Ship

Hearts of Iron IV

Naval warfare

Navy

Ship

Naval missions

Naval battle

Naval technology

Naval doctrine

A ship refers both to a piece of equipment produced by dockyards and, once launched and manned, a member of a task force ready to participate in naval warfare.

Hull types

See also: Naval technology

Hulls are the foundational component of ships, and are unlocked through research. Each hull type contains a number of module slots. These slots can be populated by modules via the Ship Designer in order to form complete ship designs (a.k.a. variants) that can be produced by dockyards.

At the start of the game, each country will have a selection of pre-existing ship variants available for production, based upon hull types which have already been researched.

Some hull types may serve as the foundation for more than one ship type, depending upon the modules that are fitted during the design of a given ship variant. For example, cruiser hulls can serve as the basis for light cruisers or heavy cruisers depending upon the type of guns that are fitted.

Hull types and their corresponding ship type(s) are listed below:

Hull type	Ship type(s)
Destroyer hull	Destroyer
Cruiser hull	Light cruiser Heavy cruiser
Heavy ship hull	Battlecruiser Battleship
Super heavy battleship hull	Super heavy battleship
Carrier hull	Carrier
Submarine hull	Submarine

Ship types

Surface warships are categorised either as capital ships or screen ships, while submarines and convoys have their own unique mechanics.

Capital ships

As the main surface combatants, capital ships are designed to sink enemy ships in surface battles.

• Super heavy battleship (SHBB): SHBBs are particularly powerful and heavily-armored battleships, based upon a dedicated SHBB hull. Unlike other hulls which receive new iterations over the years, there is only one SHBB hull in the tech tree. SHBBs are powerful enough to remain a potent threat throughout the game despite the lack of hull iterations. However, they are also prohibitively expensive and take a very long time to build.
• Battleship (BB): With their heavy armor, battleships are capable of surviving substantial amounts of incoming fire from the enemy battle line. They can also deal considerable damage of their own. Battleships are expensive and take some time to build.
• Battlecruiser (BC): Battlecruisers share the same hull as battleships, but are distinguished by somewhat lighter armor and a lower construction cost. Although they can withstand less damage than a battleship, their lighter weight also makes them faster and harder to hit.
• Heavy cruiser (CA): Heavy cruisers share the same hull as light cruisers, and are distinguished by their heavier guns. With the lightest armor of any capital ship, heavy cruisers have low survivability against battlecruisers and battleships.
• Carrier (CV): Carriers are expensive to build, and are populated by specialised aircraft which must be built separately as well. The combined fuel cost of a carrier and its air wings can be considerable. Once these hurdles have been surmounted, carrier air wings can vie for control of the air and deal bomb damage to enemy ships during naval battle. Outside of naval battle, carriers may also be used as mobile air bases.

Screen ships

Screen ships are named for their ability to protect capital ships and convoys from torpedoes during naval battles.

• Light cruiser (CL): Tougher and more expensive than destroyers, light cruisers are highly versatile and can be outfitted for a range of roles. When equipped with airplane catapults, they can serve as excellent scouts. When dedicated to firepower, they excel at destroying other screens.
• Destroyer (DD): As the lightest screen ships, the strength of destroyers lies in their numbers. During battle, they can form the bulk of a screening line to protect capital ships from torpedoes. Destroyers are also ideally suited to convoy escort missions. Both of these roles call for a sufficient quantity of ships, and destroyers are the most economical vessel to produce in the numbers required. They also boast relatively low fuel requirements. Beyond their basic armament, they can be outfitted with additional guns to increase their effectiveness against other screen ships, or torpedoes to threaten capital ships.

Submarines

• Submarine (SS): Cheap, slow, and stealthy, submarines are frequently used as convoy raiders and minelayers. During naval battle, submarines may be hidden under certain circumstances, which protects them from attack.

Convoys

Convoys are ships which carry land units, resources, reinforcements, and lend-lease equipment across water. They are treated more abstractly than all other ship types, with a variety of unique mechanics.

Convoys are distinguished by the following characteristics:

• Convoys are unarmed.
• The positions of convoys are not shown on the map, regardless of map mode. (Convoy routes can be seen on the strategic navy map mode.) Convoys are only ever directly seen during naval battles, e.g. when a convoy raiding task force automatically interdicts some convoys.
• Damaged convoys do not need to return to dockyards in order to be repaired. Any convoy that is damaged (but not destroyed) during battle will be immediately restored to perfect condition after the battle has ended.
• Convoys that are not currently in use are kept in an abstract reserve, and have no tangible presence in the game world.
• Convoys cannot be directly controlled by the player. However, it is possible to influence convoy routes by setting access levels for specific regions.
• The concepts of hulls and modules do not apply to convoys. Instead, there is only one standard convoy model. There are no technologies available to unlock more advanced convoy models.
• It is not possible to create convoy variants.
• Convoys cannot be named.

Convoys are defenseless against enemy warships, but can be escorted by friendly warships for protection.

Access level

Main article: Strategic region#Naval access level

For any strategic region containing sea provinces, an access level can be set to determine whether ships can enter the region.

Ship details

Left clicking on a ship silhouette in the fleet will bring up its ship details. From here its statistical values are visible, along with any combat history on the second tab. It is possible to rename the ship by pressing its name. Carriers will show the attached air wings. Reorganizing air wings is done through the air wing management system. To scrap/disband a ship press the red trash bin in the upper right corner of the ship detail screen, this will return its manpower to the pool and is an alternative to sending old ships off on suicidal missions.

Carrier air wings

When building a carrier, the player has the option to pre-define how its air wings should be organized. Only carrier (navalized) aircraft may be based on carriers, and must be researched and produced separately from their ground based counterparts. The air wings of existing carriers can be adjusted by selecting the air wing in the air force overview or by selecting an air region in the air map mode, which brings up a list of all bases, and then selecting the fleet the carrier is a part of to bring up the air base windows for all carriers in that fleet. From the (carrier) base window the process is identical to establishing or modifying a wing stationed at an air base.

Viewing combat statistics

Fleet information, history and details

Hearts of Iron IV tracks experience, skill and history for individual ships, and this can be seen in the Fleet View. Select the fleet which the player wants to review. You will notice that each individual ship in your fleet is listed with a green organization and a brown strength bar, a silhouette for the ship class, a rank icon to show the ship's experience level, a vertical progress bar showing how much experience that ship has accumulated towards the next rank and the name of the ship. If the ship has participated in combat and sunk any enemy vessels, an additional icon appears next to the ship name for history. Holding the mouse over this history icon will give you a summary of how many ships the player has sunk with this vessel. Clicking on the history icon will open the ship details pop up displaying the history of ships sunk for that particular vessel.

Statistics

Each class of ship has a number of values referred to as stats. These are described below. Most of these stats can be improved by building a variant. However, be aware that increasing one stat will adversely affect a different stat. Reference Variant and Variant Upgrading and Variant Naval. Researching Naval doctrine can also increase stats.

Base stats

• Maximum speed. Maximum speed represents a value that indicates how quickly a naval vessel can move under optimal conditions. A faster ship has an easier time of disengaging from pursuers, can close to optimal fire range quicker, and can move faster into position when concentrating fleets.
• Maximum range. A ship's range represents its onboard stores of fuel and foodstuffs, which will limit how far it can travel from the nearest friendly Naval Base.
• Evasion. Evasion is the ability of ships to avoid enemy fire through maneuvering. When evaluating chances to avoid being hit, the target's evasion value is compared to the attacker, so that if you have high evasion, then you will also be more capable of hitting evasive targets; evasion is checked against enemy evasion, so high evasion improves hits against high evasion targets. When considering torpedoes, note that they are slow so evasion matters even more. Reference Defines NNavy COMBAT_EVASION_TO_HIT_CHANCE, Defines NNavy COMBAT_EVASION_TO_HIT_CHANCE_TORPEDO_MULT, and Defines NNavy MAX_EVASION_BONUS.
• Organization. Organization is an indicator of a ship's combat readiness. The higher the organization rating of a ship, the longer it can stay in a fight. A ship with low or no organization cannot fight or move effectively. Reference Defines NNavy COMBAT_LOW_ORG_HIT_CHANCE_PENALTY.
• Deck size. Deck size is a measurement of how many planes a carrier can fit on board. The act of exceeding a carrier's deck size (plane limit) is known as carrier overcrowding and it results in a penalty to carrier plane missions. For example, a carrier with a deck size of 45 is limited to a maximum of 45 planes before triggering the overcrowding penalty. Each plane exceeding 45 adds a mission penalty of approximately -4.4% per plane. If the total number of planes on this carrier was 55, then the 10 extra planes would result in a mission penalty of -44%. The Massed Strikes naval doctrine (reference Naval doctrine Massed Strikes) reduces the penalty for crowding too many planes on an aircraft carrier by -30%. In the example above, the Massed Strikes naval doctrine would have reduced the overcrowding mission penalty from approximately -4.4% to -2.2% per plane or from -44% to -22% per 10 planes. The Massed Strikes doctrine's significance is that it allows carriers to get more planes in the air even though over capacity. Bringing more aircraft to a fight is better.
• HP. HP is an abbreviation for "hit points" and is the ability to absorb damage. It represents strength which is how much damage a ship can sustain before being destroyed.
• Reliability. Reliability is the ability of a ship to continue functioning during combat. The lower the value the more likely the ship is of suffering a critical hit. Ships may receive critical hits that are much stronger than usual hits primarily because of exploding ammo or fuel tanks. Increasing a ship's reliability will reduce the chance that a received hit becomes critical. Note that the highest critical chance is done by torpedoes and not by a ship's main guns. Reference attrition and accidents.
• Supply use. How much supply the unit consumes per day. Please read Supply on the significance of this.

Combat stats

• Naval firepower. Naval firepower is a value that represents a ship's capability to damage enemy ships due to gun caliber, quantity of guns, rate of fire, etc. The higher the number, the better. Reference Naval warfare combat details.
• Torpedo attack. Torpedo attack is a value that represents a vessel's capability to damage enemy ships via torpedoes.
• Depth charges. Depth charges are a value that represents a ship's capability to damage enemy submarines via depth charges.
• Armor. Armor is a value that represents a ship's steel decking thickness, belt thickness, bulkheads, etc. The purpose of armor is to help protect a ship from attack. Having armor that is equal to or greater than the opponents piercing value makes you take less damage (-90%); reference Defines NNavy COMBAT_ARMOR_PIERCING_DAMAGE_REDUCTION. Having armor that is equal to or greater than the opponents piercing value also helps prevent an enemy ship from gaining a critical hit bonus; reference Defines NNavy COMBAT_ARMOR_PIERCING_CRITICAL_BONUS = 3.0 and Naval warfare.
• Piercing. Piercing is a value that represents the ability of a ship's guns to penetrate an enemy vessel's armor. Having equal or greater piercing to the target's armor value allows you to do more damage.
• Fire range. Fire range is the maximum effective distance that a ship's main guns can reach.
• Shore bombard. Shore bombard is a capital ship's ability to shell land troops using its main guns.
• Anti-air. Anti-air, also known as Naval AA attack, is a value that represents how much firepower that a ship's anti-air guns can provide in shooting down enemy planes. This value adds a positive modifier to the "to hit" dice of friendly ships' attacks against air units. The higher the number, the better to protect against both land based and carrier based air attacks. The naval AA attack value also protects against port strike attacks. Researching the Grand Battlefleet Naval doctrine increases all of your ships' anti-air values by +10%.

Misc. stats

• Fuel Usage. How much fuel a unit uses while it is operating. Sea units will consume fuel while on active missions or during training.
• Port capacity usage. Port capacity usage is a value that represents the space that a ship requires while in a friendly port.
• Surface visibility. Surface visibility is a value that represents a ship's profile. This value is the "hide in shadows" score. The higher the value, the more visible a surface ship becomes making it more likely to be spotted and attacked. The smaller the value, the less visible the ship becomes making it harder to spot. The enemy can't destroy a fleet it can't see. For example, a Japanese fleet with minimal surface visibility score can sneak its surface fleet past Singapore in the Straits of Malacca. Surface visibility can be reduced (-10%) by hiring a raiding fleet naval design company such as Germany's Blohm & Voss or by researching the proper naval doctrine.
• Surface detection. Surface detection is a ship's ability to detect enemy vessels navigating on top of the sea (not under the sea such as submarines). A fleet can only engage ships if it knows they're there. A ship starts out hidden and has a chance to be spotted if it gets too close to an enemy ship (ships may also be spotted by aircraft). Reference Naval warfare Detection. Surface detection may be increased by the following means:

1. Adding more ships to a fleet or sea region
2. Adding more planes to a sea region (gaining Air Superiority)
3. Increasing radar in a sea region
4. Having better decryption than an enemy vessel's encryption (+20% improved detection for every level that your decryption is better than the enemy's encryption, reference Defines NNavy DECRYPTION_SPOTTING_BONUS = 0.2)
5. Researching higher level ships
6. Researching naval doctrines that include a bonus to surface detection

• Sub visibility. Sub visibility is a value that represents a submarine's outline. This value is the "hide in shadows" score. The higher the value, the more visible a submarine becomes making it more likely to be spotted and attacked. The smaller the value, the less visible the submarine becomes making it harder to spot.
• Sub detection. Sub detection is a ship's ability to detect enemy submarines. A fleet can only engage submarines if it knows they're there. A submarine starts out hidden and has a chance to be spotted if it gets too close to an enemy ship (submarines may also be spotted by aircraft). Destroyers are best at hunting submarines followed by light cruisers due to their high sub detection ability and use of depth charges. Capital ships are poor at sub hunting due to their low sub detection and lack of depth charges. Sub detection may be increased by the following means:

1. Adding more ships, especially destroyers and light cruisers, to a fleet or sea region
2. Adding more planes to a sea region (gaining Air Superiority)
3. Increasing radar in a sea region
4. Having better decryption than an enemy vessel's encryption (+20% improved detection for every level that your decryption is better than the enemy's encryption, reference Defines NNavy DECRYPTION_SPOTTING_BONUS = 0.2)
5. Researching higher level destroyers and light cruisers
6. Creating destroyer and light cruiser variants incorporating higher sub detection
7. Hiring an escort fleet design company such as the United Kingdom's Yarrow Shipbuilders (+10% sub detection for screen ships)
8. Researching naval doctrines that include a bonus to sub detection
9. Adding an anti-submarine specialist (+10%), anti-submarine expert (+15%), or anti-submarine genius (+20%) to the military staff

Unverified stat observations and commentary

• Surface detection and visibility along with sub detection are not precisely accounted for and are simply combined on the fleet level as per value present. A single battleship in a fleet of 100 destroyers will almost nullify any detection and visibility stemming from destroyers.
• Hit points is often a secondary factor to organization, evasion, and armor values since screening ships will often just die or quickly flee from a capital hit, while capital ships will "tank" with armor that reduces damage considerably, particularly if there is a substantial difference between piercing and armor (see explanation here). Aviation damage ignores 2 of these factors more often than not, reducing organization of capital ships that they will target more than anything, most likely not leading to a kill in themselves alone (as in bombers alone).
• Evasion has a hard upper limit on benefits it renders, light cruisers may surpass it.
• Anti-air attack is definitely useless against carrier based air power that will target capital ships (with screening ships' AA doing nothing), flying at least 2 sorties a day, and will always find its target (although capped at a max of 200 total planes per sortie).
• Sub attack is also not much of a factor since investing into airpower+carriers you're more likely to be dependent on carriers to kill revealed submarines rather than expecting destroyers to close in (with researched naval doctrines for escort efficiency), not that subs have much health for it to be a truly competitive matter to begin with.
• Shore bombardment has an upper limit on benefits it may render which requires only a few battleships.
• Torpedo attack fires every 4th time, has a 20% chance of being critical and doing decent damage, and may miss altogether (ignores armor, so a bunch of destroyers could kill a lone heavy ship).
• Operational range The operational range of a unit indicates the radius of operation for that particular type of ship on the map, from the closest friendly port (regardless of where the home port for the fleet containing that ship is based). A fleet that combines ships with different operational ranges will have a range that is the average of the individual ships.

Warfare