The list of units
Tanks are fast-moving offensive units that can attack multiple times in a single turn and withdraw from combat if they are losing (unless fighting another fast unit, of course).
A city must have both oil and rubber in its Strategic Resource box to build tanks.
The rise in the use of semi-automatic and automatic firearms in the late 19th and early 20th century led to the demise of horse-mounted cavalry. As a result, attackers lost a significant advantage in both scouting and deployment. It was only with the development of tanks, armored mobile attack vehicles equipped with high caliber-guns, that a weapon was found which could once more punch a hole through enemy field forces. First appearing in World War I, armored attack vehicles move quickly and strike with power, while still possessing an effective defensive strength. Tanks are powerful weapon against any ground unit.