Why won't my naval invasion launch in HOI4?

Check, in order, naval supremacy (over 50% in every region crossed), free convoys , the order's capacity (4 divisions at the start) and whether preparation has finished. Naval intel efficiency below 40% also reduces your supremacy.

How many divisions can land at once?

An invasion order takes 4 divisions without technology. Naval transport research raises that cap and the number of simultaneous plans. Above the limit, the order shows zero transports and never launches.

Do you need a DLC for naval invasions?

No, naval invasions are part of the base game. The Floating Harbor requires No Step Back, and the marine sub-doctrines of special forces are tied to Arms Against Tyranny according to the Paradox dev diary.

What should you do after landing to avoid losing your divisions?

Take a port as fast as possible: without a port or a Floating Harbor, landed divisions are cut off from supply. Keep the fleet on invasion support and send reinforcements to the beachhead before the counterattack.

HOI4: how to do a naval invasion (patch 1.19.4)

A naval invasion in Hearts of Iron IV launches when five conditions are met: a departure port, enough convoys, enough invasion capacity, finished preparation and over 50% naval supremacy in every sea region crossed. For patch 1.19.4 of October 27, 2026, the procedure comes down to four steps:

Select an army and pick the naval invasion order.
Click a departure port, then right-click the target coastal province.
Wait for preparation to finish, with a fleet on naval invasion support.
Launch as soon as the arrow turns green, then go for an enemy port.

The mechanic is part of the base game. The Floating Harbor requires the No Step Back DLC, and the marine sub-doctrines depend on Arms Against Tyranny.

The five conditions to check before launching

The official wiki and the Guild Order guide list the same locks. The game does not present them in order: the invasion arrow only tells you something is missing.

A departure port. A province with a naval base, yours or one belonging to an ally not at war with the target.
Free convoys. Each division uses them according to its weight, rounded up. An armored division needs far more than light infantry.
Order capacity. It starts at 4 divisions per order and 1 simultaneous plan. Naval transport technologies raise both.
Preparation. It must reach 100% before launch.
Naval supremacy. Over 50% in every sea region along the route, not just off the beach.

If you assign more divisions than the capacity, the order shows zero transports and the divisions keep their red exclamation mark. This is the most common beginner mistake. What matters is reading the transport count before blaming the fleet.

Naval supremacy: the real lock

Supremacy is measured per sea region. It adds up the contribution of your fleets present there, weighted by their mission. The guides-factory navy guide uses the wiki’s coefficients:

Mission	Share of supremacy counted
Strike force or invasion support	100%
Patrol	75%
Convoy escort	50%
Convoy raiding, minelaying or minesweeping	25%
Naval exercises or hold	0%

A fleet set to do not engage counts for nothing. Air superiority adds up to +100%: in a zone where you own the sky, every ship counts twice.

Naval intel matters as much as the fleet. Below 40% naval intel efficiency against the enemy, your supremacy is reduced; at 10% or less, it is halved. In practice, a spy network, coastal radar and recent naval battles help you clear that threshold.

On paper, supremacy is only checked at launch: once the 100% preparation bar turns into a moving fleet, the invasion proceeds even if the enemy fleet comes back. The risk is elsewhere. Raiders hitting your convoys during the crossing heavily delay the landing, and a delayed landing gives the defender days to move reserves to the beach.

Preparation: why it takes months

With early technology, count about 7 days per division: 1 division needs 7 days of preparation, 10 divisions need 70 days. Naval transport technologies cut that delay. Preparation advances while divisions travel to the port, so assign the order before they even arrive.

Planning bonus, however, barely rises for an invasion: the game applies a heavy penalty to its build-up. In practice, waiting longer after 100% gains nothing. Launch as soon as preparation is complete.

What matters for timing is the calendar of the war, not the bar itself. A 10-division plan started in January 1940 only reaches 100% around mid-March with early technology, so plan the invasion before the target theatre becomes urgent. The risk of starting late is landing when the enemy already has divisions free to counterattack.

Several invasions can prepare in parallel from different ports, up to your simultaneous plan limit. This is the safest way to land a large army: three 4-division orders on three nearby beaches rather than one giant order.

Holding the beachhead: ports and the Floating Harbor

A successful landing is only half the job. Without a captured port or coastal city, your divisions are cut off from supply and draw on their reserves. The priority target after the beach is the nearest port. Pick the beach based on that port, not on how weak the defence looks.

The Floating Harbor, added with No Step Back, solves this problem for a while. The supply dev diary describes it as an artificial harbor inspired by the Battle of Normandy. It works in three steps.

Production. It unlocks through research, then is produced in naval dockyards like a ship.
Order. You need one in stock and must pick the naval invasion order with Floating Harbor support.
Effect. It is consumed at launch and immediately creates a stocked supply hub at the landing site.

That hub is temporary. Paradox speaks of a few weeks to a few months depending on enemy air superiority; a Gamer Empire guide puts it at 30 days. The Floating Harbor buys time, but it does not replace taking a real port.

Which divisions to send

Divisions landing against resistance suffer an attack penalty. Marines, engineers, amphibious vehicles and flame tanks handle it better, according to the wiki; heavy equipment handles it worse. If you play a low-industry nation, a good first wave combines marines and engineers, with armor in the second wave once the port has fallen.

On width, a naval invasion adds an attack direction to the battle. Our division templates guide recommends 20 to 25 width to leave room for reinforcements on the beachhead.

Since patch 1.19.0, special forces have moved to the new doctrine system. The Paradox dev diary states that marine sub-doctrines, including Marine Commandos, are tied to Arms Against Tyranny. Patch 1.19.4 also strengthens amphibious tanks: their HP now depends on reliability, going from 2 to 3.5 at 100% reliability or more.

Why your naval invasion will not launch

When the arrow stays red, hover over it: the tooltip shows the missing condition. The causes always come back in the same order.

Not enough supremacy along the route. A single region crossed below 50% is enough to block it. Switch fleets to strike force or invasion support rather than patrol.
Naval intel too low. Below 40%, your fleet counts for less than it seems.
Not enough convoys. Convoys also serve trade and overseas supply; build more before launching.
Too many divisions in the order. Remove some until you are back under capacity.
Preparation incomplete. It must reach 100%.

Patch 1.19.4 adds a handy shortcut to start over: Alt+Delete removes every airborne and naval invasion order from the selected divisions.

Defending against a naval invasion

Since patch 1.19.0, the AI is more willing to try advantageous naval invasions, according to the anniversary update diary. For an exposed coast, the area defense order lets garrison divisions guard ports and coastline. Keep a few mobile divisions in reserve near the main ports: the invader has to take one, so that is where to wait.

In practice, the defender also benefits from geography. A coast with few ports forces the attacker to commit to one target, so a single well-placed division with engineers can hold long enough for reinforcements. Coastal forts on the main ports make this even harder, since the attacker cannot rely on the Floating Harbor forever.

The best defence is still at sea. A fleet that contests supremacy, or submarines raiding convoys, delay or block the invasion before it even reaches the beach.