Alien Submarines

The Alien Submarines used by the aliens of Terror from the Deep are big, blocky, shapes which resemble sea creatures and lack most forms of aerodynamics. They are able to dive and fly at breakneck speeds through the power of Zrbite and the resiliency of Aqua Plastics. Alien Subs come in a variety of forms ranging from the tiny Survey Ships right up to the massive Dreadnoughts.

Alien Subs are the aliens' sole method to move around Earth, and collect resources, so in theory, it would be possible to halt the alien advance if X-COM could maintain absolute naval superiority. Earth's forces do not initially have the resources required for such a task, and even if it becomes possible, the aliens have an vast resource supply and will not be set back by a war of attrition. In addition, alien undercover agents will continue to erode Earth's defenses from the inside.

Despite this, commanders should still down as many Alien Subs as possible. At the very least, it may slow the aliens down some.

UFOs are the equivalent in UFO: Enemy Unknown. The third game in the series, Apocalypse, introduced another fleet.

Alien Submarine Overview

Craft	Size	Max Speed	Accel.	Weap. Power	Weap. Range*	Damage Cap.	Crashed Pnt.	Destroyed Pnt.
Survey Ship	Very Small	2,000	12	0	0	60	50	100
Escort	Small	2,800	9	30	13	300	75	150
Cruiser	Small	2,600	9	25	35	300	125	250
Heavy Cruiser	Medium	3,800	8	60	20	450	250	500
Hunter	Medium	4,500	8	50	18	500	250	500
Battleship	Large	4,200	6	120	50	1,400	500	1,000
Dreadnought	Very Large	4,800	6	140	60	3,400	700	1,400
Fleet Supply Cruiser	Large	3,400	6	70	38	2,000	400	800

Comments:

• Weapon Range: figures given in the in-game UFOpaedia are a factor of 8 too high. The values in this table have been corrected so they are comparable to Sub Armament ranges.
• The Sub will crash if it sustains damage equal or greater to 50% of its damage capacity. A crash landing is the preferred outcome, since it permits a follow up USO Assault.
• The last two columns are the score awarded for crashing the Sub, and destroying it, respectively.
• Destroying a Sub is difficult, since it will crash land at 50% damage, so a destroying attack needs to take damage from below 50% damage capacity to 100%+ of damage capacity more or less instantly. In practice this means only small or medium Subs will ever be destroyed.

Weapons vs. Alien Submarines

Craft	Vmax
Barracuda	2400
Manta	4600
Hammerhead	4030
Leviathan	5800

Armament	Damage	Range (km)	Accuracy	Shots
Craft Gas Cannon	15	8	25%	200
AJAX	60	32	70%	6
D.U.P. Head	110	50	80%	3
Gauss Cannon	90	20	35%	50
Sonic Oscillator	150	55	50%	100
P.W.T. Cannon	200	60	100%	2

(See Quick Comparison Table for rate of fire, firepower and total payload information.)

If your craft is faster, the Alien Sub cannot escape; if your weapons have a higher range than the Alien Sub's, you'll be entirely safe from return fire.

• Sonic Oscillators can be used (even by Barracudas) with impunity against any Alien Submarines except Dreadnoughts. Even against Dreadnoughts, Sonic Oscillators are better than P.W.T. Launchers because a minimum of four P.W.T.-armed craft are required to down a Dreadnought.
• Single craft with dual DUPs (expected total damage = 396) are sufficient to bring down any Small or Medium Alien Subs. 3 craft with dual DUPs needed vs Fleet Supply Cruisers. DUPs cannot be used with impunity against Battleships or larger craft (unlike Xcom's Avalanche vs Terror Ships and larger).
• A single craft armed with dual Gauss Cannon (expected total damage = 2362.5) could expect reliably to bring down any craft, including a Dreadnought - provided it can survive long enough.
• A single craft armed with humble dual Gas Cannon (expected total damage = 1125) could also expect reliably to bring down any craft except a Dreadnought - again, provided it can survive long enough. (It will need to survive 40% longer than a Gauss Cannon-equipped craft, as the Gauss Cannon has 40% more firepower).

X-Com Subs vs. Alien Subs

• The Barracuda can always catch Survey Ships for the Barracuda is faster, but it often cannot dive deep enough to engage its target.
• The Manta is faster than all Alien Subs EXCEPT the Dreadnought.
• The Hammerhead can intercept all Alien Subs except the Hunter, the Battleship, and the Dreadnought, which must slow down in order for the Hammerhead to catch up.
• The Leviathan is 1000 speed units faster than even the mighty Dreadnought and can intercept all Alien Subs.

Quirks

• The floor maps & schematic pictures of the Survey Ship and Escort are swapped with each other in the Battlescape, the Interception window and the UFOPaedia.
• The schematic pictures of the Battle Ship and the Fleet Supply Cruiser are also swapped in the UFOPaedia and Intercept window. The floorplan maps on the Battlescape are not affected.