The first part of this series (hopefully) is based on the map pl_badwater. For those of you who don't play TF2 pl_ maps consist of a red team (defensive) and blue team (offensive). It's the blue team's objective to push a kart aka the payload (payload pl_, get it?) to the red team's spawn capturing points and receiving extra time on the way. Of course, it's the red team's job to stop them.
Let us examine the Engineer's arsenal:
1. The Sentry Gun
It's basically a missle turret that shoots ground.
2. The Dispenser
Remember in elementary school when the teacher gave out stars, or what have you, for good behavior in class and at the end of the week you got to pick out of a box with a bunch of candies and toys inside of it? This is that box. It provides health and ammo for your team as well as metal for the engis.
3. The Teleporter
Self-explainatory. Each of these items have 3 levels and with each level the item becomes more powerful / useful.
I will have detailed positions and intricately constructed diagrams below, but first let us examine the role of the defensive Engi.
RED
The red team's job is to hold ground, if the red team were a tree the engi would arguably be the trunk. Your job is to provide a central point around which your team can gather to defend. Generally if all SGs in the area go down your team will be pushed back, so I will stress that SGs are your absolute top priority. This doesn't mean that you should rush to get it first though, that is an amateur mistake most engis make! When the round begins the first thing that you should be putting down as red (after the tele entrance, of course!) is ALWAYS a dispenser. ALWAYS.
Why the dispenser?
Putting a dispenser down first ensures that you will have a supply of metal without having to run around once you've exhausted all the sources around you. Not only that, the dispenser only costs 100 metal and once it is finished you get an immediate +25, this gives you the option to build a teleporter exit straight away, or wait 10 seconds and put up an SG. Making a dispenser first will make the most out of the precious setup time that you have because engis are like probes, they can set something down to build and run off and do other stuff (but they can repair like scvs)! So you can put a dispenser down, run off to get metal, come back put down an SG and have enough metal to get it to level 2 asap!
After you get your dispenser and SG up, upgrade your SG to level 2 so it can defend you, your dispenser, and your teammates more effectively. After that you want to get your dispenser to level 2 and THEN put down a tele (note: this build is assuming minimal pressure from the other team). The reason for putting down the tele last is because it is essential that you setup and SECURE a point on the map since you are the defensive team and you MUST hold territory to prevent pushes.
What if you are facing moderate-high pressure?
If your sucky team is getting owned and your SG barely survived a run in with the other team with no end in sight, you need to get your SG to level 3 asap. (Sidenote: always save 100 metal to repair). Remember you are the tree trunk, of you get pushed back so do your branches~
What if your team sucks so badly that you died?
Take your tele back as fast as you can, if it died with you - run! Generally, if your dispenser is still alive, I would recommend trying to retake the position and get an SG back up because a level 3, even level 2 dispenser, will allow you to do that fairly quickly. If your dispenser dies and you die, chances are your SG will die before you get there or die shortly after because you will not have enough metal to repair it. Whether or not you want to go back is highly conditional.
What do you mean IF I want to go back?! I'm no coward!!
When both your dispenser and SG get owned and your team is getting pushed back because the other engis are incompetent, it's time to pull back and setup at another point. JLIG man, time is of the essence! You can't waste your time getting up a level 2 SG then getting steamrolled while killing only one guy. Use your teammates as fodder (that's what they are!) and pull back to secure another point while your team stalls their push. By the time they get to you, you'll have everything at level 3 waiting for them as well as some back-from-the-dead teammates.
So remember...
It's your job to hold vital points to halt the blue team's advance, you will hold like the strong Redwood and when you fall your seedlings will float to more fertile soil to grow again~
BLU(E)
Being a blue engi is a very dynamic job and everything you do will be highly situational so this section will be relatively short (I think).
In contrast to the red engi, the first thing the blue engi should construct is an SG. Why an SG? Because it's the only building that will survive out of the gate (literally LOL!). Putting down a tele will not help your team when the red team is waiting outside the gates for you, and a dispenser will most likely die before it can do any good - not that you need it that close to spawn anyway.
The role of the SG.
If you are on a good team you will be almost constantly on the move for the first few points, because of that you will most likely never get the chance or even need to upgrade your SG. That's a good thing because it gives you time to move your teles forward. You almost never EVER want to be making actual "offensive" SGs, it is a complete waste of time you WILL die. The point of an SG on the blue team is to be a safety net, you should construct it as close as possible without getting it killed before it can do anything substantial. SGs will essentially be a guard against counter-pushes that can undo a lot of hard work. You don't need to be the tree trunk, you are the roots that hold it when it sways~
I should never be aggressive with my SG?
Yes, you should, but there is a time and a place.
What happens when the push cain't push no mo'?
This is where you are needed the most and this is where you get to be aggressive. You should be actively moving forward teles for most of the round, but this is where you will need to put down a dispenser and SG and own some bitches. Here's the very important part, unlike the red team who will be mostly likely closer to their spawn, your team will be relatively far from where your push stalled and teles can only do so much. This is when you are going to need a well placed dispenser to provide ammo and health so they can outlast the other team. If there is a push stall, the dispenser is equally important for both teams (assuming your team doesn't suck and this is happening near the middle of the map). You should upgrade your SG to level 3 before you even dink! your dispenser because when you're stalling you want to stop any reds from trying to be aggressive and counter-push.
So remember...
You are the counter to the counter-push not the counter-counter-push (it makes sense, I swear!). Hold the line while your team does the rest, and remember to be active in moving buildings up.
+ Show Spoiler [Red Cap 1] +
A: This is a very temporary spot. Sometimes it can stall for a bit but you'll be overrun in about 5 minutes. The bright side is you'll get a lot of kills.
B: This is a decent spot, it's actually pretty important because it denies blue access to the high ground that overlooks the whole map and the tunnel exit.
C: This position has one job and one job only. Rain lead on the heads of the people pushing the cart. Unless someone has position D you shouldn't take this, even then people can still pick you off.
D: The rocks to the left of D draw a line to B and basically split the map in half. D is here to restrict pushes through the middle. You can catch some people when they are on top of the cap as well, but that's pointless by itself.
E: This is actually sub ground level, the beige you see is the roof to this little square room that's missing a wall. E is basically the last stand for cap 1, many times there will actually be two SGs and engis in there because it is so hard to snipe.
F: Marginal spot. Catches people as they exit tunnel. It can last a while with a good team though, don't underestimate it!
G: Bit of an after thought. I notice people use this sometimes, it's nice to catch people as they leave spawn but it's so open it will not last long at all. Though being on high ground helps.
+ Show Spoiler [Blue Cap1] +
To the right the awesome squiggle the spots are self-explanatory there are no dispensers because you usually push too fast to use them. Again, these aren't offensive SGs, they are just there to stop counter-pushes and pick off wannabe heros.
To the left is where the pushing usually stalls for a bit. Non-labeled items are, hopefully, self-explanatory.
A: I usually use this dispenser to level up the SG for B until it's 3 and move it there. Having to rebuild an SG is easier than having to rebuild an SG + dispenser.
B: This is a good spot (on the roof). Despite the SGs, angle it actually covers the large opening to the left of it to a good extent and it takes advantage of the choke to the right. The dispenser here is important, you absolutely need it to hold back ubered heavies which get owned by level 3 SG + dispenser.
+ Show Spoiler [Red Cap 2] +
If red has good engis and blue is slightly bad, round ends here.
A: My personal favorite spot. I usually skip trying to defend cap 1 altogether because if the other engis are bad it is a complete waste of time. Spot A is pretty decent at holding it's own ground, it covers both the cart, the most prominent entrance to the roof which I dotted in gray, and some area to the right of it. The dispenser goes right enxt to the a/c unit or whatever it is to protect it from sniping as well as to get teles on to the top of it.
A1: A slight modification of A, dispenser is the same but the SG is moved to prevent sniping by demos from the right. The downside is that it leaves your back exposed.
B: Plain and simple. Surprise missiles for cart pushers who aren't aware it's there, which they won't until it fires at them due to the position. Dispenser goes next to A's dispenser.
C: Second most favorite. You are completely covered from the back and you are covering the small stairs to the left as well as the main entrance. This is a really hard spot if they are pressuring because you are so exposed to the entrance. The dispenser I prefer to have behind me as I'm repairing but if they took a while to take cap 1 I will just put it where A/B put theirs so if my SG + I die my team can clean up and the dispenser will still live. The ammo next to it is crucial!
D: I don't like this spot because demos can get you from the back and it gives people coming from the main entrance too much room to maneuver before they are shot at. Covers same spots as C.
+ Show Spoiler [Blue Cap 2] +
Generally blue engis don't take the roof because if they do then they should have pushed red back already and will shortly anyway.
A: Usually you won't need these but if your team blows then, yeah, you'll need this. I don't have a preference as to which side because if I have to SG there it's kind of a morale killer anyway but the right side seems to give more cover and a place to put your dispenser if you need one.
B: I actually put B too far back but it's in the right place relative to the room! Dispenser and SG go there to stop red team from pushing into that little room and controlling it with an SG of their own. It's an ok spot to control as red but there are better places, I usually move here if I died to a spy or something and blue is close to or just captured the first cap.
C: Nothing much to say, once your team captures the room a dispenser here is helpful for your teammates to push out of the room.
+ Show Spoiler [Cap 3 Combined] +
This is probably the most impossible spot if red engis are good. There's only one way past this corner and that's suiciding into it.
A: Theres a small niche which I outlined with the dotted lines for a dispenser and an SG. It's not great by itself, but with B and C it's really strong.
B: This is my absolutely most favorite spot on this map because even by itself with no other SGs it is VERY strong. It's right around the corner, the dispenser is hidden you're entire team is usually there with you. It just wrecks the other team. Especially in combination with B and C.
C: C is great in combo with A and B but by itself it's quite horrible. Dispenser goes behind it relative to angle so you can take on heavy (the adjective) pushes and heavy (the class) ubers.
Squibbly is before (below) and after A is destroyed.
A: Dispenser here helps a lot. SG is optional and really is pretty marginal I think but it doesn't hurt. If you do build an SG it should be last thing you build here.
B: Dispenser behind it and SG just peeking over the corner. This really helps cap this point for blue, it's pretty open from second story of the building A is at though.
C: After you take down A you need to get C up asap, SG first. This stops red from counter-pushing and trying to retake A.
+ Show Spoiler [Red Cap 4] +
A: The left position here can hold by itself as it cannot be sniped from anywhere, so if your team sucks setup here. The right side can be sniped from above B. If you have more than 3 engis you can have 2 SGs setup here.
B: The upper SG position here is ok, not great as you can be sniped from above A by demos and from above C by everything. Again, you can have 2 SGs if you have more than 3 engis but the lower position here is open to above A, above C, and fairly open to cart so it's not great.
C: Not that great of a spot, more of a last resort or if you feel you are feeling too much pressure from the stairs. It can be sniped from above A and B though.
D: Crucial spot that a lot of people overlook, I drew in the little doorway there since it seemed out of proportion. Controlling this room leaves only one side open to attack and protects both A and C from sniping. As an added bonus if you position it correctly it can hit the cart as it starts it's decline into the final point.
+ Show Spoiler [Blue Cap 4] +
Really not much to say...
The left SG setup is great for stopping counter pushes people don't usually notice till they are hit. The SG on the right is setup in the room with one open window. It's ok, it helps stop harassment but that's about it. As a blue engi at this point you just want to get teles up and in good positions and watch out for spies.
That was pretty long. Whatever, take it like a man shorty.