You know, if each individual unit is suppose to represent an army, why not name them as such?
Tank - Armored Battalion
Infantry - actually this ones pretty vague, but to go with the flow could be like Infantry Division?
Marines - I don't know much about the marines, so eh
Bomber - Air Wing
Battleship - Carrier Battlegroup
Submarine - These typically go solo, so maybe just leaving it as is?
Anyways you get the point, since they're not actually individual tanks or infantry, why not have their names represent this fact?