Games Like Fire for Effect

The city is under bombardment. You cannot stop their siege. But with your gun and the few defenses remaining you can delay the inevitable for a few more hours, and give the last few remaining survivors a chance to escape.
You play as a survivor wielding a detached heavy artillery piece. This is your only weapon, but its shells can knock the enemy's shells into each other, potentially causing a chain reaction that can wipe the screen of enemies.