Unlike the real world, the Submarine in Civilization VI has a rather limited scope of use, and will often be ignored throughout the game for the following reasons:
- Overall, naval warfare does not carry such importance as it did in Civilization V. The fact that cities now can be settled inland and still reap the benefits of being coastal cities, together with the value of water tiles compared to land tiles, makes wresting control of the sea low on the priority list. Unless the map is heavily dominated by water, most of the time you can get by without owning a single ship.
- Submarines are unlocked at the same time as Battleships, yet pale in comparison to them in most regards.
- The best selling point of Battleships is that they have a Range of 3, meaning they can hit targets farther inland. In game, 3 tiles is the maximum distance that you can settle from the Coast while still being able to build a Harbor. Meanwhile, Submarines only have a Range of 2, meaning tactical settling can render this unit useless.
- Submarines have 2 less Movement than Battleships (i.e. are 40% slower). When thinking of naval warfare as land warfare waged solely on flat land, there is a great emphasis on maneuverability and reach, in both of which the Submarines are outclassed by the Battleships.
- Coastal raiding is no longer important when Submarines are unlocked. Wars in the late game can be damaging towards both the attacker and the defender; if you're planning to wage a war, you'd better make sure it's worth your while. Capturing opponents' cities and weakening their infrastructure is more important than harassing them and disrupting their economy at this point, and Battleships are better at attacking cities than Submarines.
- In Gathering Storm, Submarines use Oil Oil and Battleships use Coal Coal. Overall, Coal Coal is less valuable than Oil Oil in terms of availability and the number of applications for each resource. In vanilla Civilization VI and Rise and Fall, however, Submarines can be built without resources, giving them at least one advantage over Battleships.
- Invisibility as an ability is nice early in the game on units with invisibility promotions like Scouts or Warrior Monks, since the enemy does not have a lot of counterplay. However, considering the archenemy of Submarines, the Destroyers, are unlocked right afterwards at Combined Arms, this aspect does not feel too strong anymore. For civs that are far from unlocking Destroyers, they are probably too weak to pose any threat; for civs that are close to unlocking or have unlocked Destroyers, you cannot do anything about them.
In the expansions, there is one situation in which you may want to put a higher priority on building Submarines. If you're in a Dark Age and have slotted Letters of Marque, all your naval raider units will have +2 Movement and you'll receive a 100% Production bonus toward training them. This will make your Submarines faster than Destroyers and just as fast as Battleships, and possibly allow you to train enough of them to achieve naval dominance (especially if they earn the Homing Torpedoes, Silent Running, and Wolfpack promotions, which will allow them to severely damage or destroy opponents' ships and retreat before they can react). Once you unlock Telecommunications and upgrade your Submarines to Nuclear Submarines, you'll have an even more pronounced advantage.
Note that, unlike in Civilization V, Submarines cannot enter Ice tiles.
Civilopedia entry Edit
When those madcap Confederates in the Hunley sank the USS Housatonic in 1864 AD, it launched a new age of naval warfare; unfortunately, the Hunley also sank itself, taking its crew to the bottom as well. Nevertheless, the submarine had made its stealthy appearance. The submarine, submersible, U-boat is a craft made for sneaking up on a target while underwater and then sinking it with torpedoes … or if possible surfacing and using its pathetic deck-guns. Germany pioneered their use as merchant raiders – really effective ones – during WW1, and expanded upon it during WW2, eventually sinking some 14.5 million tons of enemy shipping (including the odd warship) from 1939 through 1945. Advances in ballast tanks, power plants, control planes, hull plating and such sparked a “submarine-race” between the post-war superpowers culminating in nuclear-powered, deep-diving boats … armed with nuclear missiles that could be launched at population centers. What has the Hunley wrought?
- The Submarine's model is based on the American Gato-class submarine.