Due to the dreadnought's large size and heavy armor, the dreadnought gains proficiency with heavy armor , and a +2 bonus to AC

Due to the mechanical nature and size of the dreadnought it is non-dexterous giving a -2 to DEX and reducing it's movement speed to only 15 ft. per round

The dreadnought is immensely tough giving it a +2 to CON and a +2 to STR as well as a +1 to a score of choice

The dreadnought was made to see all targets, including those in the darkness. The dreadnought gains 120 ft. of darkvision

The dreadnought has resistance to non-magical slashing, bludgeoning, and piercing damage types due to it's hard armor

The dreadnoughts large size and strength allows it to wield large battleaxes, Warhammers, and shields

The dreadnought has weapons build into their body:

Heavy Flamer: Cone of 15 ft. 3d6 fire damage, DEX save (8+CON+Proficiency Bonus) for half damage. the damage for this trait increases at 5th Level (5d6) 11th Level (7d6) and 17th Level (9d6)

Assault Cannon: 120 ft. ranged attack. 2d8 lightning damage. the damage for this trait increases at 5th Level (4d8) 11th Level (6d8) and 17th Level (8d8). 

Saw blade: 5 ft. melee range. 4d6 slashing damage. the damage for this trait increases at 5th Level (6d6) 11th Level (8d6) and 17th Level (10d6).