Deep One

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General Information

Deep One
Deep One

The Deep One is a biological nightmare, a cross breed, produced by the mind warping experiments of the Aquatoids. We have encountered several variations of this creature.

After extensive research we conclude that these are manufactured by the invaders. Swelling their ranks when fresh human stock has been captured. Each of these sub-human is armed with an electrical energy discharge powerful enough to kill an aquanaut.

Source: Terror From The Deep Ufopaedia

Deep One Autopsy
Deep One Autopsy

The creature is a graft of man and alien organism. The human brain is massively altered to accommodate control electronics and the Alien cortex. All vestiges of the human body seem lost save one: the eyes. The surgical graft appears to allow the alien foetus to consume the human host as it grows.

The tough skin of the creature appears to be a non-organic, metallic mesh, extremely strong and flexible. The resulting cross breed is strong, fast and utterly under the control of the aliens.

Source: Terror From The Deep Ufopaedia
Deep One
Time Units 50 - 74
Health 35
Energy 90 - 133
Reactions 55 - 75
Strength 40 - 50
Bravery 90
Firing Accuracy 20 - 81
Throwing Accuracy 58
MC Skill 0
MC Strength 50 - 62
Front Armour 3 - 9
Left Armour 2 - 7
Right Armour 2 - 7
Back Armour 1 - 4
Under Armour 4 - 14
Hidden Attributes
Melee Accuracy 70 - 104
Energy Recharge 30
Victory Points 12
Standing Height 21
Kneeling Height 16
Intelligence 4
Aggression 2
Other information
Armour category Deep One
Possible Ranks Terrorist
Unique Attributes Arcing Projectile Attack

Deep-Ones are a graft of a human body and alien technology, with armored skin and alien implants to control them. The eyes are the only organ left unchanged, although it's hard to tell under the red glowing goggles.

The Deep-One is a terror weapon associated with the Gillman race. They are primarily brought into battle on land mission. This includes port attacks, ocean liner attacks, X-Com aqua base attacks and island resort attacks. They will appear underwater only during the T'leth mission, which is also the only time that Gillmen aren't present alongside them.

Deep-Ones are armed with a long range arcing weapon. Though they pose little more threat than the average Gillman or Aquatoid, their electric attacks are not to be underestimated, as they can be fired over walls and can deal massive damage to any human targets not wearing Ion Armor or better.

Note: Though the Ufopedia describes the Deep One as having an electrical energy discharge, the weapon is functionally a Gauss weapon and uses the Gauss damage modifiers.

The Deep-One is a crucial alien in X-Com's overall research. The corpse reveals the fundamental principles behind the Aqua Plastics and Plastic Aqua Armor. Only after you've learned this will interrogating a live Deep-One allow a better understanding of constructing the more potent Ion Armor. The Ion Armour and its upgrade, the Magnetic Ion Armor are an integral part of Sub Construction. Deep-Ones are also an optional lead to understanding MC technology.

The only way to capture a live Deep-One is to get them during a Gillman land based attack. Gillmen tend to appear for a short window of time and appear less often as the Lobsterman and Tasoth crews become available. It is best to be aggressive and engage and capture a Deep-One as soon as possible, even at the risk of abandoning the terror site if it's too difficult. Not capturing one early may result in a very long wait before you can find another.


Deep Ones are not particularly dangerous. While resilient to harpoons, most weapons will kill them easily.

The greatest danger to your Aquanauts comes from the Deep Ones' ability to attack over walls, or from angles not available to other weapons. You may try flushing such Deep Ones out of cover with explosives, but this may end up causing significant civilian casualties if you're not careful. The weapon itself can cause heavy damage to aquanauts wearing the strongest armor due to the high base damage. It does reduced damage to Coelecanths and Displacers.

The Deep Ones' biggest weakness is their inability to use reaction fire. This means they are completely unable to harm you during your own turn. Feel free to run up to them and kill them with melee weapons if there are no other aliens around. NOTE: This is not true in OpenXcom, where Deep Ones use reaction fire normally.

Research Bug

The TFTD Research tree has a few bugs. One major bug that will prevent you from winning the game is associated with the Deep One. Researching the Deep-One in the incorrect sequence will prevent you from getting the advanced armor and most importantly the subs. The advanced subs are one half of the necessary requirements to launch the end-game mission.

To avoid it, you will need to research the live Deep One in the proper sequence. This proper sequence is covered in The Deep One Dilemma article.


The following are some miscellaneous notes on the Deep One:

  • The Deep One takes 0.8x damage from explosions and 0.9x damage from Armour Piercing, Incendiary and Gauss attacks, but 1.1x damage from Sonic weapons and 1.2x damage from Melee attacks.
  • They appear almost exclusively on land, and are normally replaced by Xarquid when underwater. They are encountered underwater only during the T'leth mission.
  • Their weapon is an innate weapon that has a grenade-like trajectory and cannot be recovered. It makes the Deep One look as if it is spitting something at your Aquanauts.
  • Despite being required for researching armour, Deep Ones have weaker armour ratings than the Diving Suit!
  • Do not confuse the Deep-Ones for the Lovecraftian Deep Ones,which are more closely related to the Tasoth than TFTD's Deep-One.

See Also

TFTD Badge Terror From The Deep
Aliens AquatoidGillmanLobster ManTasothMixed Crew
Terror Units Bio-DroneCalciniteDeep OneHallucinoidTentaculatZombieTrisceneXarquid
Data TFTD Alien StatsAlien Rank TFTD Damage Modifiers TFTD Alien Appearance Ratios • SWS/Terror Unit Innate Weapons