Naval doctrine

Hearts of Iron IV

Naval warfare

Navy

Ship

Naval doctrine is a technology group that allows a nation to specialize the way its navy conducts naval warfare. The doctrine tree consists of three exclusive branches that provide different bonuses.

Base time to research[edit]

Each individual doctrine research has a base time to research of 255 days. By spending 100 Navy experience the research speed can be increased by 100%. All other research speed modifiers are added to this.
Research time example:
With the 100% research speed bonus from 100 Navy experience spent,
and the 10% research speed bonus from Free Trade,
the resulting research time is:
${\text{Research Time}}=255/(1+100\%+10\%)=255/2.1\approx 121{\text{ days}}$

Doctrine branches[edit]

Fleet in Being: "A strong fleet focused around battleships means that we are a force to be reckoned with when deployed at sea."

This is the well-rounded general purpose set of naval doctrines that most substantial navies used. It enhances Search & Destroy for capital ships, submarine detection for screening ships, and bonuses for all classes, although subs seem least favored. This is the most powerful doctrine for surface action. It is the most efficient in responding to the escort needs of convoys and in anti-submarine warfare.

Trade Interdiction: "Against a stronger naval opponent we can focus on tying up their fleet and destroying supply lines to starve their war machine."

This is an offensive doctrine focusing on attacking enemy convoys with coordinated stealthy surface and submarine raiders that have superior abilities to find and destroy enemy shipping while evading enemy detection. Such stealthiness can also be valuable in normal combat or escaping from it, which is usually the best course. Submarines are made very dangerous to the enemy. The trade-off under this doctrine is that light cruisers and destroyers have mediocre anti-submarine warfare capabilities and weak escort efficiency bonuses, so vulnerable friendly shipping may require more effort to defend. Germany adopted the raiding strategy in its efforts in both world wars to strangle Great Britain by cutting off its shipping, but this can also be suitable for minors seeking a naval presence to strike enemy trade with moderate risk and expense.

Base Strike: "With a strong focus on carriers and their support, no enemy will be outside our reach, whether on land or at sea."

This is similar to the approach of Japan and the United States. It focuses on blue water navy carriers and their light cruiser and destroyer screens, with submarines also receiving decent bonuses for supporting carrier operations. There are no class-specific bonuses at all for battleships, battlecruisers or heavy cruisers, but if built they share the array of global bonuses under this doctrine. Having at least a few fast heavy cruisers that can keep pace with the carriers for bombardment and surface action is advisable, but it is possible to focus just on research and production of carriers, screens and carrier aircraft to make the best use of limited resources.

Some nations start the game with a pre-enabled naval doctrine:

Doctrine	Countries
Base Strike	Japan United States
Fleet in Being	Australia British Malaya British Raj Canada China France Italy New Zealand South Africa Soviet Union United Kingdom
Trade Interdiction	Germany

Note: It's possible to change doctrine throughout the game, but all bonuses from the old doctrine are lost, as if completely abandoned, when starting research of a different doctrine tree.

Definitions and terminology[edit]

Ship modifiers[edit]

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.
Attack Attack is a value that represents a capital ship's firepower or damage capability due to it's gun size, quantity, rate of fire, etc. This value adds a positive modifier to the "to hit" dice of a large friendly ship. The higher the number, the better. Reference naval combat details.
Carrier overcrowding Reduces the penalty for having too many planes based in a carrier.
Enemy fleet size penalty Increases the penalty the enemy gets when they have many more ships in combat.
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.
Naval AA attack Increases the likelihood of landing hits on enemy aircraft, and reduces the effects of Port Strikes.
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.
Surface detection How well ships can detect enemy vessels on the surface.
Sub detection How well ships can detect enemy submarines.
Surface visibility How well a ship is hidden from detection.
Torpedo reveal chance How likely submarines are to reveal themselves when they fire at an enemy equipped with sub detection. Submarines have a base score of 3.5%, modified by visibility and positioning. While destroyers and light cruisers can also be equipped with torpedoes, as surface ships they use different concealment mechanics.

Mission modifiers[edit]

Escort efficiency How quickly ships assigned to Convoy Escort missions can come to the defense of convoys. At 100%, escorts will immediately enter combat upon a convoy coming under attack.
Minelaying efficiency Affects overall efficiency of naval minelaying performed by fleets.
Naval air agility from carriers Modifies the agility of planes executing naval strike missions from carriers.
Naval targeting How likely planes assigned to Naval Strike and Port Strike missions can hit enemy ships.
Port strikes Increases the number of planes assigned to Port Strike missions that can actually participate in combat.
Raiding efficiency How quickly ships assigned to Convoy Raiding missions can gather upon spotting a target.
Sortie efficiency: Sortie (sorties are air missions launched from an aircraft carrier) efficiency represents the speed of refueling and rearming planes on a carrier during battle. A higher sortie efficiency rating results in greater numbers of carrier based planes (not land based) joining in a fight. Sortie efficiency typically starts at 50% (reference Defines NNavy BASE_CARRIER_SORTIE_EFFICIENCY = 0.5) meaning that only half of your carrier planes may fly at the same time. Sortie efficiency can be increased via Naval doctrines and by adding a Navy Carrier specialist (+10%), Navy Carrier expert (+15%), or Navy Carrier genius (+20%) to your military staff.
Strike force org loss How much organization is lost by ships moving while assigned to Strike Force missions.

List of all doctrines[edit]

Fleet in Being[edit]

Fleet In Being

Battleship, Battlecruiser, Heavy Cruiser:

Organization +10

Light Cruiser, Destroyer:

Surface detection +10%

Naval minelaying efficiency +10%

Ships stay in port where they are safer and only engage enemies at opportune moments. The presence of our ships will make enemies more reluctant to take our ports.

Battlefleet Concentration

Battleship, Battlecruiser, Heavy Cruiser:

Organization +10

Strike Force Org loss −20%

Call in nearby ships as soon as an enemy vessel is spotted. Coordinated focused fire quickly render enemy ships useless. Hunt them down one by one.

Convoy Sailing

Destroyer:

Sub detection +5%

Organization +10

Escort efficiency +5%

Introducing compulsory convoy sailing will make it easier to spot enemy raids and respond in time. Safety in numbers is the way to go.

Submarine Operations

Submarine:

Surface detection +5%

Organization +10

Torpedo reveal chance −5%

We do not need to engage the enemy fleet head on to win the war. Strike at their trade convoys before they can react and disappear below the surface again. You cannot fight what you cannot see.

Subsidiary Carrier Role

Carrier: Organization +10
Sortie efficiency +10%

Carriers support Battleships, improving their readiness in switching from defense to offense. The utility of the Carrier as both an eye in the sky and powerful quick strikeforce complement the slower Battleships well.

Convoy Escorts

Destroyer:

Sub detection +5%

Organization +10

Escort efficiency +10%

Fast surface ships as part of our convoys will allow us to spot enemy submarines and respond in time. Detection is they key to eliminating the submarine nuisance.

Undersea Blockade

Submarine:

Surface detection +10%

Organization +10

Submarines are the perfect tool for cutting of the enemy's inflow of important raw materials. We will cripple the enemy's production and win by starving them out.

Hunter Killer Groups

Destroyer:

Sub detection +10%

Organization +20

Light Cruiser:

Sub detection +20%

Organization +10

Escort efficiency +5%

Destroyers form groups to hunt down enemy submarines. The combined efforts of scouting and hunting specialists make a fantastic killing team.

Escort Carriers

Carrier: Sub detection +25%
Escort efficiency +15%

The area covered by a Carrier's aircraft makes escorting trade convoys a much easier task. Securing the flow of resources is essential.

Convoy Interdiction

Submarine:

Torpedo reveal chance −10%

Improved coordination of our submarines will let them strike at trade convoys en route. Disrupting the enemy's supply lines will give us the strategic advantage.

Floating Fortress

Battleship: Organization +20
Capital ship armor +10%

With battleships on highest alert we will always be prepared to respond if the enemy dares threaten our waters. Any fleet needs a solid foundation and the power of the battleship is unparallelled.

Integrated Convoy Defense

Destroyer:

Sub detection +10%

Organization +20

Light Cruiser:

Sub detection +15%

Organization +10

Carrier: Sub detection +25%
Escort efficiency +10%

Better navy and air coordination allow us to strike at enemies from miles away before they are near our trade convoys. This will drastically increase the effectiveness of convoy sailing.

Submarine Offensive

Submarine:

Reaching the pinnacle of communication between our submarines allows them to go on the offensive. Let us destroy the enemy trade convoys faster than they can replace them.

Floating Airfield

Carrier: Organization +20
Sortie efficiency +20%

Improved integration of Carriers into our fleet keeps us prepared to strike from both sea and air. It is key that we dominate the air wherever we go.

Grand Battlefleet

Battleship, Battlecruiser, Heavy Cruiser:

Organization +20

Naval AA attack +10%
Capital ship attack +10%
Naval minelaying efficiency +10%

Leadership training allow our commanders to keep calm in the heat of battle even when commanding immense fleets. Our fleet will crush any opposition head on.

Trade Interdiction[edit]

Trade Interdiction

Submarine, Light Cruiser, Heavy Cruiser:

Surface detection +5%
Organization +10

The sooner we spot the enemy ships, the sooner we can destroy them. Hit their trade convoys and escape before they have time to react.

Raider Patrols

Light Cruiser, Heavy Cruiser:

Patrols of both fast and gun heavy ships leave the enemy trade convoys nowhere to hide.
Not only submarines can hunt.

Carrier Operations

Carrier: Organization +20
Naval targeting +10%

Carriers will allow our pilots to strike at sea faster and easier than from our airbases on land. We will strike before they have time to react.

Convoy Interdiction

Submarine:

Torpedo reveal chance −10%

Improved coordination of our submarines will let them strike at trade convoys en route. Disrupting the enemy's supply lines will give us the strategic advantage.

Capital Ship Raiders

Battlecruiser:

Battleship:

Enemy fleet size penalty +10%

With our most powerful ships on the hunt for trade convoys, the enemy will no longer find safety in numbers. They are sitting ducks praying we will not find them.

Convoy Sailing

Destroyer:

Sub detection +5%

Organization +10

Escort efficiency +5%

Introducing compulsory convoy sailing will make it easier to spot enemy raids and respond in time. Safety in numbers is the way to go.

Unrestricted Submarine Warfare

Submarine:

Surface detection +10%
Raiding efficiency +5%
Attack +10%

Let our submarines sink any vessel without warning, civilian or not. While some consider this a breach of the rules of war, there is no denying its effectiveness.