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The TFTD Research Tree Bug Avoidance Guide

A needlessly wordy article by NKF


The designers of X-Com Terror From The Deep seem to have attempted to make the research process in TFTD much more complicated than its very straightforward predecessor's research tree. They have succeeded in doing this, but have also introduced many glaringly unacceptable errors in the process that can prevent you from completing the game.

Some players may have had the luck of not bumping into any of these errors by picking all the right research at the right time, or have a game that doesn't seem to have these problems. Unfortunately, as the research order in TFTD is non-linear, that is to say you can research anything you've got in any order you want, a lot of us are less fortunate. This guide should help to assist and point out some of the stickier bits.

Also note that this is not a reproduction of the research tree. There are many documents in a variety of formats describing the complete research tree on the Internet that you can peruse. This document is merely a supplement.


The word 'prerequisite' is used quite frequently throughout this document. As prerequisite is not an everyday word, here is its definition.

Pre- means 'before', Requisite means something that is required in order to achieve something. In Layman terms and in context with the game: to get this thingy, you need to research or have these other thingies first.

Spoiler Warning

While this may spoil the game if you are new to it, it is better to be informed than to make a mistake that is irreversible. The game IS hard, even for X-Com UFO veterans.

With the exception of MC technology, this document discusses a branch of the research tree that will take you from the very start of the game all the way to the final chamber in T'Leth. (Well, not exactly, but it'll give you everything you need!)

Glitches in the System

There are two major occasions where research can grind to a halt:

  • An alien is required to further research AFTER certain projects are completed
  • An object is needed in storage before research is completed


A large portion of the research can be cut off by researching an alien in the incorrect sequence.

For example, in order to open a new research branch, you need to have researched project A and B and then interrogate alien C in order to get new technology D. If you were to interrogate alien C before completing research on A and B, technology D will not appear for research once you've completed research on A and B. In order to get D to appear, you must capture another alien and interrogate it again.

So, as a rule of thumb, if an alien is a prerequisite for any particular tech item, it is highly recommended that you hold off the completion of the interrogation until all the prerequisites have been researched.

The Deep One Dilemma

The primary research path at an abstract level looks roughly like so:

Armour Subs T'Leth

The path for Armour looks roughly like:

Deep One Corpse Aqua Plastics Plastic Aqua Armour Ion Beam Accelerators Live Deep One Terrorist Ion Armour Magnetic Navigation Mag. Ion Armour

Not all of the technologies need to be reseached in the exact order - with the exception of the live Deep One, which should only be reseached after you have met the other prerequisites for Ion Armour.

Without Armours you won't get to research advanced subs; without advanced subs you can't reach T'leth and defeat the aliens once and for all.

You will need a living specimen and a corpse. In older versions of the game, where you need a lobsterman navigator to get magnetic navigation, getting a live Deep One Terrorist is not that important. However, in TFTD versions with the v2 update, success hinges on getting a living Deep One terrorist.

Deep One Terrorists can be found in most Gill-man land missions. They do not appear underwater (1), and are replaced with Xarquids if you shoot down Gill-Men terror ships.

(1) you may find some Deep One Terrorists in the second level of T'Leth; however, you may only get there after when you already have the tech they provide.

Don't worry if you missed them, Gill-Man terror sites do still appear when it's late in the game, although they are abundant early in game.

Deep One Terrorists also appear in 'mixed' alien crew land missions. A mixed crew is made up of a variety of species, and in terror sites and base attacks, will be supported by a variety of land-based terror units, which includes the Deep One Terrorist as well as the odd Xarquid (which normally replaces the Deep One Terrorist for underwater missions).

Just promote a terror site by leaving any ships on terror missions alone, or encourage the Gill-Men or 'mixed' crews to attack your base by shooting some of their USOs down near your base. You might also want to dismantle your M.C generator to improve the likelihood of an attack.

Before starting research on the Deep One Terrorist, refer to the Ion Armour section.

Finally, researching an alien medic and getting information on the Deep One Terrorist or its corpse is not the same as researching the real thing. You will not get any research benefits from the alien medic's report. Keep this in mind.

The Tasoth Commander Trap

Note that it is unfortunately difficult to double check the validity of this bug at the present time, so this section has been intentionally left vague for now, but is left for the benefit of the that may experience it.

Most copies of the game do not recognise the Tasoth Commander as a legal alien (Although the alien/rank combination can still exist) and cannot be researched. If for whatever reason one does somehow appear on your research list, do not complete the research on it until after obtaining a Leviathan and the final mission launch button. Researching it will prevent these topics from being researched through normal means.

If you're unsure whether you'll face this bug or otherwise, update your game with the v2 patch if you are using the Dos version. The Collectors edition of TFTD is already updated to v2.

Required Objects

The MC Reader and Sub Construction samples

These two items, the MC Reader and the Sub Construction store item, are special in that they will only become available for research if and only if a sample is available in your general stores before completing research for their prerequisite technologies.

If you do not have any when completing research on the last of their required technologies, they will NOT appear later even after acquiring a few samples.

For example: If you've done Zrbite and are about to finish research on the Transmission Resolver, make sure that you have the 'sub construction' item in stores before the research on the Transmission Resolver hits 100%, or vice-versa.

Between the MC Reader and the Sub Construction store item, the 'sub construction' store item is required to win the game. The MC Reader is optional.

Note: This does not apply to Aqua Plastics. You can research it even without any samples.

Note: If this happens to you and you don't have a suitable save game to revert, you can still rescue your game using a hex editor. Open the file RESEARCH.DAT that resides in the appropriate save game folder and set the byte at the hexadecimal offset 0x1B4 to 1. This will allow you to research Alien Sub Construction. (It will allow you to research it even if you don't have the prerequisite technologies, in fact, but you wouldn't cheat that way, would you?)

Note: Another way to combat the research tree bug for Alien Sub Construction is to modify PROJECT.DAT. Open the file with a hex editor and set the byte at the hexadecimal offset 0x26 to 01. This will make Alien Sub Construction appear in your research, then all you have to do is assign some scientists and complete it. Note that this bypasses all prerequisites. (tested on TFTD v2 but should also work on other versions)

Modify save games at your own risk. You should always create a backup first.

Version differences

There are two versions of TFTD. The original unpatched version of TFTD and the one with the v2 update.

Players with the Collectors Edition of TFTD have the version with the v2 patch.

The known changes in the research tree are as follows:


A Lobsterman Navigator is needed to research Magnetic Navigation

Ion Armour is not required for Magnetic Ion Armour. All the technologies you need for Magnetic Ion Armour are Plastic Aqua Armour, Ion Beam Accelerators and Magnetic Navigation.


Magnetic Navigation can be researched as soon as one is in storage. The lobsterman navigator is NOT required.

Ion Armour is required for Magnetic Ion Armour. Magnetic Ion Armour now just requires Magnetic Navigation and Ion Armour.

Yes, in other words, the v2 patch makes it easier to get Mag. Ion Armour. However, it also means that winning the game hinges on your ability to obtain a live Deep One terrorist AND researching it in the right order.

If you patch your game and reload a campaign created before the patch, you might face a few research problems. It's not that common, but you might find that you'll have some trouble with researching the more advanced armour via the V2 method. There should be no problems if you haven't even started on the Ion Armour or Mag Ion Armour yet. It's mostly for campaigns where you're already half-way through researching the armour.


Only difference from v2 (per StrategyCore) is that the MC Reader bug is fixed: it can be researched even if you didn't have a sample when MC Lab was complete. Note that TFTD CE is v2 and does not include this fix.

The Good Bit

The all important good bit gets down to the brass tacks. It's probably why you're here, so dig in!

Alien Sub Components

Technology Prerequisities Notes
Zrbite None A clump of Zrbite can be found underneath an Ion Beam Accelerator unit. If any explosive detonations occur near the IBA unit, it will be destroyed as it is very brittle (or rather, the IBA will blow up).

You can pick up these clumps, but finding a clump only occurs in unusual circumstances. For example, throwing an unconscious soldier into an IBA and waiting for him or her to wake up. Falling down onto one or walking into one with the walk-through-walls bug.

Xcomutil users will often find Zrbite clumps lying about when selecting a USO floor map that is not the same as the type of USO you're actually attacking.

Aqua Plastics Deep One corpse You don't need any aqua plastics to research it. You just need the Deep One corpse.
Ion Beam Accelerators None Ion Beam Accelerator units are found in intact alien USOs. Most smaller enemy subs will lose their IBA units if shot down, although some of the IBA units may survive if they're in larger ships.
Magnetic Navigation None (TFTD v2) or Lobsterman Navigator (TFTD pre-v2) In older versions of the game, a Lobsterman Navigator is required to get Magnetic Navigation. Otherwise, it should appear immediately on the research list once one is in storage.
Transmission Resolver Magnetic Navigation  
Sub Construction Sub Construction (item), Zrbite, Transmission Resolver Keep at least one 'sub construction' component in storage before completing either of the two prerequisites. If you don't have one when both the prerequisites have been met, you will not get the 'sub construction' tech item, which is required for the advanced submarines


Technology Prerequisities Notes
Plastic Aqua Armor Aqua Plastics Aqua Plastics are obtained from a Deep One corpse. You need not have any actual aqua-plastics in storage to get the Aqua Plastics research item.
Ion Armour Ion Beam Accelerators, Plastic Aqua Armour and a Deep One Terrorist Research the first two prerequisites in any order you wish. However, you MUST research the live Deep One Terrorist LAST. If you researched this alien earlier, you won't get Ion Armour. Capturing another Deep One Terrorist is possible, but there is a small chance that you will not be able to research any more of them.

This is especially important in versions of TFTD patched with the v2 update, as without Ion Armour, you cannot get Magnetic Ion Armour, which in turn is needed to get the advanced submarines.

Magnetic Ion Armour
(TFTD v2)
Ion Armour, Magnetic Navigation If you don't know what version of the game you have, the method in which you obtain Mag. Ion Armour will tell you which one it is.

For versions v2 and up, Magnetic Navigation becomes available the moment you have a sample in storage. Also keep in mind that Ion Armour is compulsory.

Magnetic Ion Armour
(TFTD pre-v2)
Magnetic Navigation, Ion Beam Accelerators In older versions of TFTD, to get Magnetic Navigation, you need a Lobsterman Navigator. Keep in mind, Ion Armour is not compulsory.


Technology Prerequisities Notes
Manta Magnetic Ion Armour, Sub Construction Refer to the sub component section for notes on Sub Construction. This submarine allows construction of the more advanced SWS.
Hammerhead Manta  
Leviathan Hammerhead, Lobsterman Commander The Lobsterman Commander should be researched after the Hammerhead. Also, for your convenience, don't forget to research 'alien origins' first so that you don't have to capture a third lobsterman commander to win the game.

If you did not research the commander and the hammerhead in the right order, don't worry, just research another Lobsterman Commander.

Note (to Hexedit): Open the file RESEARCH.DAT that resides in the appropriate save game folder and set the byte at the hexadecimal offset 0x27A to 1. This will allow you to research The Latest Flying Sub aka Leviathan

Techs to Win the Game

Technology Prerequisities Notes
Alien Origins Any live alien
The Ultimate Threat Alien Origins and a Lobsterman Commander Research the commander last. If you researched the commander before alien origins, don't worry. Just research another commander.

* A Lobsterman Navigator or Gillman Commander can also substitute for the commander.

T'Leth, the Alien's City The Ultimate Threat and a Lobsterman Commander (another one) You need to research another lobsterman commander.

It is claimed that researching a Tasoth Commander at any time will cause theTasoth Commander Trap and prevent this topic from becoming available. Note that evidence of this bug are so far purely anecdotal.

Disruptor Pulse Launcher (optional)

Optional as you do not need the DPL torpedoes to win the game. It's not a serious problem, but is mentioned anyway to ally any concerns about the launchers not appearing for research.

Technology Prerequisities Notes
Disruptor Pulse Launcher Zrbite As soon as you've researched Zrbite, you can start research on the DPL launcher and its ammo - assuming you had a sample in storage upon completion of the project.

However, unlike Sub Construction and the Mind Probe, the DPL Launcher has a failsafe. If you did not have any samples upon completion of Zrbite, you will be able to make them appear for research the moment the next research project is completed.

Molecular Control Technology (optional)

Optional because you don't need MC tech to win the game. But as its research branch has a notable bug, is included as well.

Technology Prerequisities Notes
M.C.-LAB Any Live Terrorist Either of the two terrorist units will give you the M.C.-Lab.

Deep One Terrorists generally follow Gill-men and Calcinites associate themselves with Aquatoids. Both aliens can be found in 'mixed' crew land missions.

MC Reader MC Reader (item), M.C.-Lab The MC Reader research item will only become available if research on the M.C.-Lab is completed while an MC Reader is in storage.

If you miss out on this, you will NOT get the MC Disruptor or the MC Generator for the rest of the campaign.

MC Disruptor MC Reader and
any live Tasoth
Excluding the Tasoth Commander, of course.

While the Ufopaedia says it only works underwater, this item will work on land. I believe the text was meant to say that only aquanauts with 'MC implants' can use it, the word 'underwater' seems like a typo that was never removed.

Again, if you research the live Tasoth before completing the research on M.C. Reader, you will be forced to capture and interrogate another live Tasoth in order to get the M.C. Disruptor technology.

MC Generator MC Disruptor This item will protect your base from being found, but it does not work 100% of the time. Aliens can still attack shielded bases if their scouts are lucky. The magnitude of USOs successfully spotting your base is reduced.

Melee Weapons (optional, but handy)

Vibro Blade research comes from the Calcinite corpse. Once that research is done, if you've autopsied a Gillman corpse by that point (more than likely) you also get to research Thermic Lance. Once Thermic Lance is researched, Heavy Thermic Lance, last in this line, can be researched

Obligatory Disclaimer Claptrap

This document will not always be 100% accurate, as the game tends to behave differently for different players with different computer systems and game editions.

These notes are derived through many controlled tests and observations with the MS-DOS edition of Terror From The Deep with the TFTDv2 patch. Any noticeable difference between the patched game and the older versions are noted. Otherwise, these notes are valid for practically any version of TFTD available on the PC, with the possible exception of TFTD for the Sony Playstation.

TFTD, Terror From The Deep, X-Com, XCOM, et. al. originally developed by some very fine people. Originally distributed by Microprose. Now? Who knows.

As the purpose of this document is to inform, feel free to distribute any information in this document as you see fit.

Many thanks for the input and feedback from the regular posters on the Xcommand and X-Com Tactical Command forums for assisting in the preparation of this document. Some indirect thanks to the fine folks on the Usenet newsgroup as well. Extra bits and pieces here and there picked up from the forums as well.