You need three purple tablets to unlock the Neptune rocket in Subnautica's endgame

Purple tablets (also called Ion Power Cells) are the rarest crafting material in Subnautica, and the game requires exactly three of them to build the Neptune rocket — the vehicle you need to reach the final ending. You cannot progress past the mid-game without collecting all three, and there is no way to craft them or find substitutes.

Each purple tablet comes from a different source, and each one requires you to explore a specific biome and solve a puzzle or defeat an obstacle. The game is designed so you find them one at a time as you unlock new areas, which means you cannot farm them or gather extras.

Key Takeaways

  • The Neptune rocket requires exactly three purple tablets, and you must have all three before you can launch it.
  • One purple tablet is held by the Sea Emperor Leviathan in the Primary Containment Facility, and you must defeat or pacify it to take the tablet.
  • One purple tablet sits inside a locked container in the Lava Castle, accessible only after you have the blue tablet and the orange tablet.
  • One purple tablet is in the Quarantine Enforcement Platform, guarded by a Ghost Leviathan and locked behind a door that requires a purple tablet to open — you must find another way in or come back later.
  • You collect these tablets in sequence as you progress, so the order matters and backtracking is often necessary.

The first purple tablet: Sea Emperor Leviathan in the Primary Containment Facility

The first purple tablet drops from the Sea Emperor Leviathan when you encounter it in the Primary Containment Facility. This is the largest biome in the game, located deep below the island and accessible only after you have the blue tablet and the orange tablet. The Sea Emperor is not hostile — it will not attack you — but the facility itself is flooded with lava and Ghost Leviathans, so reaching it safely requires a strong vehicle and good preparation.

When you reach the Sea Emperor, it will give you the tablet as part of the story sequence. You do not have to fight it or do anything special; the game progresses automatically once you are in the same chamber. After you take the tablet, you can leave the facility and return to the surface.

The second purple tablet: Lava Castle in the Lava Zone

The second purple tablet is locked inside a container in the Lava Castle, a structure in the Lava Zone on the far side of the map. The castle itself is not hard to find — it is a large building made of coral and metal — but the container holding the tablet is locked with a keypad that requires a code. The code is 1454, and you can find it written on a PDA or databank entry elsewhere in the game.

To reach the Lava Castle safely, you need a vehicle that can handle extreme heat, such as the Prawn Suit with a Thermal Reactor module or the Neptune submarine. The path down is long and you will encounter Lava Lizards and other hostile creatures, so bring weapons or be prepared to run. Once you open the container, take the tablet and leave.

The third purple tablet: Quarantine Enforcement Platform

The third purple tablet is in the Quarantine Enforcement Platform, a massive facility on the far edge of the map in the Lava Zone. This location is the most dangerous because it is guarded by a Ghost Leviathan and surrounded by lava. The tablet sits in a locked room that requires a purple tablet to open the door — which creates a puzzle, because you need a purple tablet to get the purple tablet.

The solution is to come back to this facility after you have collected the other two purple tablets. Use one of them to unlock the door, take the third tablet from inside, and then you have all three. Alternatively, some players find a way to bypass the door using the Prawn Suit's grappling arm or by exploiting the terrain, but the intended route is to return later with a tablet in your inventory.

The order matters: why you cannot grab all three at once

The three purple tablets are locked behind different progression gates. You cannot reach the Primary Containment Facility without the blue and orange tablets, so you cannot get the first purple tablet until mid-game. The Lava Castle is accessible earlier but still requires heat-resistant equipment. The Quarantine Enforcement Platform is the last location you visit, and its locked door forces you to come back after collecting the other two.

This design means you will naturally collect the tablets in a specific sequence as you explore. If you try to rush to one location early, you will hit a locked door or a biome you cannot survive in yet. The game guides you through the correct order by making earlier locations inaccessible.

What happens after you collect all three purple tablets

Once you have all three purple tablets in your inventory, you can build the Neptune rocket. The rocket is constructed in a special facility on the island, and building it requires the three tablets plus a large amount of other materials — titanium, gold, copper, and various electronic components. The rocket takes time to build, and you watch the construction progress through cutscenes.

After the rocket is complete, you can launch it and reach the final ending of the game. This is the only way to finish Subnautica's main story, so collecting all three purple tablets is mandatory if you want to see the ending.

Frequently Asked Questions

Can I craft purple tablets or find more than three?

No. Purple tablets cannot be crafted at any workbench or fabricator, and there are only three in the entire game. You cannot farm them or find extras. If you lose one or drop it in lava, you will have to reload a save or restart the game.

What if I use a purple tablet on the wrong door?

The only door that requires a purple tablet is the one in the Quarantine Enforcement Platform. If you use a tablet there before collecting the other two, you will lock yourself out of that room until you get another tablet. Plan ahead and collect the other two tablets first, then use one to unlock the final room.

Do I need purple tablets for anything other than the Neptune rocket?

The only use for purple tablets in the base game is building the Neptune rocket and unlocking the door in the Quarantine Enforcement Platform. They have no other purpose, so do not waste them on anything else.

Can I get the purple tablets in a different order?

You can collect the Lava Castle tablet before the Sea Emperor tablet if you have the right equipment, but you will always need to save one tablet for the Quarantine Enforcement Platform door. The game's progression gates make it difficult to deviate from the intended order, but speedrunners sometimes find alternate routes.