Welcome to my guide (updated since the September rebalance) on the how-to-use UKF emplacements. In this document, I'm going to cover some basic information about each emplacement type along with specifics about correctly orienting your emplacements to best kill the Huns while not getting you killed.
Why should you care about this? Well, most players don't have a replay where they have a kill/loss ratio of 130+/0. You read that correctly, 130+ (I believe it was 133 actual) with 0 (yes, ZERO) losses. I've been able to accomplish this particular zero death scenario at least a half dozen times. And yes, I'm aware that the game doesn't reward such canny play, but really it should.
Section 1: Mortar Pits
In our first section, I'm going to discuss the universally available emplacement, the mortar pit. Weighing in as a tier 2 emplacement (meaning that it requires a previous upgrade to be constructed), the mortar pit is constructed by Royal Engineers (that are produced from the Platoon Command Post-PCP) and costs 400 manpower. It has the Creeping Smoke Barrage (free to use, shares a cooldown with the mortar barrage) at veteran level 1, and the mortars will fire faster if the emplacement is garrisoned.
The mortar emplacement is roughly square in size and is shaped like a pair of brackets [ ] with access points on both ends. While conventional logic would suggest that you place the sandbagged sides toward the enemy, the mortar emplacement is rather unusual in that your the garrisoned units are almost never able to face directly over the sandbagged sides. The mortar teams' use line of sight to fire (the mortar teams try to engage enemies firing at them) so they orient toward attacking enemies.
To get around this little quirk I suggest orienting the entry points where you expect enemy units to attack. This is actually a nifty trick because it allows the garrison to set up on any of the 4 points closest to the entrances which gives effectively 360 degrees of covering fire.
Because mortar pits are pricy (in terms of manpower), they're not the type of emplacement you're going to want to use to block an expected enemy axis of advance. At veteran level 3, they are upgraded with improved durability but expect them to be destroyed by tanks relatively quickly; so mortar pits are better suited to being placed in spots that might be a bit harder to reach for enemy vehicles.
They have much better range than any of the mobile mortars and are really only outranged by actual artillery. On smaller 4v4 maps (where the UKF really shines), you can cover half the map with just 2-3 mortars so don't under-value these late game; knocking an enemy off that VP that's just in range and preventing a capture can really turn the last few minutes toward victory rather than defeat.
Section 2: QF 17-Pounder AT
For section 2, I'm going to discuss the other universally available emplacement the Quick Fire, 17-Pounder Anti-Tank emplacement. The QF-17 (as I will hereafter refer to it) is a hefty Tier 3 (requiring both the PCP and Company Command Post-CCP) mid/late game emplacement. It has a moderate rate of fire and is the only UKF anti-tank that is absolutely certain NOT to bounce off of German armor. The QF-17 has the ability to load Piercing Shot (90 munitions) at Veteran 1 and can fire a flare (40 munitions) when there is a garrison unit.
The QF-17 emplacement is a large, circular emplacement with 4 sandbag walls and 4 openings. If I'm going to spend the pop-cap to garrison the QF-17, I'll put in a royal engineer squad with the anvil upgrade (which grants them the extra Vickers K, light machine gun) and an extra LMG and either a light AT or flamethrower captured from the germans. The QF-17 is a heavy emplacement and while it will eventually crumble to AT and indirect fire, it can sustain a tremendous amount of punishment before falling.
Much like all other anti-tank weapons in CoH2, you want to place your QF-17 Emplacements with as wide-open fire-lanes as possible. The QF-17 isn't directionally limited so for maximum value try to find as many angles of that 360 degree arc to open up for long-range hurting. I will often use the attack ground feature to ensure my fire lanes are open and anything the AT gun doesn't destroy but seems to block line of fire can be cleared by Engineers (other than buildings, even destroyed they can cause interference, so try to avoid them).
Because it is the heaviest emplacement, you'll want to build them to cover choke points for armor as well, with interlocking fire from mortars (to clear away pesky indirect fire) and cover them with HMGs placed in buildings or trenches to keep away the light AT and flamethrowers.
Section 3: Bofors QF 40mm Emplacement
In section 3, I'm going to discuss my personal favorite emplacement, the Bofors QF 40mm Anti-Aircraft emplacement. As it saw considerable service during WW2 as an AA gun, in CoH2, the Bofors definitely can (and will) shoot down pesky enemy aircraft; where you'll get the most utility however is as a light AT emplacement. Unlike the other emplacements discussed so far, the Bofors is an optional emplacement. That is, when you hit Tier 2 (after building the PCP), you'll be presented with the option to build Bofors guns or armored cars. Another difference is that the Bofors does not have a veteran special ability; it does have the ability to fire a Suppressive Barrage (longer range, indirect fire) when garrisoned.
The Bofors QF 40mm is a circular emplacement with 3 sandbag barricades and 3 openings. Since garrisoned units can only deploy in the middle of the sandbag walls so you'll want to point the walls rather than the Bofors cannon itself toward expected enemy approaches. The Bofors emplacement is a medium strength fortification and will crumble if attacked at any length by AT or tanks. That said, the Bofors is a very versatile emplacement and, if backed up by a royal engineer squad can actually destroy much heavier opponents if it can get shots on side or rear armor.
I like to use Bofors guns as a catch-all in any location where I'm not expecting Panthers or heavier armor. Like the QF-17, the Bofors has a 360 field of fire and I like to put them near crucial VPs as the 40mm cannon fires much more rapidly than other emplacements and it will chew up both infantry and light/medium vehicles.
Section 4: Miscellaneous Emplacements
In section 4, I'm going to cover the remaining constuction that can be considered "emplacements". There are really three additional constuctables that can be considered emplacements: the trench, the sandbag wall and the forward headquarters (FHQ). Each of the three serves a special function and can contribute toward victory in its own way.
First, the sandbag wall is a simple, light-duty, green-cover-generating dirt wall. They are quick to build, free and will stop most light vehicles from passing. They're constructed by the infantry sections, rather than by royal engineers and represent an easily-flanked, easily-destroyed, temporary time-buying measure. You can block bridges with them to keep non-infantry from crossing (and if used with barbed wire, it will stop non-engineer infantry temporarily). Other applications that I've used it for: 1. traps... players will typically just order units to climb over sandbags, drop a mine right behind the bags on your side and retreat before grenades get tossed over. 2. hull-down... with a little practice, you can build them right next to vehicles, this creates green cover for some of the vehicle and the sandbags will absorb some of the incoming damage 3. trolling... fun to troll friends and AIs. If you happen to disable a non-tank vehicle (like a kubelwagon, or other half-track) if you build the walls right up against 3 sides and leave a tiny gap, the infantry will get in the vehicle and it will be trapped unable to turn or run over the walls.
The trench is an emplacement that I don't use that often. Trenches cost 50 manpower to build and are relatively durable. They provide green cover to most attacks but are extremely vulnerable to flame attacks. Unlike previous CoH titles (and most other constructable short-term defenses), the trenches are the property of the building player and are treated like a building. The AI will stop to attack them (if using attack/move) and the AI players destroy them religiously. The most common use for them is temporary defensive points although they're useful to have near other emplacements if you want to keep a squad from getting hit by indirect fire. The main thing I use them for is early warnings as they get fired upon and report like a building being attacked (they also have a rather limited but sometimes useful small line-of-sight capabiliity, when not garrisoned).
The FHQ is a very useful non-combat emplacement. It costs 250 manpower to build and (as long as you're within connected territory) it acts as a reinforcement point AND will activate the garrisoned ability of any nearby emplacements. The FHQ has two active options: 1. For 200 manpower, it will add the ability to act as a retreat point with an on/off toggle. 2. For 45 munitions, it has a Coordinated Barrage. The Coordinated Barrage ability is a "danger-close/broken arrow" ability, which means that it's intended to slow the enemy attack by bombing your own position. I never use this ability, for two reasons. First, I find that when I'm at a point where the enemy is in range of the ability, I'm already falling apart and almost never have enough munitions to activate it. Second, I usually forget it's there.
In closing, I hope that you've found this guide informative. I've written it 10 September, 2015 after a considerable number of games played using the UKF. If I get positive response (or the urge to write more) I will consider putting together a similar document outlining the commanders and best practices to get the most from them.
Anyone interested in my successes in zero loss battles are welcome to request my replays and I'll try to accomodate that as I can. The best victory in that regard to-date was a 4v4 vs hard comps and resulted in 133/0 kills/losses.