Hearts of Iron 4 (HOI4) – Navy Guide

While most gamers often focus on land battles, naval warfare in Hearts of Iron 4 plays a crucial role. Mastering naval strategies is essential to defeating powerful nations like the United Kingdom and Japan.

Despite many players winning World War 2 multiple times, understanding naval mechanics remains a challenge due to frequent updates altering gameplay dynamics.

Thankfully, recent updates have stabilized naval strategies, making it easier to implement consistent winning tactics regardless of the country you choose.

In this comprehensive guide, we will delve into all aspects of navies in Hearts of Iron 4, including naval research, combat, ship types, fleet setup, doctrines, and how to emerge victorious in every naval battle.

Table of Contents

Before delving into naval strategies, understanding Naval Research is crucial in Hearts of Iron 4. The research tree introduces various hulls, which serve as the foundation of ship design.

Researching hulls unlocks a key piece of the puzzle, allowing you to enhance speed, reliability, and range while increasing production costs. Depth Charges under Destroyer hulls aid in combating submarines, essential for protecting convoys.

Cruiser hulls offer armor upgrades, with caution advised due to speed debuffs outweighing benefits. Submarine upgrades around 1940 lower sub visibility, a critical enhancement for submarine warfare.

Naval Support research enhances ship capabilities and streamlines naval combat efficiency. Armaments provide ship guns, vital for maximizing combat effectiveness. Torpedoes offer critical damage to Battleships and Carriers, while Fire Control tech boosts fleet attack stats.

Transports are essential for naval invasions, with Mine Warfare upgrades focusing on mine damage improvements. Prioritize main line upgrades instead of minelaying options for efficient fleet management.

How Does Naval Combat Work in HOI4?

Naval combat in Hearts of Iron 4 differs from land battles in frequency and scale. Confrontations between fleets often result in significant losses for one side, emphasizing strategic planning and preparation.

Engagements typically focus on destroying convoys or safeguarding troops during naval landings. When fleets clash, ships position themselves in four lines – Screening Group, Battleline, Carrier Group, and Submarine Wolfpack.

Battles unfold as ships maneuver based on speed and reconnaissance, engaging in combat until one side decides to retreat, often resulting in heavy losses for the defeated fleet.


Screens, comprising Destroyers and Light Cruisers, serve as frontline defenders against enemy fire. Their speed and resilience protect heavier ships, acting as shields for the entire fleet. High Screening Efficiency reduces torpedo threats to backline ships.

Deploying adequate screens ensures fleet protection, with Destroyers absorbing damage while Light Cruisers engage enemy screens. Screens play a pivotal role in fleet defense and strategy.


The Battleline, positioned behind Screens, focuses on dealing damage. Battleships and Heavy Cruisers form the Battleline, equipped to inflict substantial harm on enemy Screens and Battlelines. Vulnerable to torpedoes, Battleline ships rely on Screens for defense.


Carriers, part of the Carrier Group, operate at a distance from the main battle, launching airstrikes while staying clear of direct combat. Protected by Screens and Battleline, Carriers target enemy ships with bombers for maximum impact.


Submarines operate independently below other lines, vulnerable to Depth Charges when detected. Securing visibility advantage over Submarines is crucial for effective anti-submarine warfare.

How to Set Up a Fleet

The optimal fleet configuration in HOI4 involves consolidating all ships into a single expansive task force. While specialized fleets have merits, a unified fleet offers superior firepower and survivability in decisive battles.

Deploying a single formidable fleet minimizes vulnerability to surprise attacks by enemy forces, ensuring fleet integrity and combat effectiveness.

Specialized fleet configurations, such as convoy raiders or minelayers, can complement the main fleet for strategic advantages in specific regions or operations.

Utilize the Strike Force command for the main fleet, ensuring prompt engagement and naval supremacy in contested regions. Refrain from deleting ships, as every vessel contributes to overall fleet strength and battle outcomes.

Hearts of Iron 4 offers three naval doctrines for strategic customization:

  • Fleet in Being
  • Trade Interdiction
  • Base Strike

The Fleet in Being doctrine enhances battle efficiency, making ships more effective in combat engagements. Choose this doctrine by default for optimal performance in naval warfare.

Trade Interdiction doctrine focuses on disrupting enemy supply lines and convoys, ideal for minor nations lacking significant naval power. Avoid the Base Strike doctrine, prioritizing other doctrine options for better combat outcomes.

How to Always Win Naval Battles

To ensure victory in naval battles, consolidate ships into a formidable fleet and prioritize the Fleet in Being doctrine for enhanced combat capabilities. Nations with strong navies like the UK, US, and Japan benefit from producing Destroyers and Light Cruisers to maintain fleet efficiency.

Strategically position fleets in key naval regions on Strike Force command to establish naval supremacy and deter enemy incursions. Conduct patrols with destroyers for reconnaissance, enabling the main fleet to engage decisively when enemy fleets are located.

While naval battles are unpredictable, focus on achieving capitulation through naval invasions or defensive strategies. Emphasize securing objectives without engaging in unnecessary battles, leveraging fleet strength to maintain superiority.

Explore all facets of naval warfare in Hearts of Iron 4, from research to combat strategies, to dominate the seas!

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