The Leviathan is a massive 
Illuminate ship resembling a Trilobite, introduced in the Heart of Democracy major update. Armed with 8 laser cannons and multiple Illuminate deployment rings, it parades throughout the skies, saturating the ground in lakes of expended plasma as it spreads destruction unimpeded.
Unlike other units in the game, Leviathans will only spawn in an operation with the "Leviathan Blockade" modifier in-place. Outside of this, they are not present elsewhere.
Appearance
A Helldiver watches a Leviathan flying through the streets of Remembrance during the Battle of Super Earth. Picture taken May 20th, 2185.
The Leviathan is a massive, multi-segmented ship, armed with a series of laser cannons in each of its fins, specifically 1 laser per fin for a total of 8. Similar to the armor worn by the Overseers, the Leviathan is covered in a thick, white material that can only be reliably penetrated by anti-tank weaponry. However, even with these weapons, the Leviathan can take extreme amounts of punishment and still continue firing. It can take up to 2 Planetary Defense Cannon shots or 4 SEAF SAM Site missiles to take it down.
Strohmann News footage of The Great Host shows the Leviathan flying through space alongside smaller Warp Ships and larger Overships, showing that the vessel is space-capable. Combined with their use as blockade ships, it is likely that Leviathans fulfill a similar role in the Illuminate Armada that the Super Destroyer does in the 
S.E.A.F. Navy.
Behavior
The Leviathan floats high above the battlefield, circling the area and knocking down any tall buildings it may happen to fly into. If it happens to fly over 
Helldivers or S.E.A.F. Troops, it will target them so long as they are within line of sight and a moderate distance. It can also deploy Illuminate Overseers to the ground.
Due to sheer power of the Leviathan's cannons, it is recommended to break line of sight with the ship to avoid taking damage, as even a single shot of its laser cannons will, if not instantly kill you, leave you ragdolled, with broken limbs and missing a critical portion of your health bar.
Tactics
- Leviathans have anti-tank level armor all-around. Nothing but the most powerful of support weapons will make a dent on their hulls. While the outer shell requires anti-tank weaponry to damage it however; the exposed innards can be damaged by heavy-armor piercing weaponry.
- Their plasma cannon turrets are also only heavy-armored.
- Leviathans will constantly spawn throughout the mission from the edge of the map. They will typically orbit around points of interest and objective locations, strafing ground targets with their plasma cannons like a ground-attack gunship. They do not actively follow Helldivers, but their area of operations are wide enough that eventually they're going to see them and engage. There is a set number of leviathans that may appear in the field at any time, and will not exceed this number, until one leaves.
- Leviathans will eventually leave the map after a certain amount of time. However, they will typically have a replacement deploy somewhere else. For this reason, it maybe best to simply disarm the leviathans turrets, then leave them to linger around the map, as this delays their reinforcement of a new fully-armed ship.
- The Leviathan has two forms of attacks.
- The first are its 4 head-mounted plasma cannon turrets. These are powerful and are capable of instantly killing a helldiver with a direct hit. They are able to independently target different enemies at the same time and have a 360-degree FoV, giving them unparalleled overwatch abilities. Previously invincible, the turrets can now be destroyed individually.
- The second are its plasma bombs, which are dropped from the holes in its wings. These will only be used against targets that are under the leviathan. They function similarly to the plasma cannons, except they are fired at a much higher rate. For this reason, it is ill-advised to go under a leviathan.
- Leviathans will now shine a bright spotlight onto their target, shortly before firing. This will alert a targeted Helldiver that they have a Leviathan's attention, and should find a way to either dodge incoming fire, or try and take it down.
- Leviathans cannot be stealthed like other superheavies like the Bile Titan or Factory Strider, even if one is concealed, crawling, and no other enemies are nearby: it will fire upon a helldiver upon entering it's effective range.
- Leviathan cannon turrets can now be destroyed, although they can only be damaged by heavy-penetration weaponry, and even then anti-tank weaponry is still recommended due to each turret's durability.
- Most anti-tank missile launchers can destroy a turret in one hit. The exception is the MLS-4X Commando, which requires two.
- The RS-422 Railgun can destroy each turret with 3 overcharged shots.
- The E/AT-12 Anti-Tank Emplacement can destroy each turret in two shots.
- If the two "fins" on the head are destroyed from a leviathan, all turrets in that section are also destroyed.
- The vertebrate and fins around each, will all expose a heavy-armored weakpoint once sufficiently damaged. Destroying 3 parts is typically enough to destroy a leviathan completely.
- This is best done with high damage weapons such as the Recoilless Rifle, Spear or Expendable Anti Tank. They are typically exposed within two direct hits.
- It typically takes 5-6 direct hits from a GR-8 Recoilless Rifle or FAF-14 Spear to take down one leviathan. An E/AT-12 Anti-Tank Emplacement takes 13-15 direct hits.
- The EAT-17 Expendable Anti-Tank, MLS-4X Commando, StA-X3 W.A.S.P. Launcher, and LAS-99 Quasar Cannon, are not optimal choices for bringing down leviathans due to their limited max DPS. Their best use is for breaking a leviathan's armor plating to make them vulnerable to heavy-pen weaponry.
- Both the missile and autocannon turrets can engage leviathans, although they typically have to be deployed within 100-150m of a leviathan. While not likely to destroy them on their own, they do soften it up for further attacks, thanks to their anti-tank penetration.
- The Orbital Defense Cannons used to destroy the Illuminate Overships, can also destroy a Leviathan in 2-3 direct hits, however properly aiming the cannon requires both a well coordinated team and good timing.
- It is possible to have an Eagle Strafing Run destroy a leviathan by having it strafe the length of the ship. However, this typically requires one to be infront of the ship to throw it infront and have Eagle-1 strafe it as the ship approaches. The DSS Eagle Storm though does not have this problem and is highly effective at shooting down Leviathans.
- It is technically possible to shoot down a leviathan with explosive-based Orbital Strikes. However, this requires one to compensate for their Super Destroyer's position, so that when the destroyer fires their shots, the trajectory will pass through the orbiting leviathan.
- Both the Orbital Railcannon Strike and Orbital Laser will track leviathans. But they must be placed below the craft itself, which exposes one to danger.
- If the leviathan passes through an elevated area of the city or one finds themselves on a rooftop with one nearby, it is possible to shoot one down with a GP-31 Ultimatum, with the aid of a hover pack. However, the conditions required to pull this off, does not make it practical.
- The B-100 Portable Hellbomb can destroy a leviathan utterly. However, they require very unconventional strategies to pull off.
- They are very slow-moving targets. Using cover is a great way to avoid conflict with them. If this is not possible due to terrain outside of colonies or cities, having offensive or defensive options against a leviathan may be the only way to survive an encounter.
- It is entirely possible to run through an entire mission, without shooting down any of the patrolling leviathans. This however, requires helldivers to be extra vigilant about patrolling leviathans and using the terrain to mask their movements to avoid getting gunned-down in the open. Simply ensure that there is either a roof or a building between you, and them.
- The husk of a Leviathan will kill anyone unfortunate enough to be crushed by it, once it crashes down onto the earth. It will also explode shortly after landing.
- The EXO-49 Emancipator Exosuit's autocannons can destroy Leviathans if aimed at the bottom of the ship, however it is not recommended to do this, as it takes up a whole magazine per cannon to accomplish this task.
- The FX-12 Shield Generator Relay provides a decent level of defense against Leviathans in the open, as it is capable of soaking over 9 direct hits before it fails, assuming one is not under heavy fire from other sources. And it will typically block a few more shots when it recharges.
- Two or more helldivers with a Shield Gen Relay stratagem can increase their survivability during defensive actions by throwing shield generators in sequences as each one expires.
- The portable SH-32 Shield Generator only has enough durability to withstand one direct hit. It is not a reliable defense, but may save one's life in a pinch.
- Orbital and Eagle Smoke stratagems will typically cause leviathans to break visual contact with a helldiver once inside the smoke screen. However, this may not be as ideal if multiple leviathans are around, as there is a chance one of them will still see through the smoke if they are orbiting from from various angles. And whether due to another bug, or host-connection issues, they will see through the smoke regardless.
Trivia
- The Leviathan appears to be a living creature. When their head weakpoint is destroyed, organic-looking appendages can be seen jutting out of it, rather than the hull cracking or it catching fire. Additionally, rather than mechanical sounds, it appears to wince in pain whenever its weakpoints are destroyed, or it is killed. Additionally, when it dies, blue fluid similar to Illuminate blood will burst from the Leviathan, further suggesting that it is alive.
- Visually, the Illuminate Leviathan shares many of the same features as the Chitauri Leviathans from The Avengers (2012), as well as the T'au Merchant Fleet from Warhammer 40k; more-so the former rather than the latter if it is indeed a living creature.
