Video Game / X-COM: Terror from the Deep

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X-COM: Terror from the Deep is the '95 follow-up to X-COM: UFO Defense (or Enemy Unknown, depending on your nationality) which tries to change as little as possible. After their last failed bid to Take Over the World in the previous game, the aliens on Cydonia sent a message...to the oceans of Earth. Turns out they visited Earth a long time ago, and then never left due to crash-landing. Now, they're upset that humanity had the audacity to deny their space-borne brethren the rite of conquest, so they're picking up where the war left off. They're still UFOs. Just underwater.

TFTD has the look of a "reskin" or an expansion, but is an actual sequel to UFO Defense. It has the same game engine, but the difficulty and map size are increased, making it much lengthier. There are also UI improvements: You can reserve time to kneel as well as shoot, and it remains set for the rest of the battle (or until you un-toggle it), streamlining the tactical phase significantly. Most of these features were bundled into the open source clone of UFO (OpenXCom) in 2010.

UFO cares about you. It wants you to have a good time. There is a bit of cheating involved (reaction time preference), but overall, it treats you nicely if you follow the house rules. Terror from the Deep is another ball of wax. That reaction shot will always hit you, and you won't get a chance of surviving. Chrysalids can fly now. Gauss weapons (laser equivalents) have ammo requirements. Aliens holding one-handed Blaster Launchers. Certain weapons will function underwater but not on land. Multi-part Terror Missions. Only a Lobsterman Commander can get you the game-ending research, rather than an easier Aquatoid or Gillman. Terror from the Deep will put hair on your chest. It is a one-sided alien mosh pit of death and doom.

Firaxis considered remaking Terror from the Deep, but decided to release Enemy Within and XCOM 2 instead. However, the ending to XCOM 2 hinted that a remake of classic TFTD is still a possibility. Or you can just play the new XCOM with an aquarium in front of your monitor.

For tropes shared with the original X-COM, see X Com UFO Defense.

Tropes

  • Achilles' Heel
    • Tentaculats: Unlike the UFO Defense counterpart which can damage tanks, Tentaculats can't damage your SWS, and will still stupidly try to attack them anyway to no avail. So always bring one if you are expecting them.
    • Lobstermen: While even the alien's own Sonic Cannons can barely scratch them, they are surprisingly vulnerable to both melee attack and thermal weapons — if you haven't got the Vibro Blade line of research opened up yet, make sure you pack some Thermal Tazers and/or Thermal Shok Bombs.
    • Triscenes: They can take some Sonic Cannon punishment, but its non-existent underside armor means a single cheap magna-blast grenade thrown under it will most often kill it.
    • Deep Ones: They have a ranged attack, but no reaction fire ability. So it's perfectly safe to position your troops for an optimal shot or run up to them at whack them with melee weapons. They are totally harmless during your turn.
  • The Aesthetics of Technology: Aliens have a Used Future look.
  • Alien Popsicle: The aliens use cryogenic stasis chambers to remain dormant for thousands of years. You can also sell these chambers as Vendor Trash.
  • And I Must Scream: Molecular Control is functionally the same as Psionic Control from the first game. However, the name (and subsequent research) indicates that you are fully aware of what's happening and completely unable to control your body as the aliens make it do whatever they want to do. Aquanauts are recover from Molecular Control have a very high chance of panicking or going berserk.
    • Also, the Bio-Drones. Full stop.
  • Animal Motifs: The smaller USOs have a manta-like design.
  • Animated Armor: Calcinites are giant blobs of protoplasm which seek out antique diving suits strewn across the sea floor. Once they've filled the suit up, it springs backs to "life."
  • Apocalypse How — Continental: Failing to stop the aliens means their city-weapon rises from the deeps and kills pretty much everything. When you win, the aliens still have the last laugh, as the destruction of T'leth results in a near-Planetary apocalypse.
  • Armless Biped: Like the Reapers, the Triscenes don't have arms. Unlike the Reapers, they make up for it by carrying two Heavy Sonic Cannons on their bodies.
  • Armor-Piercing Attack : While there is an "Armour Piercing" damage type, they aren't good at penetrating armornote . This job instead applies to Vibro Blades, Thermic Lances, and Heavy Thermic Lances. While you can kill the absurdly heavily armored Lobstermen without themnote , once you realize that they take 200% damage from those weapons, you'll be carrying them with you everywhere.
  • Artificial Stupidity: Are any of the aliens in a given mission equipped with Sonic Pulsers? They'll also be carrying either a Vibro Blade, Thermic Lance, or Heavy Thermic Lance — and yet they never use them, even if they've run out of Sonic Pulsersnote .
  • Aquatic Mook: With the exception of the few surface-only Terror units, all Aliens are aquatic.
  • Ass Kicks You: Once again, note the curious distribution of defensive power on the Magnetic Ion Armor. The back plate is the second-strongest part of the suit, and the side plates are weakest. While counterintuitive to say the least, this means it is safer to turn your back to the aliens than to let them hit you from the side. Looking at the UFOpedia picture, it's due to that bulky thing hanging off the back.
  • Awesome, but Impractical: The Sonic Cannon is the most powerful non-explosive weapon in the game (the Disruptor Pulse Launcher does the most damage, period), but is only a few points stronger than the Sonic Blasta-Rifle. In addition to being very heavy, the Sonic Cannon also requires half an Aquanaut's time units to fire a snap shot, has worse base accuracy than the Blasta-Rifle, and only 2/3rds as much ammo per clip as the Blasta-Rifle. By comparison, the Blasta-Rifle does less damage, but is more accurate, easier to carry around, and can allow a unit to move and fire at a respectable pace. On top of all of that, the Blasta-Rifle's damage is enough to outright kill everything that the Sonic Cannon would kill, and anything that the Sonic Cannon wouldn't kill, the Blasta-Rifle wouldn't kill either. Suffice to say, Sonic Cannons should be sold for money, you should arm your troops with Blasta-Rifles, and laugh as the late-game enemies all find themselves crippled by all the drawbacks of Cannons once they are exclusively armed with them.
  • Bag of Spilling:
    • X-COM was disbanded after the First Alien War thanks to politics, reduced to the underwater Elerium salvage team financed by a tycoon, until the arrival of aliens prompted the re-constituted Funding Nations to reboot the program.
    • In addition, you will start out with basic weapons and no armor because all the research from the First Alien War is functionally useless underwater: alien alloys react poorly to seawater, meaning they can't be used for armor or weapons (invalidating plasma weaponry), and lasers are impractical underwater due to blooming and other issues (invalidating laser weaponry). Of course none of this explains why you can't simply use the old alien weapons for missions when you aren't underwater, such as terror alerts or base defense, but the game still doesn't let you.
  • Blob Monster: The Calcinites, although they were contained in a humanoid diving suit.
  • Boarding Party: The Cruise Ship and Transport Ship Terror Missions.
  • Boring, but Practical: Sonic Blasta Rifles. They are basic single-shot rifles. While not the most powerful or stylish weapons in the game, they are extremely well balanced as a light weight, high damage weapon.
  • Brain in a Jar: The Bio-Drones.
  • Broke Your Arm Punching Out Cthulhu: The end of Terror from the Deep results in T'leth's destruction spreading chemicals all over the world's oceans and thus snapping a few links off the food chain. Oops.
  • The Captain: The highest rank the X-COM soldier can achieve. You can have one Captain for every 30 Aquanauts you employ (and if you're employing enough at the same time to have two Captains, you are massively overstaffed).
  • Cloning Blues: Just about all of the aliens are cloned, much like the first game. They don't have the personal autonomy to worry about it, though.
  • Commanding Coolness: The second-highest rank the X-COM soldiers can achieve: you can have one Commander for every 21 Aquanauts.
  • Derelict Graveyard: Some tactical maps feature sunken ships or crashed airliners.
  • Diabolus ex Nihilo: The Great Dreamer. Apparently you can't kill it. Nothing can. What works, however, disrupting it's awakening so that it can't wake up and destroy everything: whether this actually kills the Dreamer is unknown. Nobody on Earth can guess where the creature came from as it's a closely-guarded secret: none of the aliens actually know.
  • Diesel Punk: The aliens show elements of this.
  • Divided States of America: People's Republic of Alaska.
  • Downer Ending: As highlighted on Pyrrhic Victory, even if the player wins things all go downhill for Earth, culminating in the Crapsack World of Apocalypse.
  • Drone of Dread: The "Geoscape" theme.
  • Early Game Hell: At the start of the game, money is tight, your single base provides very limited coverage for the world, your technology is massively outclassed by the aliens, your troops lack combat skill, and the lack of armor means a hit from practically anything will kill them. Furthermore, new players may not know what research to prioritize to best bring their forces up to par with the aliens.
  • Eenie, Meenie, Miny Moai: They may show up on island Terror Missions. Must be some kind of fad in 2040.
  • Eldritch Abomination: The Big Bad is the Great Dreamer in T'Leth, and He Waits. You need to go there and make sure He keeps dreaming, since if He wakes up, He'll be unstoppable.
  • Everything's Harder with Heavily Armored Cyborg Dinosaurs with Mounted Sonic Cannons.
  • Fish People: The Gillmen, being early humans who were genetically modified to survive underwater, and the Lobstermen, being actual lobsters that were genetically modified into bipedal soldiers, both fit. Autopsies reveal that other creatures, like the Deep One and the Hallucinoid, also have some human and aquatic DNA, but they're so far removed from humanity they don't count for this trope.
  • Flying Saucer: Several examples.
    • What do you get when you take the cyberdisc, miniaturize it, waterproof it, replace the CPU with a still-conscious human brain and replace the plasma cannons with a concentrated sound wave generated by said brain's reactions to the inherent agony of the process? The answer is: Bio-Drones. Oh, and they explode when they die.
    • There's also the Dreadnought, TFTD's answer to UFO's Battleship, which almost looks exactly like its UFO counterpart, in that it looks like a giant Flying Saucer.
  • The Future: TFTD is set far enough the 21st century — that is, far enough to prevent overlap with the previous campaign (regardless of how bad you suck at X-Com, it probably didn't take forty years to complete). The initial alien invasions caused turmoil among the funding nations, splitting some into blocs while annexing others into greater superpowers. Alaska is now a people's republic, China and India formed an Asian Coalition, everything west of the Mississippi has been retaken by Mexico, Europe finally got its act together, and Africa/Egypt are currently governed by private enterprises.
  • Game-Breaking Bug
    • Never research the Tasoth Commander. (Fixed in the CD version.)
    • TFTD has the Research Tree bug, where researching something too early can accidentally block off advancement in that research path. Most crippling is the Live Deep One bug. If you research a Live Deep One before you research the prerequisites for the Ion Armor, you won't be able to research the ships needed to complete the game. Thankfully, most of these have been patched away by the Windows 95 version.
    • If an explosive object is detonated by a stray shot from a Deep One (which is actually extremely unlikely, as the Deep Ones have good accuracy and their electric acid shots have a very, very low probability of causing an explosion, usually just melting the object instead), the aliens will freeze up, and their turn never ends.
  • Gameplay and Story Segregation:
    • Molecular Control supposedly works through mind control implants. However, Molecular Control attacks don't require the victim to have a mind control implant: it's implied that this is why MC attacks must be repeated every round (without the implant, there's no lasting control of the victim), but that just raises further questions, such as why your MC-enhanced Aquanauts are not constantly under alien control after getting their own implants.
    • The Interceptor Barracuda not only boasts propulsion that allows supersonic speeds underwater, it's also capable of flight and VTOL. Truly an engineering marvel. (Alien ships also travel ridiculously fast considering they're miles underwater, but then, alien technology...)
    • Zig-zagged with port attacks:
      1. Your troops, being idiots, are still wearing their weighted shoes and diving suits, losing any dexterity one would expect from fighting on the surface instead of 10,000 ft. below sea level.
      2. Machine guns and heavy artillery aren't available either, for obvious reasons, which is fine because the aliens are restricted to aquatic weapons also. But the Hydrojet Cannon and the Torpedo Launcher, which both use propeller tech to drive their projectiles, are completely ineffective on land.
  • Genre Shift: According to Julian Gollup, after X-Com he was burned out and flat out of juice. He was done with games about aliens, but he expressed interest in developing one based on the Cthulu mythos. Some of these ideas were incorporated into TFTD and Apocolypse.
  • Giant Enemy Lobsters: The much feared Lobstermen. Until you acquire flying suits and mind control. As they are invulnerable to basic pistols, they become the best target practices. Or, when you get Vibro Blades.
  • Glass Cannon
    • The Tasoths are a varient of this. All Tasoths have potent M.C. strength, but on lower difficulties, aquanauts with high enough M.C. stats can use mind control on them with relative ease. In addition, lower-ranking Tasoths have no M.C. abilities, meaning they can't use M.C. attacks, and their stats make them subpar combatants (comparable to a Gill Man or an Aquatoid). They tend to go down very quickly, especially since they are introduced after the deadly Lobstermen.
    • Deep Ones possess an electric acid attack that can kill an aquanaut in one hit, regardless of armornote , but are fairly easy to kill, even with basic weaponry. They do, however, get a lot of attacks.
  • Guide Dang It!: A Deep One corpse is also required to get aqua plastic armor, which isn't hard to get, but may not be an obvious leap if you are new to the game and leaves your men naked for longer.
  • Harpoon Gun: Your starting "standard rifle". Five darts at point-blank range won't even faze a Gillman, at least on higher difficulty levels. If you bring a harpoon gun into battle, you can almost hear the aliens laugh. The pistol version, the Dart Gun, is even weaker, and practically useless except for Stat Grinding (more hits to kill an alien = more experience gained).
  • Heavily Armored Mook: Lobstermen are so well armored they can absorb an obscene amount of damage. If you run into these guys before you've researched anything beyond the starting weapons, you should leave immediately. Darts and Harpoons are about as effective against them as tennis balls.
  • Hot Sub-on-Sub Action: Your subs versus USOs.
  • Humanoid Abomination: The Deep Ones. They're something like an underwater Frankenstein's monster.
  • An Ice Person: Hallucinoids are prehistoric jellyfish that were modified to use a powerful chemical freezer. They attack by using a melee attack that literally freezes targets to death. They are supposed to have a similar ranged attack, but almost never use it due to a bug.
  • If It Swims, It Flies: USOs (Unidentified Submersible Objects) and your flying subs that intercept them. Both can fly over land, with a handwave stating that the engines are convertible to work in the air without issues, but weapons can only be fired underwater due to their design (a torpedo is not the same thing as a missile, for example).
  • Implacable Man
    • The Lobstermen. They. Will. Not. DIE. Let's put it this way... unless you drop them with the heaviest melee weapons, chances are, they're actually unconscious, not deadnote .
    • The Triscenes are Implacable Dinosaurs, until you find their weakness (their non-existent under armour).
  • Ironic Name: Gillman Terror units are named "The Deep One", yet you never find them in the ocean.
  • Kill It with Ice: Subverted. Freezing weapons, including Thermal Tasers and Thermal-Shok Bombs, are the equivalent of Stun Weapons from Enemy Unknown. Instead of killing targets, they harmlessly freeze them, allowing you to capture aliens.
  • Lethal Lava Land: Sort of, one of the TFTD combat mission terrains consists of underwater mini-volcanoes leaking cooled lava. They have no effect on your soldiers and enemies, but they do provide illumination in night missions.
  • Lizard Folk: The Psychic Tasoth.
  • Lost Colony: T'Leth is a massive colonizing ship that crashed 65 million years ago.
  • Lovecraft Lite: The alien horde has cousins dwelling under the sea. Their final goal is to awaken the "Ultimate Alien", a giant squid which is entombed in the ancient sunken city of T'leth. And things go as dark and pessimistic as Lovecraft would have written it (only without the scope of a Cosmic Horror Story).
  • Make Me Wanna Shout
    • The Aliens' Sonic Weapons, TFTD's equivalent of UFO's Plasma Weapons.
    • Bonus points for the Bio-Drone, whose sonic beam is based on the original vocal cords of the brain that pilots it, meaning that it literally screams its enemies to death.
  • Master of None: The Gillmen, though they become Jack-of-All-Stats at higher difficulties.
  • Meet the New Boss: Although "not alive but somehow not dead" the Ultimate Alien is subliminally commanding the submarine fleet. It fills the old role left over by the brain.
  • Military Mashup Machine: The alien subs, as well as XCOM subs, are all capable of flying over land. According to the lore, the turbines that drive both spin up and turn into actual jet engines above water, meaning that the subs are actually air/aquatic hybrids. The mounted weapons only work underwater though, which means a sub will pursue a USO until it goes back in the water before attacking.
  • Mooks: The poor Gillmen. They have horrible aiming skills, they panic easily, and are even more fragile than the Aquatoids. It is heavily implied they they are enslaved by the other aliens and are considered totally disposable.
  • Multi-Armed and Dangerous: The Lobstermen, mostly cosmetical in regards of equipment, but not for their close combat ability.
  • Nerf:
    • Dye grenades produce an octopus-like ink spray. Theoretically identical to Smoke Grenades (from UFO Defense), the dye's area of effect is much lower. Instead of providing a compact but effective 6x6 grid of cloud cover, the Dye Grenade creates a tiny puff of dye which spreads across the battlescape over the course of several turns.

      Because cloud cover provides the greatest protection within the first few turns after being released, this pretty much defeats the purpose. A much quicker solution is to simply detonate an explosive for an instantaneous cloud of foam. (It is very likely that the team responsible for TFTD may have mistyped the dye grenade's strength as 10 instead of 100. Some fan patches increase the Grenade's strength)
    • Gas-propelled weapons (Terror's substitute for rockets, grenade launchers and miniguns) do not work on the planet surface. Thus leaving you with the Gas Cannon as your most powerful weapon available and severely limiting your offensive capabilities until you have Gauss technology, which will not be available until after your first Terror Site at best. (You can get Gauss pistols by the first Terror Site, but they have low accuracy and attack power.)
    • In UFO, Flight Suits would leave Terror Units, such as the fearsome Chryssalid, at your mercy. In TFTD, the Magnetic Ion Armor doesn't work during Port Attacks, so you're better off giving everyone plain Ion Armor.
    • Gauss weapons. The Gauss Pistol is researchable as soon as the game begins, much like the Laser Pistol (UFO), but is less accurate due to the high rate of fire. (Contrary to the official Ufopaedia entry, the Gauss Pistol is not accurate.) Also, unlike the laser pistol, this thing chews through ammo at an alarming pace. Because of these limitations, it can be treated as the 'uzi' of the Gauss family.

      The other, more bitter irony of Gauss technology is that most of the aliens encountered are highly resistant to it.
    • The Sonic Cannon, when compared to the Heavy Plasma in UFO. While slightly more powerful, it lacks automatic fire capability, fires slowly, and has a small magazine size. This is actually good from a game balance standpoint, since each of the Sonic weapons now has a distinct role. In effect, the Sonic Cannon works like a sniper rifle.
  • New Neo City: "Neo-Japan".
  • No Ontological Inertia: Killing the Big Bad and destroying T'Leth makes all the remaining Zbrite inert, only good enough in large numbers, which is how they managed to send an Avenger to Mars for E-115 prospecting.
  • No Waterproofing in the Future: Weapons and other technology developed (or reverse-engineered) during the decades of fighting in UFO Defense are completely useless underwater, so, in Terror from the Deep, you must restart the researches from scratch. Consider it a Justified Bag of Spilling... that is, unless you're a clever enough hacker to exploit the similarities of the UFO Defense and TFTD engines and carry over goodies whose quantities were stored in the same data addresses. Partially justified by the fact that the alien gear needs Elerium, and the rest of the stuff is lasers. Still doesn't explain why they don't keep a few crates of lasers around for land missions, though.
  • Nostalgia Level: Just when you thought it was safe to go to the beach... The aliens will occasionally make landfall and start terrorizing resorts; this is when the game feels most like the original X-Com.
  • Obvious Beta:
    • It has a lot of crippling bugs. Xcomutil patched most of them, but you get goofy stuff like soldiers disappearing on 2-step missions if they get knocked out, base missions where you can't find the last alien, and the "Tasoth commander bug".
    • Additionally, there are nonsense impediments to some of the important research tree, which lead to more bugs, which aren't game-ending but still make no sense. You need a live Deep One to research Ion Armor (the equivalent of the Power Suit from the original game), so if you roll unlucky and aren't aggressive enough, you may not see ion armor (and subs) until very late in the game since Gillmen quit running terror missions after a couple months.
    • The "Updated Pathfinding AI" in OpenTFTD should make the Cruise Missions etc. a bit less tedious. Warboy discovered that the original algorithm wouldn't let aliens make two 90 degree turns, so that's why the game had so many "closet campers."
  • Ominous Floating Castle: In the game over sequence, the city of T'leth rises from the sea to work its magic on the human populace.
  • People Jars: Alien Autopsy reports feature the Alien remains in a liquid tank.
  • Phlebotinum Killed the Dinosaurs: The Colony ship T'leth crashing on Earth is what killed the dinosaurs.
  • Power Pincers: The Lobstermen have them, naturally, and they hurt like hell.
  • Punctuation Shaker: T'leth.
  • Pyrrhic Victory: Retroactively added in the Apocalypse manual, which states that the Destruction of T'Leth, in addition of killing your elite soldiers, releases the deadly chemicals that instantly kills everything in and around the Gulf of Mexico and turns the rest of the Earth into a toxic wasteland.
  • Rare Random Drop: Averted after the Elerium fiasco of the first game: the destruction of a USO engine does not necessary destroy the associated Zrbite, making it much more common (so much so that, in the early game, you can actually sell it if you're desperately in need of money, since you won't need it for a few months anyway).
  • Reactor Boss: The second part of alien colonies missions, and to lesser extent Artifact Sites, are too large to accomplish by killing every single alien, so it is more practical to find the synonium device that powers the base, destroy it while optionally capturing one of its high ranked guards, and get out.
  • Recycled Underwater
  • Red Sky, Take Warning: Not much has changed since the last game. The Geoscape is still where we spend most of our time, courtesy of a palette swap. The skies are burnt red (perhaps to indicate the aliens are playing hardball now).
  • Reinventing the Wheel:
    • Played With in the subsequent games: because TFTD was not developed by Microprose directly, the technologies from the game are not present in the later games: sonic and gauss weaponry is completely absent, with laser and plasma taking the forefront of XCOM weaponry. Zrbite is mentioned as becoming inert once T'leth was destroyed, possibly providing a Hand Wave, and the inert material becomes important in the development of the hyperdrive in Interceptor.
    • All this doesn't explain why you can't use the old hardware for surface terror missions, especially since the game disabled some of the heavier aquatic weapons, and you can't fly. Lasers would definitely be more useful than harpoons.
  • Reptiles Are Abhorrent: The Tasoth aliens are powerful vaguely reptilian humanoids.
  • Running Gag: A small one amongst veteran Terror players is that bases which see regular combat against the Lobstermen often requisition suspiciously large amounts of butter.
  • Sealed Evil in a Can: The Big Bad is one, not surprising since he is an expy of Cthulhu.
  • Sequel Difficulty Spike:
    • Early versions of the first game had a bug that enforced low difficulty mode - every time the player saved and then loaded the game, it would dial the difficulty back to the easiest difficulty. Due to complaints from high-level players that Superhuman difficulty was too easy, the sequel had the challenge rating cranked up across the board. In addition, while the first game only had one two-stage mission (the final assault), TFTD has many: ship terror missions, alien base attacks, and Synomium sites. And the last mission has three phases.
    • While most weapons in the game are simply equivalent versions of prior XCOM weapons made for underwater combat, there is no equivalent substitute for XCOM's laser weapons that had infinite ammo. All guns in TFD require ammo, which makes the item limit on your troop transport ships far more difficult to manage.
    • Bases are always staffed with a mixture of species, so it's not like you can run an early game Commander capture (not that you will survive a base assault in the early game, anyway). Furthermore, the sheer number of aliens in bases that have molecular control ability makes them nearly impossible to assault before you have your own MC lab.
    • Tentaculats, this game's version of the Chryssalid, is a much bigger threat. Unlike the Chryssalid, they can fly, meaning flying armor no longer protects your troops from them. This also means they can ambush your team by coming over walls and other various obstacles, making it much harder to spot them in time. Oh and every single Alien Colony and Artifact sight has several of them. Have fun.
  • Ship Level: Shipping lane attacks and cruise ship terror mission. They consist of two parts, above deck and below deck, like Cydonia. Plus numerous rooms, narrow corridors and lots of hiding places and you got a recipe for disaster.
  • Shock and Awe: Researching a Deep One reveals that their "acid spit" attack is actually a highly dangerous electrical discharge. It is the only attack in the game that armor is completely unable to guard against.
  • Shout-Out: TFTD is practically made of shout outs, if not direct ripoffs.
    • The Calcinites bear a laughable resemblance to the title antagonist of the B-movie Robot Monster due to them impersonating old-school divers.
    • The Tasoth race are pretty much Lovecraft's Deep Ones (even though there's an entirely different race in the game actually called "Deep Ones"), especially since their original description (which was replaced in the final version of the game) had them being converted humans (much like the aforementioned actual Deep Ones of the final game).
    • The Gill Men are extremely similar visually and thematically to the Gill Man of Creature from the Black Lagoon, as well as being very reminiscent of the Sea Devils and Silurians of Doctor Who.
    • The Great Dreamer, leader of the aliens, who sleeps most of the game away in the sunken spaceship/city called T'leth is, when you finally see him, an expy of Cthulhu, that giant monster/god dude who's slept away most of history in the sunken city called R'lyeh.
    • The Tentaculats are, visually, a copy of D&D Grells, but a lot of that sort of thing went on in the early '90s.
  • Space-Filling Empire: The Nations in 2040, including:
  • Super Soldier: The Lobstermen, who are extremely resistant to most types of weapon and the Tasoth, who aren't quite as tough, but simply have very high stats (on high difficulty levels, their stats higher than all but the very best human soldiers).
  • This Is a Drill: The game features a series of power drills that are the most effective weapons against Lobstermen. Combine with Molecular Control Disruptors to conserve ammo, or Thermal Shok Launchers/Thermal Tazers if you need to take them alive.
  • Too Dumb to Live: Just like in the last game, civilians in the terror missions just wander around aimlessly and completely ignore the aliens who are gunning them down.
  • Ultra Terrestrials: The Gill Men are a lifeform native to Earth. Research implies that they are a human ancestor that, instead of staying on land, ended up in the water. There's also a lot of evidence of genetic manipulation on the alien's part, so they're a human off-shoot in name only at this point.
  • Under the Sea: Half of TFTD is this.
  • Underwater Base: X-COM's base of operations. Also, one of the rarer terrain type in the USO recovery missions is a small series of underwater modules.
  • Underwater Ruins: Of several varieties. You can find sunken islands, sunken pirate ships (with gold! That you can't have), and even airplane carcasses.
  • Unwinnable by Mistake: The game was initially released with some brutal bugs in the research tree that could ruin a player's chances of finishing the game without them even realizing it. Thankfully, patches and mods have fixed some of these problems:
    • If a player researches a captured Deep One terrorist before researching a Deep One Corpse, Aqua Plastics, Plastic Aqua Armor, or Ion Beam accelerators, this will make it impossible to acquire Ion armor. Since the most advanced armor is needed to make a submarine that can reach the last level, this renders the game unwinnable.
    • If a player researches a Tasoth Commander before researching the final mission, this will not unlock it and will make it impossible to unlock since other commanders cannot be researched after this.
    • A "sub construction" item must be in your base stores before researching Zrbite and Transmission Resolver. If you research both of these without a sub construction item, there is a chance you won't be able to research sub construction.
  • Used Future: The Aliens seems to give this vibe.
  • The Very Definitely Final Dungeon: The Colony Ship of T'leth.
  • Vibroweapon: The drills.
  • Water Is Air: The Terror from the Deep was directly adapted from the original with no changes, so the characters are able to do ridiculous things like throwing grenades underwater. They also are unable to float or swim (instead just tromping around on the ocean bottom) until you research the equivalent of the flying suitnote . On the Geoscape, there are times where your fighter craft/troop transport cannot engage/deliver soldiers due to the (downed/landed) USO being "too deep", due to water pressure: even the most basic USO is capable of surviving depths that would crush a human-made submarine. Once you have the Leviathan, USO interceptions will never be called off due to extreme depth.
  • Zeerust: CRT monitors in 2040 and much more.
  • Xtreme Kool Letterz: The Sonic-Blasta Rifle and Thermal-Shok Bomb Launcher.
  • Zeerust: Running the X-COM nautical division in TFTD makes you feel like a regular Captain Nemo, particularly with the arsenal of pulp sci-fi weapons. The alien submarines manage to look antique and futuristic in equal measure.
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