Understanding the Zone Of Control (vanilla)

Understanding the Zone Of Control
limiting the enemy movements

Introduction

The zone of control (ZOC) is an important aspect of unit movement during combat. The ZOC rule limits the movement of units that are adjacent to enemy units and can be used to protect ranged units, for instance. But misunderstanding this rule may be fatal during a campaign, especially when facing a mobile enemy. This article explains why.

Key Concepts / Abbreviations

Combat Unit - a military unit that can engage in combat against other units or against cities.
Non-Combat Unit (aka Civilian Unit) - a unit that cannot fight, i.e. Settlers, Workers, Work Boats, and Great People (of particular importance, the Great General)
Embarked Unit - a land or civilian unit that is on a water tile.
MP - movement point
LOS - line of sight
ZOC - zone of control

Definition of the Zone Of Control

"Combat units exert a "Zone of Control" (ZOC) over the tiles around them. When a unit moves between two tiles within an enemy's ZOC it expends all of its MPs."
(Civilization V manual, page 53)

Understanding the ZOC rule with some caravels.

This rule must be interpreted as follows:

ZOC: zone of 6 hexes adjacent to a combat unit

ZOC rule: if a unit directly moves one tile within the same enemy's ZOC, it expends all of its MPs.

Let's take the French Caravel as shown on the right. As with every combat unit, it has its own ZOC (delineated in red).
The rule applies to enemies present in the ZOC, like the Roman Caravel, but not necessarily to all enemy movements:

Only direct moves within the (same) ZOC are affected (red arrows)
Other moves are NOT affected. In particular the rule does NOT apply:
- if an enemy enters or exits the ZOC (blue arrow)
- if an enemy exits the ZOC and at the same time enters another ZOC (green arrow)
- if an enemy exits the ZOC and reenters it later (yellow arrow)

Applying the rule

The following examples illustrate typical cases of the ZOC rule.
(Civ V release 1.0.1.383 was used for testing)

Blocking enemy units

Fig. 1: the Longswordsman cannot attack the Crossbowman due to the ZOC of the Pikeman.

Spoiler Fig. 1 :

Fig. 1b: the French Trireme can only move 2 tiles to the east due to the enemy's ZOC

Spoiler Fig. 1b :

Entering and/or Exiting a ZOC does not impede unit's movement

Fig. 2: the French Infantery may enter the enemy ZOC and then exit it and continue its movement, as if there were no ZOC.

Spoiler Fig. 2 :

Walking through the enemies

Fig. 3: the Horseman can withdraw because he first exits the Pikeman's ZOC and enters the Archer's ZOC, and then continues his movement one tile within the Archer's ZOC.

Spoiler Fig. 3 :

Exiting and reentering the ZOC with mobile units (3-4 MPs) to flank the enemy!

Fig. 4: the Horseman exits the enemy ZOC, reenters it and may attack the Archer in the same turn!

Spoiler Fig. 4 :

Fig. 4b: the Trireme can escape because it exits the enemy ZOC, reenters it and may continue its movement.

Spoiler Fig. 4b :

Zigzagging around the ZOC with fast units! (> 4 MPs)

Fig. 5: the Battleship is not really blocked by the enemy, just slowed down.

Spoiler Fig. 5 :

The Trireme can make a sally because embarked units have no ZOC !

Special cases

Cities
- Cities exert a ZOC too, even if there is no garrison. A city ZOC applies to naval and to land units. (see Fig. 6)
- Combat units also exert a ZOC on enemy units stationed in a city. (see Fig. 7)

Embarked Units
- Embarked combat units do NOT exert a ZOC. (see Fig. 8)
- Land and naval units exert a ZOC on embarked units. (see Fig. 11)

Naval Units vs Land Units
- Naval units exert a ZOC on enemy naval units. (see Fig. 1b)
- Naval units also exert a ZOC on enemy land units. (see Fig. 9)
- Land units do NOT exert a ZOC on enemy naval units. (see Fig. 10)

Units able to move after attacking
- A unit that can move after attacking (e.g. a mounted or an armored unit), can kill an enemy within another enemy's ZOC and still continue moving. (see Fig. 11b)

Miscellaneous
- Only combat units exert a ZOC: non-combat units do NOT. But non-combat units must respect the ZOC of enemy units.
- The ZOC rule does not apply at all to air units

Examples and figures

Fig. 6: the Rifleman cannot kill the General due to the city's ZOC.

Spoiler Fig. 6 :

Fig. 7: the Warrior exiting the city is concerned by the Barbarian's ZOC.

Spoiler Fig. 7 :

Fig. 8: the Trireme is not blocked by the embarked enemy.

Spoiler Fig. 8 :

Fig. 9: the Warrior's movement is limited by the Barbarian Galley.

Spoiler Fig. 9 :

Fig. 10: the Trireme is not blocked by the Warrior.

Spoiler Fig. 10 :

Fig. 11: the embarked unit is blocked by the Crossbowman.

Spoiler Fig. 11 :

Fig. 11b: a knight can kill a warrior while passing through another unit's zoc, and still continue moving

Spoiler Fig. 11b :

Dealing with the Zone Of Control

The ZOC rule has an impact when you're moving units (to attack or defend) and when the enemies are doing so.
From a tactical point of view you may take advantage of the ZOC rule in some defensive situations, as explained below.

Tactical overview

the ZOC rule only affects adjacent enemies: thus, an attacking unit entering a ZOC is NOT stopped (unless this move is done within another ZOC). This is a key point to keep in mind when defending.
a unit may always move at least one tile in a turn (unless it is totally surrounded by enemies or obstacles).
the utility of a ZOC decreases with the enemy's mobility:
- slow units (2 MPs) are mostly blocked by the ZOC
- as of 3 MPs, units may flank the enemy, i.e. exit a ZOC, reenter it and still be able to move one more tile within the ZOC to attack on the side! (see Fig. 4)
- fast units (> 4 MPs) may just be slowed down by the ZOC and can reach all tiles within the ZOC in the same turn (e.g. tanks on clear terrain or caravels on water).

remarks:
- roads and railroads increase unit mobility, so a slow unit on a road may also flank adjacent enemies! (like a Horseman on clear terrain)
- conversely, rough terrain generally slows the enemy and may in some situations prevent mobile units from flanking your units.
- poorly spaced units may be fatal in defense because mobile enemies may zigzag between your units, exiting one ZOC and entering the next one several times, avoiding any movement penalty!
- the ZOC rule is more effective at the beginning of the game because early units are generally slow. The rule has less impact in the modern age, when you're dealing with units like Tanks or Destroyers.

Determining the ZOC impact on your units

In some situations the impact of the ZOC rule may not be obvious. Fortunately, the game may help you, as shown in the next figure with a Tank.

First select the unit and then click on the "Move Mode" button: the possible unit movements are displayed in blue and the enemies that can be attacked are circled in red.

Spoiler Fig. 12: Determining the ZOC impact :

Defending with the ZOC rule

The ZOC of your units also has an impact on the enemy and may be used for defensive purposes during the other players' turn. But the computer won't help you here! You'll have to figure out for yourself how your units may block the enemies next turn.

To show the issue, two concrete situations are presented: the protection of ranged units and of embarked units.

Protecting ranged units

As shown in Fig. 14, the ZOC rule may be very effective against a slow unit like a Pikeman (2 MPs) because it adds 4 safe tiles for the defending units (in light blue).

This can be used to defend a city with Archers, or similarly to protect ranged units on clear terrain behind a melee unit.

The following conditions are essential:

your city or melee unit has to be adjacent to the enemy
the enemy should not be able to flank your units.

That's why it does NOT generally work against mobile units like Horsemen, unless you have assistance from rough terrain. A typical pitfall is shown in Fig. 15.

Spoiler Fig. 14: Protecting weak units with the ZOC :

Spoiler Fig. 15: The ranged unit is not protected by the Pikemen because the Knight is too mobile (3 MPs) :

Poor naval defense.

Trying to protect embarked units

If you're playing with the Gods & Kings expansion of Civ V it is not a real issue to protect embarked units because it is possible to stack them with naval military units. It's much more of a challenge to protect embarked units without this expansion, for the following reasons:

with the exception of the Trireme, naval units are very mobile. Ships have 4-8 MPs (without bonuses). And each water tile only costs 1 MP.
most naval units have a very short line of sight (2 tiles) so that they mostly cannot see the threat. Caravels have a line of sight of 4 tiles and may be used as naval scouts.
embarked units have no ZOC and are vulnerable; they cannot engage in combat at sea. An enemy ship only needs to enter an embarked unit's tile to kill it!

The invasion attempt on the right illustrates the issue. The French embarked units are to be protected by some warships and the set up looks at first sight pretty good:

the safe invasion corridor is delineated in green.
the ZOCs of the French ships are delineated in red.
the yellow arrows show potential enemy intrusions blocked by the French ZOCs.
(remember: an enemy may enter a ZOC and then still move one tile within it!)

In fact, the corridor is NOT safe at all, because some important paths were omitted. The red arrows show possible path of attack for enemy Destroyers (8+ MPs), zigzagging through the ZOCs and reaching an embarked unit. Each ship may then continue its movement but, fortunately, can only kill one embarked unit per turn. Otherwise all of the embarked units may have been destroyed!

The reason for this disaster-in-waiting is that the ships are too poorly spaced. In such a situation you'll need one more ship to protect the embarked units. But spacing ships only by one tile is very expensive. That's why it's almost impossible to fully protect embarked units far off shore, and you will have to either deal with some losses, or scout the enemy navy so you know where to concentrate your defenses.

And do not hope the AI will not find the deadly paths, because the computer is much more skilled than humans at path finding!

Known Issues

There is currently a bug for units with movement points beyond their natural limit (Danish units disembarking or Persian units on the turn a golden age ends): when they pass through a ZOC or over a river, they do not expend all remaining MPs. Following spoiler explains the bug in details.

Spoiler ZOC issues :

Conclusion

By limiting the enemy's movements, the ZOC rule is very useful to protect weak units like ranged or embarked ones.
But the rule may have unexpected results: depending on the enemy mobility (and on the terrain), you may protect your rear and side units well, only your rear units, or none of them!

As a rule of thumb: beware of Knights! beware of Caravels!

Patch version of this article: 1.0.1.383

Understanding the Zone Of Control (vanilla)

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