Part of the Troops & Combat Series:
- Special Forces Engine: Energy Conversion Units and troop-building bonuses (You Are Here).
- Troops Guide Hub: Types, tiers and unit skills and combat roles.
- HQ Upgrade Requirements: The Plasma ladder that gates your slots.
- Buildings Reference: Barracks, Garage and Range, which the Engine sits on.
- Aircraft and War Vehicles: The other late-game machine track.
Quick Answer
The Special Forces Engine attaches to your troop buildings and buffs the troops that building trains. You install Energy Conversion Units into it, commonly just called gems.
The rule that shapes every decision here: an Energy Conversion Unit only affects the troop type of the building it sits in. A unit in the Barracks does nothing for your Riders.
Slots are gated by Plasma HQ level:
| Plasma HQ | Slots |
|---|---|
| P9 | 2 |
| P10 | 3 |
| P11 | 4 |
Later expansions added 7th and 8th slots, with the 8th unlocking set bonuses.
The stats a unit can roll:
- Troop Type Attack, Defence, Health, Lethality
- Final damage bonus for Heroes of that troop type
- Damage taken reduction from Heroes of that troop type
Two hard constraints worth knowing before you plan:
- No duplicate base stats in one building. Two units with the same base stat cannot both be installed in the same troop building.
- Refining consumes three. One unit is the target, two others of the same level and base stat are consumed to raise it.
Should you care? Only at Plasma HQ. If you have not reached P9, this system does not exist for you yet.
Overview
This is one of the clearest examples of the game's late-game design: a system that only opens once you are deep into the Plasma ladder, and which then quietly becomes one of the larger troop stat sources available.
What you'll find is that it rewards the same discipline everything else in this game rewards, which is specialisation. Because units only buff the building they sit in, an account running one dominant troop type concentrates every unit it owns into one Engine. An account running all three splits its units three ways and gets a third of the benefit in each.
Here's the framing that matters for planning. This is not a system you drift into. The slots are gated by Plasma HQ levels that take months, the refining is destructive, and the duplicate rule means you need a plan for which six or eight stats you actually want before you start refining anything.
How the Engine Works
The Engine is applied to troop buildings: your Barracks for Infantry, Garage for Riders, Range for Hunters, as covered in the buildings reference.
Each building has its own Engine with its own slots and its own installed units. The bonuses apply to that building's troop type only.
That containment is the whole strategic content of the system. Your dominant troop type should receive essentially everything, and the other two Engines can sit near-empty without much cost, because you are not fielding those troops in numbers anyway.
[!IMPORTANT] If you have been running a mixed army, this system is a strong argument to stop. Slots and units are scarce enough that spreading them across three Engines produces bonuses too small to notice in any of the three.
Slots and the Plasma Gate
Slot count tracks your Plasma HQ level:
- P9 gives 2 slots
- P10 gives 3 slots
- P11 gives 4 slots
Later updates added the 7th and 8th Energy Conversion Unit slots, and the 8th slot unlocks set bonuses between units, which is the point where the system stops being additive and starts compounding.
Two planning consequences.
Slots arrive slowly. Each Plasma level is a substantial project, so you will spend a long time with fewer slots than units. That makes refining more attractive than hoarding, since a smaller number of stronger units beats a pile you cannot install.
Set bonuses are an end-state target, not an early consideration. Do not plan a stat spread around them until the 8th slot is realistically in view.
Energy Conversion Units
The six base stats
| Stat | What it raises |
|---|---|
| Troop Type Attack | Damage dealt |
| Troop Type Defence | Damage reduced |
| Troop Type Health | Damage absorbed before dying |
| Troop Type Lethality | How much damage converts into kills |
| Hero final damage (that type) | Hero-side damage output |
| Hero damage taken reduction (that type) | Hero-side survivability |
The first four map onto the four troop attributes that decide combat: attack against their defence, lethality against their health. The last two are hero-side lines, which stack with what Tempest Arms provides rather than duplicating it.
The duplicate rule
Two units with the same base stat cannot be installed in the same troop building.
This is the constraint people discover late and resent. It means your Engine is not "four copies of the best stat"; it is a spread, and you must decide which distinct stats you want occupying your limited slots.
For most accounts the sensible reading follows the same logic as alliance battle tech: survivability first on Infantry, damage first on Hunters and Riders, since Infantry take the hits and the others deliver output.
Refining
Refining raises a unit's base stat. One unit is the target; two others of the same level and same base stat are consumed as materials.
Three-for-one is steep, and it is why the duplicate rule is less painful than it first appears. Duplicates are not waste; they are refining fodder for the copy you intend to keep.
[!WARNING] Do not refine before you have decided your stat spread. Refining is destructive and three-to-one, so raising a stat you later decide not to install is an expensive mistake at this stage of the game.
A Sensible Approach
For an account arriving at P9:
- Decide your dominant troop type, if you somehow have not already.
- Fill that building's slots first, with distinct base stats.
- Keep duplicates as refining material rather than installing them elsewhere.
- Refine toward a small number of strong units, since slots lag behind supply.
- Ignore the other two Engines until your main is genuinely full.
- Plan for set bonuses only when the 8th slot is in sight.
F2P vs Spender
F2P accounts reaching Plasma at all are doing well, and the correct approach here is narrow: one troop type, distinct stats, duplicates fed into refining. The system is slow rather than closed, and because units are permanent it rewards patience more than most late-game tracks. Do not divert biocaps toward it while march slots or hero completion are outstanding.
Spending accounts can populate multiple Engines and reach the 7th and 8th slots meaningfully sooner, which is where set bonuses turn a linear system into a compounding one. Even here, concentrating on one troop type first produces a better fighting account than spreading evenly, because combat resolves through one march at a time.
Common Mistakes
Installing units across all three buildings. They only buff their own type. Fix: concentrate on your dominant type.
Trying to stack the same base stat. Not permitted in one building. Fix: plan a spread of distinct stats.
Treating duplicates as waste. Fix: they are refining material, three-to-one.
Refining before deciding the spread. Destructive and expensive. Fix: decide, then refine.
Planning around set bonuses early. They need the 8th slot. Fix: ignore until it is in view.
Expecting the system before Plasma. Slots start at P9. Fix: finish the HQ ladder first.
FAQ
What is the Special Forces Engine in State of Survival? A system attached to your troop buildings that buffs the troops each building trains. You install Energy Conversion Units into it to raise that troop type's stats.
How many Energy Conversion Unit slots do I get? Two at Plasma HQ P9, three at P10, four at P11. Later updates added 7th and 8th slots, with the 8th unlocking set bonuses.
Do Energy Conversion Units buff all my troops? No. A unit only affects the troop type of the building it is installed in. A Barracks unit does nothing for Riders or Hunters.
What stats can Energy Conversion Units have? Troop Type attack, defence, health and lethality, plus hero final damage and hero damage taken reduction for that troop type.
Can I install two units with the same stat? Not in the same troop building. Duplicates are best used as refining material instead.
How does refining work? One unit is the target and two others of the same level and base stat are consumed to raise it. Three units in, one improved unit out.
Should I spread units across all three troop buildings? No, unless you genuinely field all three types in strength. Concentrate on your dominant type; a third of a bonus in three places is worse than a full one in one.
When does this system unlock? At Plasma HQ. If you are below P9 it is not available to you yet, and the HQ ladder is the path there.
Key Takeaways
- The Engine sits on troop buildings and buffs only that building's troop type.
- Slots by Plasma HQ: P9 = 2, P10 = 3, P11 = 4. The 8th slot unlocks set bonuses.
- Units roll troop attack, defence, health, lethality, plus hero final damage and hero damage reduction.
- No two units with the same base stat in one building. Plan a spread.
- Refining is three-to-one: one target, two same-level same-stat units consumed.
- Duplicates are fodder, not waste.
- Concentrate on one troop type. This is the strongest specialisation argument in the game.
- Nothing here matters before Plasma HQ.