The Construction Ship is a good builder in terms of build power and speed. Even a single one of these assisting the lab almost doubles its output of units provided that you have the resources. On top of Commander’s build list they're able to produce more advanced T1 defences like the Floating Heavy Laser Turret and give access to T2 Shipyard. It adds 50 to your metal and energy storage capability 

Use them for assisting the lab and quickly expanding, claiming the metal spots with underwater metal extractors.

Death Cavalry is a stealthy resurrection submarine. They are not visible to the units on the surface, if your enemy doesn’t have a sonar nearby, hence they can be used as a precious support to your feet, providing repairs, reclaiming and resurrecting wrecks. They have much higher build power and costs than their land counterpart, therefore you don’t need many of these. Two or three are usually enough to bring a big wreckfield back to life in reasonable time. 

Enforcer is the heaviest of T1 ships. It’s biggest advantage is its durable armor and versatility. They are equipped with a powerful long range plasma cannon and a depth charge launcher. Their range allows them to outrange all ships and also torpedo static launchers, which makes them a great choice for pushing the front-line. They are also used as a good counter to submarines. However, due to slow movement and low maneuverability, they can get easily overrun by lighter ships.

It is a good idea to provide them with an escort of lighter ships and repairing support. They are costly and leave very precious wrecks, so take good care of them!

Enforcers have a higher cost, but also higher damage compared to their ARMADA counterpart (Crusader)

Envoy is a heavy and durable sea transporter. Each one has a transport capacity of 40, with each unit carried taking up space: 4 spaces for a large unit, 2 for a medium unit, and 1 for a small unit. They are mainly used to quickly transport the Commander and land constructors across water. The Commander can be loaded or unloaded from underwater. 

Their armour is able to withstand a lot of damage, therefore it is pretty safe to move Commander this way. Though when the transporter gets destroyed all units inside go down with it as well. It can unload and pick up the Commander from underwater.

Era is an assault frigate equipped with two light plasma cannons with decent range. It resides in the middle-ground between corvettes and destroyers. It’s main use case is defending from Destroyers, as its range and speed allows it to outmaneuver them and deal some significant damage, though you need to make in big numbers to pull that off. 

Costwise, you can make two of these for every destroyer, so it is a good investment for fighting against them. However, they get easily countered by submarines, against which they have no weapon.

Eras have a higher cost, but stronger armor and weapons then their ARMADA counterpart (Ellysaw).

Searcher is a light scout/AA ship, offering very high speed, and a big line of sight. Use them in the beginning of sea battles in order to harass enemy’s early base structures and block constructors from expanding. 

Their AA turret is weak and won’t stand a chance versus more advanced aircrafts but during the T1 stage it proves very useful to protect your ships from EMP drones and gunships. Always include a bunch of these in your fleet.

They are hopeless in a matchup with any other ships, hence only use them as a support/scouting force. 

Searchers are a bit slower than their ARMADA counterpart (Skeeter).  

Snake is a stealthy assault submarine. They are equipped with powerful torpedo launchers that can deal some lethal damage to structures and ships within seconds, though they are also very vulnerable due to low health. They are kind of a glass cannon. 

Snakes are invisible to radars and the units on the surface, so if your enemy is not careful enough you can sneak one or two of these into his base and cause some havoc. 

The main use case for those is taking down underwater metal extractors and trapping fleets, which don’t include proper anti-submarine units, like Destroyers. 

Supporter is a fast and very maneuverable light assault ship. They are equipped with two rapid-fire short-range laser turrets. Useful for raiding the expanding constructors in the early-mid T1 stage. In higher numbers they can overpower heavier ships if your enemy doesn’t carefully micro them. Similarly to AK’s on land, corvettes pack a relatively high DPS, but only in close distance.  

Tip: try to keep their broadside facing the enemy unit while attacking, to maximize damage. Turrets are not able to shoot over each other, so only one will be used when facing the enemy head-on. 

Similar to the Peewee/AK matchup, Supporters have lower damage but higher accuracy than their ARMADA counterpart (Decade).

Advanced Construction Sub is the T2 sea constructor. Their typical first tasks are upgrading your metal extractors, building fusion reactors and then advanced metal makers.

They have a higher build power than the T1 Construction Ship and grant a small boost to both your metal and energy storage. Guard them with other constructors or naval engineers to assist with building.

In addition to T2 economy structures, they are able to build advanced torpedo launchers and the underwater experimental gantry.

Black Hydra is the CORTEX flagship. They are the most powerful ships and arguably the most powerful units available. They combine awesome fire power with exceedingly long range. Construct one of these and watch as your enemy fleet pales into insignificance.

They are equipped with two plasma cannon turrets, laser turrets and even a small anti-air missile launcher. Their main cannon range exceeds even that of the missile cruisers and possess such might that plasma shields will provide only a temporary respite from the shells.

While the cannons obliterate targets from afar the lasers give the Black Hydra incredible lethality at shorter ranges too. Owing to the range and mobility a Black Hydra is able to destroy any T3 unit they clash with, as long as it doesn't get too close.

They achieve maximum damage when oriented to their targets from the broadside, so they are able to shoot all cannons and lasers at once.

While they are also equipped with medium anti-air missile launchers they are still vulnerable to heavier aircraft and possess no anti-submarine weaponry so never leave them bereft of an escort.

Executioner is a medium assault cruiser. Positioned as an upgraded version of Destroyers and a frequent part of any T2 naval group. Wielding a medium-range plasma cannon, a pair of light laser turrets and a depth charge launcher the cruiser is a flexible vessel. They are the fastest T2 ship and useful for rushing your opponent in the initial T2 naval warfare phase. They can easily take out any T1 units while also offering protection against both hovercraft and submarines.

Hive is both an aircraft carrier and a mobile anti-nuke system. They can be used to repair damaged aircraft but their main use is to protect against nuclear missiles. They are equipped with both medium range radar and sonar to help your fleet spot enemy units. The anti-nuke interception range is lower than anti-nuke structures; but they are the only possibility in protecting the sea from nuclear strikes.

Leviathan is a battle submarine. They have both unmatched damage and range. The threat they pose to unguarded fleets is not to be underestimated and their ability to deal damage at range makes them truly dangerous. While devastating in the correct circumstances the Leviathan is vulnerable to both submarine killers and torpedo launchers.

The ideal use of them is to destroy heavy ships and protect the sea from T3 amphibious units. Utilize their range and try to keep a good safe distance. 

Messenger is a missile cruiser. They are equipped with a heavy long-range missile launcher and a medium anti-air missile turret. Their focus is typically to get to the shore of an enemy and unleash an overwhelming first strike against their defences. A few missiles will completely level most structures and their range exceeds all land-based defence structures, even Annihilators, so the only realistic way to counteract them is to intercept them or hit them with tactical nukes.

A high missile trajectory enables them to shoot over mountains and other natural land barriers, which can stop other ships that use plasma cannons. As their munitions are not plasma based they will also completely ignore plasma shields.

Take advantage of the element of surprise by combining them with jammer ships to hide them from enemy radar, and let them sneak in close enough before starting the bombardment.

Pathfinder is a naval engineer. Similar to Freakers on land, these are used to assist T2 constructors and to quickly build T1 units in the field. Notably, they can build Floating Nano Turrets, plant powerful naval mines and produce T1 combat units such as Enforcers, and Supporters.

Never underestimate the destruction a carefully positioned minefield can bring about. With them you can rapidly secure large areas. Mines are effective until you are able to produce the more powerful T2 ships to fend off hovercraft assaults.

Phantom is a radar jammer ship, allied units nearby vanish from enemy radar. While bereft of armaments the Phantom plays a vital role in keeping your ships from the enemy radar screens. But beware, the Phantom will not stop the enemy spotting your ships visually and line of sight will make the Phantom ineffective.

Combining a cloaked unit with a jammer makes a given unit totally invisible.

Place one amongst a group of missile cruisers. While undetected they can maneuver around the enemy flanks and bring about terrible damage to the foe. Once the attack is complete they can escape out of sight and become difficult to hunt down.

Shark is a submarine killer. It is ideal for obliterating enemy submarines, in particular the T2 battle submarines. Sharks deal additional damage to submarines, move more swiftly, turn faster and have a better angle of fire compared to other submarines. These attributes give the Shark unmatched lethality against battle submarines which against an unguarded fleet would cause devastation..

Always include a few of these in your T2 navy.

Shredder is an anti-air ship. Wielding a mighty flak cannon and light missile launcher the Shredder is capable of obliterating entire waves of enemy aircraft. Light aircraft disintegrate like confetti and even heavier aircraft fall from the sky under the hail of fire from the Shredder.

Include at least one of these in their fleets to help destroy the enemy even when in the skies.

Warlord is a heavy battleship. They are equipped with a powerful long-range plasma cannon and heavy laser. They are masters of ship to ship warfare; sinking enemy ships with ease and even taking the fight to land based targets.  

While their heavy armour makes them a difficult target to take down for most foes, Battle submarines are the natural enemy of the Warlord as it cannot target the underwater vessel and will take significant damage from it.