Cannon

The Cannon is a T3 heavy weapon great for taking on armored bases. It pierces through structures and has an area of effect detonation upon impact. It requires a Munitions Plant, or just the Factory in the campaign. Cannons pierce through one layer of armor and a few pieces of bracing.

Advantages

 * Explosive damage with area of effect
 * Pierces through armor
 * Can't be reflected
 * Cheaper than Laser
 * Pierces through shields
 * Great at sieging bases and destroying Reactors from a radius.
 * it can pierces through energy shields unlike the 20mm.

Disadvantages

 * Costly, but more cost-effective than the Laser
 * Requires technology devices
 * Shells have bullet drop
 * Extremely explosive upon destruction

As the Cannon
This weapon is a strong option for the late game. It deals a lot of damage and works well even against strong defenses. It has a height of about 2.5 units, so turn off the grid and build taller boxes to place it in. It's a good idea to build a few of these together to maximize impact.

It costs just enough to be built on a single metal storage, unlike the laser. It costs quite a bit of energy per shot, so energy generation is important. Be sure to protect it while it's building with solid foreground bracing, and once construction has started try to upgrade to at least one metal door to stop pesky explosions (if there are a lot of them coming in, as many as three doors might come in handy!).

Against the Cannon
Firebeams can destroy Cannon projectiles with ease, Cannon projectiles are also weakened by Sandbags and Armor. Although with enough cannon.

Since Cannons are extremely explosive when destroyed, you should always try to aim for a Cannon near the enemy's Reactor because of this weakness. If a Cannon isn't near their reactor then you could always try to doorsnipe a Cannon below another Cannon because usually the Cannon above drops and collapses the entire base.