Civilization 6 - Nuke Defence

Introduction #

Over the last weeks my friends and me started playing Civilization 6. While it has been a ton of fun so far we always seem to run into a similar problem every game. Once the first of us researches the Nuclear Fission technology and completes the Manhattan project he gets rather trigger happy and proceeds to obliterate another player by nuking all of his towns.

This typically leads to various savage insults and more often than not a rage quit of the affected player. To avoid such circumstances I’ve been trying to figure out how one can defend against the threat of nuclear devices. There are some great sites on the internet which provide basic information about this topic such as the Civ6 wiki. However none of the sources that I consulted felt like a real guide. Instead I always had to collect relevant facts from multiple web pages which was rather cumbersome.

To help other players out there I try to provide a comprehensive guide about the defence against nukes in Civilization 6 with this blog entry.

Nuke related technologies #

Let’s start with the technologies that are relevant for nuclear bombs and appropriate counter measures. The following picture shows an excerpt from the Modern, Atomic and Information Era of the technology tree, which highlights important techs. To enlarge the image just click on it.

• Technologies marked in yellow are required for the production of nukes and their different deployment methods
• Technologies marked in red grant access to defensive units that are important in regards to nukes
• Advanced Flight is a special case as it provides both offensive and defensive units in regards to nukes. It is therefore marked in orange.

I will reference the different technologies during the next chapters so keep them in mind. To get a nuke a player first needs to research the Nuclear Fission technology from the Atomic Era. Once this is done he can start the Manhattan Project. Upon its completion nuclear devices can be produced in all of the players cities given that he has enough uranium. Once a nuke has been built it will be added to the players inventory and can be deployed. Which leads us to our next topic.

Nuke deployment methods #

There are four ways to deploy a nuclear device:

• Missile Silo - tile improvement unlocked by Rocketry
• Nuclear Submarines - Information Era naval unit unlocked by Telecommunication
• Bomber - Atomic Era air unit unlocked by Advanced Flight
• Jet Bomber - Information Era air unit unlocked by Stealth

The firing range of a nuke is independent of the chosen method and always the same (12 tiles for a normal nuclear device and 15 tiles for a thermonuclear bomb). Even though these approaches all seem very similar it’s important to keep them in mind as the defensive strategies differ for each method.

Defensive units with Anti-Air capability #

To intercept incoming nuclear attacks we need units that have Anti-Air (or short AA) capabilities. While progressing through the technology tree the following units are unlocked:

• Battleship - Modern Era naval unit unlocked by Refinery
• Missile Cruiser - Information Era naval unit unlocked by Lasers
• Anti-Air Gun - Atomic Era ground unit unlocked by Advanced Ballistics
• Mobile SAM - Information Era ground unit unlocked by Guidance Systems
• Fighter - Atomic Era air unit unlocked by Advanced Flight
• Jet Fighter - Information Era air unit unlocked by Lasers

The Fighter and Jet Fighter are somewhat special as they don’t possess Anti-Air Strength like the other mentioned units. However they can attack incoming enemy aircraft and are therefore still important for this topic.

Basic Interception Mechanisms #

All units mentioned in the previous section can defend against incoming nuclear strikes (at least to some degree which we will see later on). Before going into more detail I want to cover the basic interception mechanics as they are more or less the same for all of them.

A defensive unit tries to intercept attacks that are either targeted at the tile where it is located or at directly adjacent tiles. The following picture shows a visual representation:

All fields highlighted in yellow are within interception range of the Anti-Air Gun. All other tiles are not protected.

It’s important to keep in mind that a unit will only perform an interception if the attack target is one of the protected fields. Interception won’t happen if the nuke is just flying over the protected tiles to reach its destination.

The same rules apply to Fighters and Jet Fighters. However there is an additional fact that you have to keep in mind about these air units. They can only intercept enemy aircraft while they are on patrol. Fighters that are just idling inside an Aerodome won’t provide you support.

Nuke interception #

Now that all of the prerequisite basics have been covered we can talk about the actual interception possibilities. The following table shows the possible combinations between delivery methods and defensive units as well as whether an interception will be successful in this case or not.

Delivery Method	Interception Method	Intercepted?
Missile Silo	Anti-Air Gun	Yes
Missile Silo	Mobile SAM	Yes
Missile Silo	Battleship	Yes
Missile Silo	Missile Cruiser	Yes
Missile Silo	Fighter	No
Missile Silo	Jet Fighter	No
Nuclear Submarine	Anti-Air Gun	No
Nuclear Submarine	Mobile SAM	Yes
Nuclear Submarine	Battleship	No
Nuclear Submarine	Missile Cruiser	Yes
Nuclear Submarine	Fighter	No
Nuclear Submarine	Jet Fighter	No
Bomber	Anti-Air Gun	Yes*
Bomber	Mobile SAM	Yes*
Bomber	Battleship	Yes*
Bomber	Missile Cruiser	Yes*
Bomber	Fighter	Yes*
Bomber	Jet Fighter	Yes*
Jet Bomber	Anti-Air Gun	Yes*
Jet Bomber	Mobile SAM	Yes*
Jet Bomber	Battleship	Yes*
Jet Bomber	Missile Cruiser	Yes*
Jet Bomber	Fighter	Yes*
Jet Bomber	Jet Fighter	Yes*

The delivery method that is the easiest to defend against is the Missile Silo. All ground and naval units with Anti-Air capabilities will destroy incoming nukes fired from this tile improvement assuming that the target is within interception range as described in the previous chapter. The Fighter as well as the Jet Fighter are unable to defend against this type of attack.

Nukes fired from a Nuclear Submarine are a little more complicated. They can only be intercepted by ground and naval units from the Information Era that have Anti-Air capabilities (Mobile SAM and Missile Cruiser). Just like with the Missile Silo nukes fired from a submarine can’t be destroyed by air units.

Attacks from Bombers and Jet Bombers are a special case. In theory they can be destroyed by all defensive units that were introduced earlier in this blog post. However in contrast to the Missile Silo and the Nuclear Submarine there is an additional requirement for the interception to be successful. When a nuke is delivered by a bomber the unit can get attacked by both ground/naval units with anti-air capabilities and patrolling air units. This interception follows the basic air combat rules and the nuclear strike is only averted if the deliverers HP are reduced to 50 HP or less. While this may seem pretty straight forward at first glance it can be quite difficult to apply in practice and be aware of the consequences. Because of this I want to dive a little bit deeper into the topic of defending against attack carried out by bombers.

Damage calculation #

Since we need to reduce the deliverers HP to 50 or less to fend off a nuclear bombing strike it’s important to know how damage is calculated in the game. According to the Civ 6 Wiki article about Combat the following formula is used to calculate the damage that the defender receives:

\(DMG = RAND(0.8-1.2) * 30 * e^{Strength\text{\textunderscore}Difference \over 25}\)

Where:

• RAND(0.8-1.2): A random number between 0.8 and 1.2
• e: Euler’s number
• Strength_Difference: result of the attacking unit’s strength subtracted by the defending unit’s strength

In the case of nuclear attacks there are two important things to keep in mind:

1. Air Units have different types of strengths. For example a Fighter has both a Combat and a Ranged Strength value, while a Bomber possesses Combat as well as Bombard Strength. During damage calculation only the Combat Strength is taken into account. Units that have an Anti-Air Strength such as the Battleship or the Mobile SAM use this value during interception.
2. Even though the bomber delivering a nuke can be considered the aggressor, during interception it is treated as the defender while the intercepting unit is regarded as the attacker.

Let’s have a look at a basic example to get a better understanding. Assume that a full life Bomber (100 HP) attacks a tile that is within interception range of a single Anti-Air Gun. The Bomber has a Combat Strength of 85 while the AA-Gun possesses an Anti-Air Strength of 90. Since the AA-Gun is considered the attacker during interception the Combat Strength of the Bomber is subtracted from the Anti-Air Strength of the AA-Gun to calculate the Strength Difference of the two units.

If we plug in these numbers into the formula from above we get the following result in the worst case

\(DMG = 0.8 * 30 * e^{90-85\over 25} \approx 29\)

and the following result in the best case

\(DMG = 1.2 * 30 * e^{90-85\over 25} \approx 43\)

This means that the Anti-Air Gun will deal between 29 and 43 damage to the Bomber. Nuke interception won’t be successful in this case as we need to do at least 50 damage to a full life Bomber. However if the Bomber is already damaged from previous battles then the interception can be powerful enough to bring the HP down to 50 or less and destroy the nuke.

Support Bonus #

As seen in the previous example a single Anti-Air Gun is typically not able to intercept a nuclear bombing run. However it’s possible to enhance its strength through a so called Support Bonus: An intercepting unit receives +5 Anti-Air Strength for every other anti-air unit to which it is adjacent. Have a look at the following image:

Anti-Air Guns are stationed on the fields marked 1, 2 and 3. Assume that a Bomber is attacking the tile marked with an exclamation mark. At first glance one may think that both Anti-Air Guns on tile 1 and 3 will try to intercept the attacker. However that is not the case. As all three units belong to the same unit type (support) only one of them will attack the bomber. This interception is always performed by the unit with the highest Anti-Air or Combat Strength. In our example both Anti-Air Guns have the same AA value hence one of them is selected randomly. Let’s assume the unit on tile 1 is chosen.

The Anti-Air Gun now receives +5 Anti-Air strength for every other anti air unit that is adjacent. Both the Anti-Air Guns on tile 2 and 3 are neighbouring tile 1 hence the intercepting unit will receive an additional 10 Anti-Air strength. It’s important to keep in mind that even though the attacking bomber is outside of the interception range of the Anti-Air Gun on tile 2 the support bonus is still granted to the unit on tile 1.

Since the Anti-Air Gun that performs the interception now has an Anti-Air Strength of 100 let’s have another look at the damage calculation. If we put the numbers in the formula we get the following result in the worst case

\(DMG = 0.8 * 30 * e^{100-85\over 25} \approx 43\)

and the following result in the best case

\(DMG = 1.2 * 30 * e^{100-85\over 25} \approx 65\)

While interception is not guaranteed under these circumstances it is definitely possible. The Support Bonuses are even granted for units of different eras. So an Anti-Air Gun will provide a +5 bonus to a Mobile SAM assuming both units are adjacent to each other. Of course the same bonuses also apply to air units so a Fighter can provide +5 Combat Strength to another Fighter. However please be aware that this type of Support Bonus is not granted between different unit types. Hence a Mobile SAM won’t provide a bonus to a Jet Fighter.

As you can see Support Bonuses are a helpful way to boost your chances for a successful interception.

Combining Ground and Air units #

Another way to boost your defensive capabilities against nuclear bombings is to combine Anti-Air and Air units. If an attacked tile is within interception range of both entity types then two separate interceptions will take place. One from the ground based Anti-Air and another one from the Air unit. This is the case because the units are of different types. While the Anti-Air Gun is considered a support unit the Fighter is an Air Fighter unit. Have a look at the following picture

Here an Anti-Air Gun (90 Anti-Air Strength) is stationed on the tile while at the same time a Fighter (100 Combat Strength) is patrolling it. If a Bomber were to attack the city or a tile beneath it then two separate damage calculations will take place. During the interception with the Fighter the Bomber will take between 43 and 65 damage while during the battle with the Anti-Air Gun it will receive another 29 to 43 damage. This leads to a combined amount of damage of 72 to 108.

Interception is always successful in this case and if the random value is high enough then the bomber will be completely destroyed!

This combination is a very effective way to guard your cities against nuclear strikes assuming you have enough Aluminium to afford the maintenance costs of the Fighters. The Anti-Air Gun will protect you against launches from missile silos while both units together defend against Bombers. Keep in mind that you should upgrade the units once you reach the Information Era to protect yourself against strikes from Nuclear Submarines and Jet Bombers.

Giant Death Robot #

There is an additional unit with Anti-Air Strength that I haven’t mentioned thus far: the Giant Death Robot (GDR) which is unlocked by the Robotics technology at the end of the Information Era. However it initially only has 90 AA Strength, which is just the same as an Anti-Air Gun from the Atomic Era.

To make the GDR actually useful for interception purposes you additionally need the Advanced AI technology from the Future Era. It grants all robots the Drone Air Defence upgrade, which increases their Anti-Air Strength to 130. With this a single GDR will always intercept incoming Bombers and even Jet Bombers (which have 90 Combat Strength) successfully.

Nevertheless the main problem of this unit is that the required upgrade is only unlocked in the Future Era where it may already be too late. And without the upgrade a Mobile SAM will outperform the robot. However GDRs can be a situational solution during the very late stages of the game as they require Uranium instead of Aluminium for maintenance.

The problem with Thermonuclear Devices #

Once players reach the Information Era they can research Nuclear Fusion and after completing Project Ivy they are able to build Thermonuclear Devices. These upgraded nukes can be deployed via the same means as their predecessor, but they now have a range of 15 tiles instead of 12. The basic defence principles that were explained in the previous sections also remain valid.

However hydrogen bombs have a blast radius of 2 tiles instead of 1 like the normal nukes. This means that they can be deployed outside of the defensive units interception range and still damage the protected tile. Have a look at the following image for a visual representation:

The city Eridu is protected by two defensive units. If an enemy deploys a Thermonuclear Bomb on the field marked with an exclamation mark then it can’t be destroyed as the tile is not within interception range of the Fighter or the Anti-Air Gun. At the same time Eridu will be crushed as it is within the blast radius of the bomb.

To safeguard a city against thermonuclear bombings the defender needs to place units on the city itself as well as four additional spots. The following picture shows one example for such four tiles:

Once defensive units are stationed on all mentioned spots then every tile, where the deployment of a Thermonuclear Bomb would lead to the destruction of the city, is within interception range of at least one guardian.

However this type of defence is rather expensive especially if you use Air units which require Aluminium per turn to maintain. Hence it may not be feasible to protect all of your cities this way.

Summary #

This concludes my guide about defence against nuclear attacks in Civilization 6. As a kind of TL;DR the following bullet point list highlights the key aspects of all the information that was discussed in the chapters.

• Nukes can be delivered via Missile Silos, Bombers and Nuclear Submarines
• Defensive units include the Anti-Air Gun, Mobile SAM, Fighter, Jet Fighter, Battleship and Missile Cruiser
• Launches from Missile Silos can be intercepted with Anti-Air Guns, Mobile SAMs, Battleships and Missile Cruisers
• Launches from a Nuclear Submarine can be intercepted by Mobile SAMs and Missile Cruisers
• Nuclear bombing runs can be intercepted by all units however the HP of the Bomber has to be reduced to 50 HP or less
• Interception Range of defending units is 1 tile
• Thermonuclear bombs are a pain to defend against because of their increased blast radius

Closing Words #

We have reached the end of this post about defence against nuclear devices in Civilization 6. Thanks for reading and I hope that the information provided is helpful to you. Until the next blog post!