The Overcharge cannon (colloquially known as the OC) is one of the most powerful direct fire weapons ever. It is mounted on all ACUs and can be mounted on the Seraphim sACU. It drains a large amount of power (5000 units) to basically Super-charge the ACUs main gun, causing it to fire a shot that deals 12,000 damage to its target. The Overcharge cannon is effective on land and surface naval units, and also does full damage to shields. It cannot be used on air units or submersibles. This weapon can take out many non-experimental land units and will deal heavy damage to experimentals. Also, this weapon has a decent area of effect, so it can take out clusters of attacking enemy units. However, the Overcharge Cannon has a mandatory cooldown period of approximately three seconds, and cannot be fired during that time.
Please note that, for balance purposes, the Overcharge cannon's damage is severly limited against other Command units and buildings. Against other ACUs and sACUs the overcharge shot inflicts only 100 damage (the same as a normal ACU shot) while against buildings it is restricted to 500 damage.
However, the use of overcharge against an enemy commander cannot be overstated, especially in ranked games. There are many instances of games where the winner is determined by a battle between opposing commanders. Remembering that an enemy ACU causes 4000 damage to anything caught in its explosion, your goal is to kill your opponent's ACU before your ACU reaches 4000 or less HP, or else your ACU dies with it. Your overcharge cannon, which adds 100 damage to the opposing ACU everytime you use it, may be the determing factor as to whether you win the game, or end it in a draw.
Keeping in mind that an overcharge cannon destroys most units and has an area of effect, it is important to have enough energy so that you can use it the moment three seconds pass. From the start, an energy storage can help meet the 5000 unit mark. If you have a small energy-producing count, say, 50+ or so, your overcharge cannon will take longer to charge up. Being able to use that overcharge cannon every three seconds is an advantage you sometimes can't afford to be without. As unupgraded commanders become outclassed quickly against T2 units and are all but helpless against T3 units, the overcharge cannon will often be your only chance of survival if your opponent gets the technological edge over you. On the other hand, the overcharge cannon is a deterrent against throwing small numbers of expensive T3 land units against the enemy ACU, especially because of the area of effect.