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Locationmajor

Submersible

The Submersible is a small, mission-critical location in Baldur’s Gate 3, found beneath Flymm Cargo in the Lower City during Act Three.

Importancemajor

Key takeaways

  • The Submersible is reached through the basement and dock area beneath Flymm Cargo in the Lower City.
  • It is the only way to reach the Iron Throne.
  • Boarding it begins a one-way mission transition You cannot fast-travel or return to camp while the Iron Throne sequence is unresolved.
  • The time limit begins only after a party member leaves the Submersible and enters the Iron Throne.
  • The Submersible itself is safe ground before and after the prison sequence.
  • Once you disembark after returning from the Iron Throne, you cannot return to the Submersible or the prison.
  • Destroying the Steel Watch Foundry before visiting the Iron Throne can make the prison unreachable.
  • Rescued Gondians gather inside the Submersible after the prison mission, allowing the party to speak with survivors before leaving.

About this guide

Spoiler warning: This guide covers Act Three, the Iron Throne prison, the Gondian rescue storyline, Duke Ravengard, Omeluum, Redhammer and several irreversible progression consequences.

Overview

The Submersible is a small, mission-critical location in Baldur’s Gate 3, found beneath Flymm Cargo in the Lower City during Act Three. It is a transport vessel and temporary safe area rather than a full exploration zone. Its purpose is to carry the party to the underwater prison known as the Iron Throne, then provide a return point for rescued prisoners.

The vessel is controlled by Redhammer, the engineer responsible for transporting prisoners to the Iron Throne. It is the only practical route to the prison and, after the rescue sequence, the party cannot simply use it again to revisit either destination.

Location boundaries and hierarchy

The Submersible should be treated as a distinct small location, not as the whole of Flymm Cargo or the Iron Throne.

The warehouse, its basement, the dock hall, the vessel itself and the Iron Throne are separate spaces. The basement contains prison-like rooms, storage, documents and routes into the sewer system, but those areas are not part of the Submersible proper. Similarly, the Iron Throne is a separate underwater prison reached by boarding the vessel.

Named entries within the Submersible

The vessel has very little permanent population or independent content. The following names are directly associated with the Submersible itself:

The last two are not permanent residents. They are prisoners or mission characters who may return to the vessel during the rescue sequence. Redhammer is the vessel’s operator and the only named character normally found there before departure.

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Its immediate route is

  1. 01
    Lower City
  2. 02
    Flymm Cargo
  3. 03
    Flymm Cargo basement
  4. 04
    Submersible dock
  5. 05
    Submersible
  6. 06
    Iron Throne

Overview

The Submersible is moored in a hidden dock beneath Flymm Cargo on the Grey Harbour side of the Lower City. The dock is part of an industrial facility connected with the Steel Watch and the Iron Throne. Its concealment is important to Gortash’s operation: prisoners, supplies and construction materials can be moved beneath the harbour without using ordinary roads or city checkpoints.

The ship’s main gameplay purpose is to turn the Iron Throne into a reachable location. Before the party boards it, the Submersible functions as a staging point where the player can speak with Redhammer and make preparations. After docking at the prison, the party begins in a safe arrival area. The Iron Throne’s emergency countdown does not begin until a character descends through the hatch into the prison itself.

Once the party has entered the prison, the Submersible becomes the evacuation point. Prisoners must reach it before the countdown expires. If the party rescues Gondians, Duke Ravengard or Omeluum, they may appear aboard the vessel before the party leaves.

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Access and routes

Main route through Flymm Cargo

The normal route begins at Flymm Cargo, a warehouse on the eastern side of Grey Harbour. The building is watched by a Flaming Fist patrol, and its western entrance is locked. The warehouse also contains a concealed hatch leading to the basement.

The warehouse entrance can be lockpicked, while the basement hatch is partly concealed by crates and may require Perception to notice. The basement can also be reached from the Lower City Sewers through the route labelled Greasy, Smelly Way Up or Greasy, Smelly Way Down, depending on the direction of travel and the map’s wording.

Sewer route

The Lower City Sewers provide an alternative way into the Flymm Cargo basement. This can be useful if the warehouse is heavily watched or if the party has already found the sewer passage. The sewer connection does not make the Submersible a separate public fast-travel destination. It simply bypasses part of the warehouse.

Quest-led discovery

The Submersible may be revealed through several Act Three storylines, including Save the Gondians, Avenge the Drowned and Rescue the Grand Duke. The party does not need to encounter every one of these quests to use the vessel, but the surrounding quests provide different reasons to investigate Flymm Cargo and the Iron Throne.

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Main route through Flymm Cargo: From the basement

  1. 01
    Enter Flymm Cargo and locate the concealed hatch in the north-western part of the warehouse.
  2. 02
    Descend into the basement.
  3. 03
    Pass through the basement’s storage and prison-like areas.
  4. 04
    Continue through the passage behind the double doors.
  5. 05
    Enter the dock hall containing the moored Submersible.
  6. 06
    Speak with Redhammer and choose to travel to the Iron Throne.

Redhammer

Redhammer is the engineer in charge of the Submersible and the party’s immediate point of contact. He is found in the basement area beyond the storage rooms, close to the dock and vessel.

Conversation with Redhammer can reveal that the Submersible is used to transport prisoners to the Iron Throne. Depending on the party’s knowledge and dialogue choices, he can agree to take the party there. The exact dialogue route may vary depending on whether the party knows about the Iron Throne, has advanced relevant quests or has entered the area through another investigation.

Redhammer is also connected to Avenge the Drowned, because the Water Queen’s followers are investigating deaths associated with the underwater operation. His fate can change depending on the party’s choices in that quest. If the party gives him up, his corpse can later be found in the Water Queen’s Cellar.

Redhammer’s role

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The voyage to the Iron Throne

Boarding the Submersible is a major progression decision. The vessel immediately travels to the Iron Throne, and the party cannot use ordinary travel options to interrupt the trip. While the prison mission is active, fast travel and returning to camp are unavailable.

Before boarding, prepare as though the next area is a timed rescue mission.

These preparations are particularly important because the countdown begins once the party enters the Iron Throne. The Submersible is safe, but the prison is not.

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The Submersible as a safe area

When the vessel docks at the Iron Throne, the party initially arrives in a safe section of the Submersible. The rescue timer does not start until a character descends through the hatch into the prison.

This creates a useful preparation window. The party can remain on board, organise positions and make final decisions before entering the timed area. The vessel also serves as the extraction point: prisoners who reach it are safe from the prison’s countdown, although the party must still complete the evacuation and return there before the timer ends.

Practical use of the safe zone

The Submersible is not a rest area in the normal sense. It is a protected staging point within a sequence that must eventually be resolved.

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Practical use of the safe zone: A reliable approach is to

  1. 01
    Arrive at the Iron Throne.
  2. 02
    Keep the party together until the player understands the prison layout.
  3. 03
    Decide which characters will cover each corridor.
  4. 04
    Send mobile characters towards distant prisoners.
  5. 05
    Use summons or temporary allies to help open doors and block enemies.
  6. 06
    Leave at least one character able to return quickly to the Submersible.
  7. 07
    Descend only when ready to begin the rescue.

Rescued characters and post-mission changes

After the Iron Throne sequence, rescued Gondians gather along the edges of the Submersible. This gives the party an opportunity to speak with survivors before returning to the Flymm Cargo basement. The exact people present depend on who survived the prison rescue.

Possible mission-associated characters

Omeluum is especially useful during the prison escape because it can teleport itself and one ally back to the Submersible once per round. This is an ability of Omeluum during the Iron Throne mission, not a general transport feature of the vessel.

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Possible mission-associated characters

CharacterHow they relate to the Submersible
RedhammerPilot and engineer found before departure
Gondian survivorsGather aboard after being rescued
Duke RavengardMay be brought back from the Iron Throne
OmeluumMay be rescued from the prison and return to the vessel

Associated quests

The Submersible is connected to several overlapping Act Three questlines:

These quests do not all require the same objectives. For example, Save the Gondians focuses on the Gondian prisoners and the wider Steel Watch storyline, while Rescue the Grand Duke and The Blade of Frontiers involve Duke Ravengard and Wyll’s personal storyline. Retrieve Omeluum concerns the Society of Brilliance member held in the prison.

Progression warning

The Iron Throne is closely tied to the Steel Watch storyline. If the Steel Watch Foundry is destroyed before the party visits the prison, the Iron Throne may become unreachable. Treat the prison rescue as a priority before committing to actions that destroy the foundry.

The game also uses the Submersible as a point of no easy return. Once the party leaves the vessel after the mission, it cannot return to either the Submersible or the Iron Throne. Complete looting, conversations and rescue objectives before departing.

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Associated quests

Documents and lore connected with the vessel

Several documents found around Flymm Cargo, the Steel Watch operation and the Iron Throne explain the Submersible’s purpose. The Submersible Memorandum, for example, orders supplies to be delivered to the Iron Throne by way of the vessel and identifies Redhammer as the person who will facilitate the transport.

The Submersible is part of a larger logistical network rather than an isolated invention. Materials for the underwater facility were manufactured at the Steel Watch Foundry and transported by the vessel. The Iron Throne’s construction was overseen by Gortash’s agents, with sahuagin labour involved in the underwater work.

The following named documents are associated with the Submersible route or its surrounding facilities:

Most of these are found in Flymm Cargo, the Steel Watch Foundry or nearby facilities rather than inside the vessel itself. They should therefore be treated as route-associated literature, not as items guaranteed to be aboard the Submersible.

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Loot and facilities

The Submersible itself is not a conventional loot location. Its main rewards are access, rescued characters and quest progression.

These items belong to the Flymm Cargo basement and approach route, not necessarily to the interior of the Submersible. There is no evidence that the vessel functions as a shop, crafting station, permanent camp, fast-travel point or reusable transport service.

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Suggested exploration route

For a first visit, the following order minimises the chance of missing the surrounding content:

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Suggested exploration route: steps

  1. 01
    Explore the exterior of Flymm Cargo and note the Flaming Fist patrol.
  2. 02
    Enter the warehouse or approach through the Lower City Sewers.
  3. 03
    Search the concealed hatch and inspect the Flymm Cargo basement.
  4. 04
    Read or collect the nearby documents before boarding.
  5. 05
    Loot the passage and storage areas, including the Infernal Iron.
  6. 06
    Speak with Redhammer and exhaust relevant dialogue.
  7. 07
    Save the game.
  8. 08
    Confirm that the party is prepared for a timed rescue.
  9. 09
    Board the Submersible.
  10. 10
    Use the safe arrival area to organise the party.
  11. 11
    Enter the Iron Throne only when ready.
  12. 12
    Rescue as many prisoners as possible and return to the vessel.
  13. 13
    Speak with survivors aboard before leaving.
  14. 14
    Complete any remaining Flymm Cargo or quest-related actions before departing the area.

Common mistakes

Entering too early

Boarding the Submersible commits the party to the Iron Throne sequence. Do not board while intending to shop, change companions or rest.

Destroying the foundry first

Destroying the Steel Watch Foundry before visiting the Iron Throne can cut off access to the prison. Visit the prison first if you want to preserve the rescue opportunity.

Assuming the timer starts aboard the vessel

The timer begins when the party enters the Iron Throne, not during the initial arrival aboard the Submersible. Use the safe docked section to prepare.

Leaving without checking survivors

Rescued Gondians gather on the Submersible. Speak with them before leaving if you want their immediate dialogue and post-rescue information.

Treating the Submersible as reusable transport

After the party disembarks following the mission, access to the vessel and Iron Throne is closed. Finish the mission, looting and conversations before departure.

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Sources