This is just one of my wished for Civ III: With Civ II (assuming you don't have Leonardo's Workshop) you must manually upgrade your cities defensive units manually. I would like to see an option to have the computer handle this boring task automatically. My suggestion would be, when a better unit comes along, you could shift a percentage of a cities production to upgrading it's defensive units. Note: It wouldn't disband the old unit until the new one was built!