due to the close range. Upgrade the size/caliber of the revolving guns whenever possible in the R&D section. Once the wave guns are available, add one or two to take out entire fleets, then use the revolving guns to take out the survivors. A combination of wave gun and revolving guns can take out anything in the game.