Machine Gun - This class has over twice the reload speed of the basic Tank. Its bullets also spread a lot more than the bullets of the basic Tank, making these more difficult to avoid but also less accurate. Its turret is shaped like a trapezium instead of a rectangle.
Face lower tier Tanks first: until you become strong enough, it is recommended not to take on tier 4 tanks.
Fire at the enemy: always try to fire into the enemy's bullets in order to dissipate them. Also use the wider spread to your advantage and cover them from both sides while avoiding their bullets.
Attack snipers: These have better penetration and thus might reach your hull despite your cloud of bullets.
Get into group fights: Avoid being surrounded by multiple enemies, which will cause your inevitable death, since you can only shoot in one direction.
Against Machine Gun:
High penetration: Use tanks with high penetration like the Destroyer, Assassin, Ranger and Overseer branches. These can penetrate the cloud of bullets the Machine Gun creates.
Necromancer: Don't use the Necromancer to attack a Machine Gun. Your squares will absorb the bullet's damage completely to later disappear, resulting in an inevitable death, unless your drones are very fast.
The Machine Gun is the class with the fewest upgrades on it's branch (6 upgrades in total).
Before the Gunner was added to the game, Machine Gun had the option to be a Tier 3 class as well.