The "Micro" Placement, the positionning of the sentries in a room, will depend on 2 factors:

• The use: you want them
  • to cover a single point (example: phase gate)
    
  • to cover a lane/ huge space (an intersection/ room)
  
  
• the number of sentries you can afford or want to place (1, 2 or 3). You would prefer to go 3, since they cost 25 Tres (Team Ressources) when 1 sentry costs 15 Tres. 2 Sentries is usually a good number to support gates.

A sentry, as i wrote it in Notes & Numbers, has a 160 degree vision. DO NOT waste it. 10 More degrees can be the 2 bullets needed to end a fade's life. Even a single degree can make the difference.

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In this example, the red angle shows a portion of the sentry's vision going in the wall, wasted. In the second picture, you can see the angle you saved when placing it in a better position.

• Use the geography of the room to your advantage. Put all the sentries you can back to the wall, so:
  • They can cover more space of the room
    
  • They can't get bitten from behind by a skulk, so it is safely covered by the other sentries.
• Make the sentries face all the corners possible. Aliens will always use the corners to turn, enter or flee the room (low fades will try to hide behind corners). A certitude: Aliens use corners, so cover them (Check my exemple of Central sentries (Caged) on the macro section).

When you place sentries, unexperienced players tend to do a lot of mistakes.

One of them is the covering management. Sentries are expensive, and are supposed to live (in most of the cases) without any marines nearby. In this goal, the sentries have to cover each other and the battery. If a skulk gets behind a sentry that isn't covered by another one or behind a battery uncovered either, here goes your 25 Tres.



Here is an exemple of 3 sentries covering each other, in what you can call a triangle formation:
















But by doing this, it is impossible to make the 3 sentries face 1 direction out of the inner sentry circle. The only way to do this is to use correctly the geographical circumstances of the room. It's very hard to pull out, and requires high geographical knowledge. You can check my sentry placement on Caged in the "Macro" section to have an idea of it.

Again,a way to get your sentries covered easily, is to place them back to the wall (use the geography).This way, the skulk wont be able to hide behind it to preotect it's self from other sentries/marines.

Sometimes, there will be rooms with constant fighting and constant marine presence. In these kind of cases, your sentries wont require a cover and will be able to fully use their fire power: battery behind, all sentries at the front. A battery at the front can even block a sentry's line of sight sometimes.










For example, Dome. This room, in a lot of situations, will be under constant fighting (so constant marine presence). Thus, no need to cover the back of the sentries and this way the fire power is maximized.

2 Sentries is a good number to support gates:

• Costs less in Tres and supply than 3 sentries
  
• Is enough to cover a gate while covering themselves (with good wall usage).

Negative points:

• they wont cover a lot of space
  
• they wont damage lifeforms a lot
  
• they will still cost 20 Tres and 25 Supply.

Here is how to cover a gate with 2 sentries using a corner:


If you observe it well, you will notice that the sentries cover:

• Each other
  
• The battery
  
• The PG

As i specified in the guide description before, sentries aren't placed randomly, nor on the map nor on the timeline.

Sentries will play a "Macro" role in only if they fullfil these 2 conditions:

• When they are used before PGs (Phase Gates), because once PGs are up, rotating as a marine becomes way faster and holding lanes with sentries wont hold any meanings anymore.
  
  
• When they are used to protect/deny a lane, to cover your RTs/ deny aliens' RTs. When sentries are placed to defend a room for a PG or, even before they are researched, to protect your base or an ARC settlement, they only play a "support" role.

• When going early sentries, you can place the robo under the power-nod of your base, forcing the skulks to expose themselves to the rifles when they bite the power-nod if they rush your base.
  
  
  
  
  
  
  
  
  
  
  
  
  
• When dropping sentries in a non high-skilled team, dont hesitate to remind your marines to fight in the line of sight of the sentries. Sometimes, even good players forget them for 1 second and end up being killed, with your sentries wasted.

For the following sections, i will use this Legend to show the angle covering:

These sentries will be used for defensive purposes. Unlike the aggressive sentries, who will be placed far into the map.

When you think about defensive sentries (on the macro scale), you think about the lanes you cut and the number of RTs inside these blocked lanes. Getting sentries is useless if it is to hold your naturals.

Sentries dont move, so when they lane, You must make sure there are no vents or ways aliens can use to get behind.

They are not only a way to get a better defense, but it will also allow you to have less marines laning and more pushing RTs, as a compensation for late armor 1.


-A spot on Central, Caged (Versus Sewer/Ventilation start)

........In the Document#2 (top right) you will notice that the three sentries cover each other but manage to have a maximized fire power on the principal hallways. This is thanks to the perfect geography of the room, with the corners and containeers used to protect the back of each sentries.

You will also notice the corners, that i managed to cover with 1 or 2 sentries each time. As i explained before, corners are where the lifeforms will always pass or flee, so the best thing to have in line of sight.

-A spot on Access Alpha, Eclipse (Versus Computer Core/ Maintenance start)



Note: an RT produces 10 Tres/minutes (1 Tres every 6 seconds)

40 Seconds Tres calculation:

60 Tres (of the start) - 27 Tres (35 Tres of the Sentries+ robo, -8 when robo is recycled) - 20 Tres (Naturals built) -20 for the other covered RTs by the SEntry/marine ane blocking -10 Tres for the few medpacks (approximation)+ 10 Tres produced by the RTs built before the 40 seconds mark

This means that at 40 seconds, you have 0 Tres but 5 rts (sometimes 6) and an effective lane block.
Res production: 50 Tres per minute.

At this point, you have 2 choices:

• Get 1 ip before the arms lab, to keep constant pressure
  
• Get an arms lab and get Armor 1 as soon as possible.

If you choose to go armor 1= 20 Tres (arms lab) + 20 Tres (Research Cost) + 75 Seconds (Research Time)

At 40 Seconds, you have around 10 Tres. Arms lab can be build 10 seconds later. Then, time needed to start Armor 1 Research = 24 seconds (20 Tres will need: 3 Tres per 6 seconds, so (20/5)*6=24)

Conclusion: Going fast defensive sentries and capping naturals will allow you to get Armor 1 at 150 Seconds (40+10+24+75 seconds) and to hold 5 to 6 RTs, compared to the 95 Seconds of the Classic tech path time. Difference: 55 seconds. But you end up with 5 constant RTs (depening your lane) and sentries to lane.

The goal of these sentries wont be to hold anything, but to cut aliens from everything. "Everything" refers to all their RTs (ressource towers), limiting them to a maximum of 2 RTs. These sentries, as always, will depend highly on the map and travel distance of marines. Since you wont have a lot of RTs and delayed upgrades, getting 1 more IP (Infantry Portal) can usually help a lot to keep your pushes constant and your RTs defended.

In certain Situations, they will not only cut aliens from their RTs but steal them. Sentries in NanoGrid on Veil is one example.

These sentries, as you all probably guessed, are extremely risky since they are built deeply into the alien territory, and by marines who have no upgrades (you dont cut lanes once aliens have 2 hives...).
But "who risks nothing gains nothing". Placing succefully these sentries is usually a win, even if you dont have a lot either (they will have less). Nonetheless, they will only work if your marines can stay alive a good time. Do not try it with low skill teams.

What you have to be aware of:

• The risk to loose nearly all of your marines + sentry res (ressources) if it fails, without talking about getting very late in the tech path.
  
  
• The risk of skulks baserushing while nearly all your team is required to place these sentries far from your base. always have 1 marine capping each of your naturals while the rest of your team is doing the teampush to place the sentries, so that 1) you get 3 rts and the sentries and 2) you have 2 marines ready for a baserush, that can take care of it or gain time until the team comes back.
  
  
• The sentries have to cover each other as much as you can, since there is a high risk that all the marines will die.
  
  
• Always check the alien spawn, because as i stated it highly depends on their spawn, but also check if they didnt drop a fast hive.These sentries become totally useless if aliens get 2 hives.

-A spot on North Tunnels, Tram (Versus Warehouse start).
These sentries cut warehouse from plateform, limiting aliens to 2 RTs if you succeed placing them fast enough.
If you zoom on the doscument #2, you will notice a blind spot on the left of the sentry from below. It is a proof that it is very hard to make 3 sentries face 1 direction and cover each other at the same time, and it requires very special geographic situations.
If you are familiar with this room, you will also notice that the top sentry is back to a containeer. It's a very good way to cover it's back, limiting again the number of blind spots aliens can use to destroy the sentries without dying.

-A spot on NanoGrid, Veil (Versus any starts).
Some will say "But you can bile bomb it from the vents" it is true, but i remind you again: aggressive sentries are very early in the game, and you have to set them up before aliens even cap NanoGrid (or when they are trying). If it succeeds, you will have an extremely large area covered, aliens' naturals denied and capped, and 1 marine will be enough to hold this room with these sentries.

In this example, You always have to come from the opposite side of the alien spawn (go from West Junction if they start Pipeline, and vice-versa. Always send a marine to the opposite natural of your team push direction (if your team goes West, have 1 or 2 marines going topo) so that you can cap an RT even if the push fail and so you have marines ready for an alien baserush.

Deeper in the game, when bile bomb will be up, you will have to find a different placement, far from the vent,if you ever want sentries. End game, you would prefer to keep Structure Supply for ARCs or Tres for Jetpacks.


Note: an RT produces 10 Tres/minutes (1 Tres every 6 seconds)

40 Seconds Tres calculation:

60 Tres (of the start) - 27 Tres (35 Tres of the Sentries+ robo, -8 when robo is recycled) - 20 Tres (Naturals built) +8 Tres produced by your main RT + 2 Tres produced by the 2 naturals for the past 10 Seconds -10 Tres for the few medpacks (approximation)

It means that at 40 seconds (or a little bit more) you have: Sentries at North tunnels (limiting aliens to 2 RTs if cyst cut properly), your naturals (total of 3 RTs), and 13 Tres.

At this point, you have 2 choices:

• Get 1 ip before the arms lab, to keep constant pressure
  
• Get an arms lab and get Armor 1 as soon as possible.

If you choose to go armor 1= 20 Tres (arms lab)+ 20 Tres (Research Cost) + 75 Seconds (Research Time)

At 40 Seconds, you have around 13 Tres. Arms lab can be build a few seconds later. Then, time needed to start Armor 1 Research = 40 seconds (20 Tres will need: 3 Tres per 6 seconds, so (20/3)*6=40).

Conclusion: Going fast agressive sentries and capping naturals will allow you to get Armor 1 at 170 Seconds (45+40+75 seconds), compared to the 80 Seconds of the Classic tech path time. Difference: 90 seconds.

It is on the long term still faster upgrades for marines, since again aliens wont even have 3 RTs, with lerks/upgrades delayed even more.

-Costs Tres to build:

• 10 Tres (Team Ressources) per Battery
  
• 5 Tres per Sentry

-Maximum to build;

• Maximum 3 Sentries per Battery.
  
• Maximum 1 Sentry Battery per room.

-Costs Team Supply:

• Battery: 15 Supplies
  
• Sentry: 10 Supplies

-Sentry requires a Robo-Facotry.
-Sentry operates on Battery power only.
-Battery operates even without power in the room.
-Sentry can be confused by Spores and Stomp.
-Sentry's field of vison: 160 degrees.
-rotation speed when alien detected: 60 degrees/second.
-Sentry's damage: 5 per shot.
-Fire rate: 1 shot/ 0.15 seconds.
-Confused fire rate: 1 shot/2 seconds.
-Range: 20 units (marine's speed: 5.25 units/ second).
-The sentry will be ready to fire 3.5 seconds after it is built.
-Sentry's solidity: 500 health + 100 armor.
-Battery's solidity: 600 health + 200 armor.