Upgrade (Civ4)

Older military units in Civilization IV may upgrade to newer unit types, gaining increased combat strength and possibly other abilities.

Conditions for Upgrading

A unit can upgrade to a new unit type when the following conditions hold:

• the new unit type is an allowed upgrade for the unit
• the civilization has the technology allowing the new unit type
• the civilization has enough money in its treasury to afford the upgrade cost (see below)
• the unit has not expended all of its movement points that turn
• the unit is within its own cultural boundaries, or those of an ally
• the city (of its civ) that the unit is nearest to has access to any strategic resources necessary to build the new unit type

When all of the conditions above hold, you will see an "Upgrade to X" button lit up (active) when you select a unit that can do that upgrade. When you have the technology that allows an upgrade, but one or more of the other preconditions do not hold, then you will see an "Upgrade to X" button but it will be darkened (inactive).

Upgrade Cost

Upgrading a unit with a merged Great General is always free. Otherwise, there is a cost called the upgrade cost. The cost for a human player to upgrade a unit is computed based on its hammer cost compared to the hammer cost of the new unit type, as follows:

cost = 20 + 3*(hammercost(new) - hammercost(old))

For example, upgrading a musketman (cost 80 hammers) to a rifleman (cost 110 hammers), costs 110 gold.

The upgrade cost for AIs is dramatically reduced from what human players have. If you know the details, please add them here.

Effect of Upgrading

When a unit is upgraded, the following effects happen:

• it is replaced by unit of the newer type. Its hitpoints and promotions are not changed.
• it loses any inherent abilities of the old type, while gaining any inherent abilities of the new type
• it loses all remaining movement that turn
• it is unfortified
• it gains any promotion that is inherent for the new unit type
• it has its current experience decreased to 10, if it has more than that (exception: not if it has a merged Great General)
• the upgrade cost is subtracted from the treasury of its owning civ