Mass upgrade hotkey is SHIFT-U, not CTRL-U. AI does not mass upgrade, as stated. The gold problem for AI upgrades is significant, humans plan for it, AI doesn't. That may be the fundamental problem here. Even in super defended cities, where you have to bust down tons of Mech Infantry, TOW Infantry, etc. there is always a spearman at the bottom of the pile, that should not be. It should turn into something else, with weak defense/attack, maybe slightly better than its previous stats, to reflect more modern era. Spearman could turn into Militia, with rifles, once AI hits Nationalism and builds its first Rifleman, however, Militia stats would be only 1.3.1, Pikeman could go to 1.4.1, you get the idea. I would have all seriously obsolete attack units, like Medieval Infantry, turn into this kind of DEFENSE unit also - they have no real chance going after the player's cities at that point, better have them defend AI cities. Need new code so the AI can deal with the switched flags for offensive vs defensive unit tactics when this occurs.