A submachine gun is a firearm that combines the automatic fire of a machine gun with the ammunition of a pistol, and is usually between the two in weight and size. They are the primary weaponry for the Anti-Tank class.
The sub-machinegun (sometimes abbreviated SMG) appeared during the later stages of WWI and was a product of trench warfare. After WW2, the submachine gun's popularity in the military continued but began a slow decline, primarily being replaced by assault rifles.
In BF2, the Anti-Tank sub-machineguns have the lowest overall accuracy and lowest damage per shot of any primary weapon in the game. They do have some utility at point-blank range on full auto, but in most cases an AT player would be better off using their pistol. It takes six hits with an SMG to kill a healthy player. There is no difference in accuracy or damage between the three models, though the full automatic only mode of the Type 85 makes it more difficult to take single shots, and the PP-19 has 15 more rounds per magazine.
Due to the fact that these guns lack power and range, the Anti-Tank unlock, the deadly DAO-12, offers almost unmatched close-quarters firepower.