Quick answer: A Calamity Tower in Once Human's Isles of Abyss is a sea-fortress boss you fight from your ship. You beat it by clearing the tentacles around it, then focus-firing the weakspot whenever it's exposed. Tentacles each have a job: blocking an area, summoning reinforcements, healing, or sharing damage. Kill the healing and damage-sharing ones first, and use ship cannons on tentacles shielded by building protection, because small arms barely touch them. Towers start as solo story challenges, become team fights, and open a harder Calamity Tower: Abyss version in Phase II. The land-based Calamity Nest is a different fight against the Calamity Owl. If the Owl looks immune, it's in a shield or flight phase, and you break that with the arena mechanics (feathers, floating energy orbs, the Revenge mark). Shooting harder won't do it. Everything below is current for Version 3.1.1 (October 21, 2026 PT / October 22 global).
Isles of Abyss has only been live for about a day, and the questions in the community are the obvious ones: why can't I damage this tower, why is the owl immune, and where's the reward chest? Most of the guides already out there cover the scenario in general, not these fights. This one is built from the studio's own Isles of Abyss dev blog and the 3.1.1 update notes on oncehuman.game, plus what players are reporting from the first servers.
What is a Calamity Tower in Once Human?
The Calamity Tower is one of the main challenge types in the new PvE ocean scenario, along with Voyagers, Calamity Nests, Sea Calamity Zones and the endgame Sunken Lord. The studio describes it as a three-stage progression:
"From solo challenges that progress with the main story, to team battles, and then to the abyss challenge in Phase II, the Calamity Tower will progressively test your ship cannon handling, ship maneuvering, and cooperate skills." (Once Human, Version 3.1.1 Update Announcement, Oct 21, 2026)
So it isn't one fight. It's a ladder:
| Stage | When | Who | What it's for |
|---|---|---|---|
| Story Calamity Towers | Phase I, as you progress the main story | Solo | Unlock gear crafting steps tied to the story |
| Team Calamity Towers | Phase I onward | Group | Harder versions built around tentacle roles and focus fire |
| Calamity Tower: Abyss | Phase II, after the prerequisite challenges | Group | The hardest version: stacking tentacle abilities, attacking cores, Voyager reinforcements |
The official 3.1.1 notes say plainly that "completing challenges in the main story will advance the unlock of corresponding gear craft". In other words, story towers aren't optional. If your crafting tiers stall, a tower you skipped is the likely reason.
Towers also gate the map. Starry Studio's launch press release says a tower guards each region, and toppling it unlocks "higher crafting tiers and the next region" (Starry Studio launch release, Oct 2026). They matter beyond your own character too. In the earlier Pioneer Test preview, the studio said Calamity Towers activate as your server's World Progress advances, and that the first time a server defeats one, the whole server gets a reward mail and extra World Progress. Faster tower clears mean an earlier Phase II: per the official dev blog, Phase I lasts about 5–10 days and gets shorter as the server's purification progress advances, and Phase II then runs 11 days. Treat the Pioneer Test detail as a preview, because the launch dev blog doesn't restate it.
How do you beat a Calamity Tower?
Every Calamity Tower fight follows the same loop. The studio sums it up in one line: "Combat revolves around tentacles and weakspots: clear outer threats and seize the moment when weakspots are exposed to focus fire." This is how that plays out.
1. Read the tentacles before you shoot. Each tentacle has one of four roles, per the official notes:
| Tentacle role | What it does | What to do |
|---|---|---|
| Area block | Seals off part of the water around the tower | Our call: reposition rather than spend ammo on it, unless it traps you |
| Reinforcements | Summons extra enemies | Our call: kill it early in solo runs, before the adds stack up |
| Healing | Restores the tower or other tentacles | Our call: priority 1, because it undoes your damage |
| DMG sharing | Spreads damage across the group | Our call: priority 1–2, because hits on the core lose value while it's up |
The official wording is that "handling support objectives in time and assigning firepower is the key to a team's breach". In a group, assign one gunner to support tentacles and keep everyone else on the main target.
2. Use ship cannons on protected tentacles. "Some tentacles are protected by building protection, and the destructive power of ship cannons will come into play here." If your rifle is barely denting a tentacle, it's probably protected. Swap to a deck cannon.
3. Burst the weakspot when it opens. The weakspot isn't always exposed. Clear the outer threats, wait for the opening, then have everyone on the ship fire at once. Rotating one by one wastes the window.
4. Keep the ship moving. Ship maneuvering is one of the three skills the tower tests. A stationary ship gives the tower and its adds a free target, and in Phase II "waves, heavy fog, Icebergs, and water tornadoes" also push you around (more on that below).
5. Open the reward stage before you sail off. Towers end with a reward stage. One player's tip after day one is literally "Don't forget the chest at the end of defeating the calamity towers!" (r/OnceHumanOfficial) At least one reply admitted nearly sailing away without it. This is also where your Heart of the Ocean gets spent (see the rewards section).
Which ship cannons should you bring to a Calamity Tower?
Ship cannons unlock with Tech as the scenario goes on, and you switch between equipped cannons with the weapon wheel while you sail. Cannons with projectile drop get a pre-aim line, which helps a lot on controller. From the official cannon list, these are the ones that matter against a tower:
| Cannon | Official description | Tower use |
|---|---|---|
| Rapid-fire Cannon | Lower damage per shot than the Long Cannon, but shorter firing intervals and faster projectiles, "making it easier to aim at the weakspots of the Calamity Tower" | Best weakspot gun. The studio names it for this job |
| Long Cannon | Traditional artillery; "deals Additional DMG to decks and other buildings" | Building-protected tentacles and structures |
| Repeating Long Cannon | Continuous fire | Sustained damage while the weakspot is open |
| Corrosion Cannon | "Increases the damage enemies receive" | Debuff before a team burst |
| Frost Cannon | Slows targets | Controlling adds and chasing fast enemies |
| Harpoon Cannon | Fast projectiles that penetrate the water surface | Marine creatures, not the tower itself |
| Shotgun Turret | Wide volley | Enemy ships and patrol boats, e.g. Voyager reinforcements |
Phase II adds four more cannons: the Rocket Launcher (burst of small projectiles, "considerable sustained output"), the Oil Drum Launcher (big explosion that ignites the area), the Repeating Shotgun Turret ("extremely high damage to Voyagers") and the Freezing Cannon (freezes targets). For Calamity Tower: Abyss, that means one Rocket Launcher or Rapid-fire Cannon on the weakspot, plus a Shotgun-type turret for the Voyager reinforcements that show up in that version.
Two more ship tools are worth knowing. The Ram handles close-range collisions, and the Naval Mine Launcher sets traps. A Giant Squid can latch onto your hull mid-fight and hold the ship in place until you sever its tentacles, so keep a Harpoon Cannon mounted if you fight towers in open water.
Don't skip ship durability. The official ship kit includes the Time-Reverse Welding Torch for repairing buildings and facilities, and a territory repair facility that keeps repairing damaged material once it's switched on. Your ship counts as movable water territory, so set that up before a team tower, not after.
What changes in Calamity Tower: Abyss (Phase II)?
Once your server reaches Phase II (an 11-day phase in the official cycle) and you've completed the prerequisite challenges, you can go deeper into Calamity Tower: Abyss. The official notes list what gets harder:
- Tentacle abilities stack and intensify. The four roles stay the same, but you'll see more of them at once.
- Cores launch active attacks. In Phase I the weakspot mostly waits for you. In Abyss it fights back.
- Voyager reinforcements join the battlefield. You're fighting enemy ships and the tower at the same time.
- Waves, heavy fog, Icebergs and water tornadoes affect your route. Heavy fog cuts your view of the weakspot, much like the Mist of Deceit (see our Haywire Zones guide).
The studio's advice is to "find windows of opportunity to attack while dodging dangers, and breach the defenses together with your companions." Our recommendation: one driver who does nothing but steer, and two or three gunners. Solo Abyss runs aren't what this content was designed for.
How do you beat the Calamity Owl in a Calamity Nest?
The Calamity Nest is the land version: a stronghold on an island with the Calamity Owl as its alpha. You can fight it solo or in a team. According to the official notes, the Owl "will summon enemies with its song, applying constant pressure with sound waves and area attacks". The fight is about balancing add-clearing against damage on the Owl.
Three mechanics decide the fight:
The Revenge mark. During combat the Owl marks one player. "The marked Meta becomes the enemy's pursuit target while also gaining a key opportunity to attack the alpha." The marked player gets chased, but they're also the one who can punish the Owl. Everyone else should peel adds off that player and keep them alive.
Feathers. On some difficulties the fight "extends from the ground into the air". Pick up fallen feathers for a short lift-off so you can reach it.
Floating energy orbs. Touching them counters the Owl. This is the mechanic most "the owl is immune" posts are missing.
Why is the Calamity Owl immune?
This is the most common Calamity Nest question from launch day. One player wrote on r/OnceHumanOfficial that every time they arrived, the fight had already started and "the owl is immune". They couldn't see any orbs or feathers, and searching didn't help. The only reply so far (a player report, not official) described two separate states:
- A big spherical shield: a player reported destroying two yellow crystals to drop it.
- Around half health, "windy balls" spawn: these line up with the official floating energy orbs. The same player said they wait out that phase when they can't reach them. That's a valid fallback if you have no feathers.
The crystal detail comes from players, not the studio. The official notes only mention feathers, orbs and the Revenge mark. Still, it lines up with how the rest of Isles of Abyss works: shields come off when you destroy a support structure, not when you deal more damage. The same rule shows up in Sea Calamity Zones, where you "destroy the shield core in the outer buildings to remove the central shield."
If you join a Nest mid-fight, you may have missed the feather or orb spawn. Clear adds, protect whoever has the Revenge mark, and wait for the next mechanic window before you spend ammo on the Owl.
Calamity Tower vs Calamity Nest vs Calamity Zone: what's the difference?
There are several "Calamity" names in the scenario, and they get mixed up in chat:
| Name | Where | Phase | Win condition |
|---|---|---|---|
| Calamity Tower | Sea | Phase I (story + team), Phase II (Abyss) | Clear tentacles, burst the weakspot |
| Calamity Nest | Land (islands) | From landing on the archipelago | Defeat the Calamity Owl using feathers, orbs and Revenge |
| Sea Calamity Zone | Sea | Phase II | Break the turret/mine defences, destroy the outer shield core, kill the Calamity Hatchling |
| The Sunken Lord | Underwater entrance platform | Phase II, at 100% server purification | Final co-op raid; the launch release calls it four-player (see our Sunken Lord guide) |
| Chaos Tower | Listed separately in the 3.1.1 notes | Not specified | Not part of the Calamity ladder; it's where the new Chaos Deviation Chaos Rebecca drops |
What rewards do Calamity Towers give?
Towers are one of the main sources of advanced rewards in the scenario. The official dev blog groups them with Voyagers: "challenges such as the Voyager and Calamity Tower offer advanced rewards." Here's what's confirmed:
- Gear crafting unlocks from the story towers.
- Heart of the Ocean is the scenario-exclusive advanced resource. Its main use is "to open challenge rewards". Spend it during the reward stage of a Calamity Tower (or the Sunken Lord) for a chance at the scenario's two new armor Mods: Precision Load (Lower Body; bullet recovery after a long-range weakspot hit) and Turret Enhancement (Gloves; more damage from facilities you use). Turret Enhancement is the obvious pick for a cannon-heavy tower build.
- Morphed Deviations: the 3.1.1 notes list Shattered Maiden - Sailor Suit and Gingerbread House - Oceanic Cottage from the Calamity Tower, and Snow Globe - Sunken Treasure from the Calamity Nest. They're a chance drop, not guaranteed, and the studio hasn't published odds.
- Server progress: first clears feed your server's World Progress, according to the Pioneer Test preview.
One warning from the in-game tooltip shown in the dev blog: "Realm-exclusive items cannot be taken out after the scenario ends." Spend your Heart of the Ocean during the run. Don't sit on it waiting for settlement, because Isles of Abyss is a ~21-day cycle and the permanent server is only expected around November 18, 2026 (PT).
How do you fight Calamity Towers on PS5 and Xbox?
Isles of Abyss is fully crossplay, so console crews will be in the same tower fights as PC players. A few controller-specific notes:
- Use the pre-aim line. Drop-arc cannons show one, so line the arc up on the weakspot before it opens instead of flicking onto it.
- Try the new Sensitivity Presets. 3.1.1 added Sensitivity Presets and a reworked sensitivity and vibration menu for controller. If you're overshooting weakspots, try a lower preset.
- Switch cannons from the wheel, not by walking to a different turret. Switch to the Rapid-fire Cannon before the weakspot opens.
- Party up first. Squads signed up together are guaranteed the same Isles of Abyss server. On Xbox you can invite through the console friend list. The studio says the PS5 version of that invite is still in development. Full steps are in our Isles of Abyss join guide.
For the ship itself (hull layout, propulsion tiers, saving the design), see our Isles of Abyss shipbuilding guide.
FAQ
Can you solo a Calamity Tower in Once Human? Yes. The story Calamity Towers are solo challenges tied to the main story. The team versions and Calamity Tower: Abyss in Phase II are built for groups, with tentacle roles you need to split fire across.
Why can't I damage the Calamity Tower tentacles? Some tentacles have building protection. The studio says this is where "the destructive power of ship cannons will come into play". Switch to a deck cannon such as the Long Cannon, which does extra damage to buildings.
What is the best cannon for Calamity Tower weakspots? The Rapid-fire Cannon. The official notes say its faster firing and projectile speed make it "easier to aim at the weakspots of the Calamity Tower." In Phase II, the Rocket Launcher adds strong sustained damage.
Why is the Calamity Owl immune? It's usually in a mechanic phase. Players report a spherical shield that drops when two yellow crystals are destroyed, and an energy-orb phase around half health. The official notes say touching the floating energy orbs counters the Owl, and fallen feathers let you reach it in the air.
Where is the chest after a Calamity Tower? It's at the end of the fight. That's the tower's reward stage, where you can also spend Heart of the Ocean for a chance at the new Precision Load and Turret Enhancement Mods. Players on day one report nearly sailing away without opening it.
Does Heart of the Ocean carry over after Isles of Abyss ends? No. The in-game tooltip says realm-exclusive items cannot be taken out after the scenario ends, so spend it during the run.
More Once Human guides
Sailing into Isles of Abyss this week? Our console-first Once Human guides cover the new scenario, its systems and every launch error.
