Note that I will be referring to ideas discussed in this article.
In brief, let us define three kinds of ways to use movement for the purpose of drawing firepower onto an enemy. "Open" is when your enemy comes into your firing lanes, "closed" is when you bring your firing lanes into your enemy, and "static" is when your firing lanes require no movement (This is usually achieved through indirect fire).
Let us look through the forces available to an imperial guard commander and compare them to the above systems of application of firepower.
In general, units that want to engage in open traps must have a few things in common. The first and foremost principle is that weapons should be of long range, or else an enemy unit may be safe even if in line of sight, defeating the purpose of an open trap. As well, a unit engaging in open traps need not have a tremendous amount of mobility (as movement on your part is not regarded in an open trap), thus heavy weapons are generally best suited to open traps.
Command Squads: In general, the command squad is not the prime candidate for an open trap. Not only can they sport only one heavy weapon, but as well it generally requires that an officer be placed in a position of danger, or at least in sight of an enemy. The one advantage of using command squads for open traps is that they are relatively logistically inexpensive to field. In the end, though, their price is equivalent to a Sentinel, which can hold most of the same weapons, but do so with armor, and while having the ability to move and see over various forms of impeding terrain.
Heavy Weapons Squads: These units are a prime example of a unit devoted to open operations. For their price, they can field the most heavy weapons, making them a very economic means of using open traps
Special Weapons Squads: Special weapons, unlike heavy weapons, have a relatively poor range, making these units unfit for open traps. The only possible exception is special weapons squads equipped with grenade launchers, but even this will commonly require the squad to move forwards and put themselves at undue risk to complete their objective.
Hardened Veterans: Veterans have access to a heavy weapon, and are thus able to place open traps. This type of unit shares all the benefits and faults of the command squad, with a few exceptions. The first is that they are better trained through experience, and are thus more likely to hit with their weapon, increasing the effectiveness of an open trap. As well, veterans are able to infiltrate, and thus set up a far better firing lane after the enemy has revealed their deployment. The primary drawback, however, is that this unit can also carry a great number of special weapons, a potential which is wasted through the methods of movement and firing present in a closed trap.
Ratling Snipers: Bedecked completely with heavy weapons, this group is ideal for open traps. Not only do they have the proper weapons, but as well they gain a further benefit from the cover that they will invariably be placed in, and are even unroutable by enemy gunfire. Though their use epitomizes that of a unit engaged in open operations, one is left, unfortunately, to find a variety of uses for their sniper rifle.
Ogryns and Storm Troopers: As neither of these units can carry weapons of great range, they are both less than suited to open operations. As well, as their strength comes mostly from tactics used in closed traps, it is furthermore a waste of these units' potentials to be used in this way.
Techpriest: If equipped with gun servitors, this unit can make an excellent fire base for open traps. The only unfortunate part is their price, which makes them logistically unsound compared to, say, heavy weapons squads, who pack the same firepower at two thirds the price.
Infantry Squads: This units are, in general, a fairly poor way to create open traps. While they can take a heavy weapon, and while the number of guardsmen in a squad does increase their resilience to a degree, it does not change the fact that their price per gun is prohibitively expensive compared to the benefits. As well, in an open trap, 90% an infantry squad's weapons will be out of range, rendering a vast majority of the squad worthless in this type of operation.
Conscripts and Armored Fists: It should be noted that, for the purpose of this line of thinking, both conscripts and the infantry squads which ride in a chimera suffer from the same problems as the above description of infantry squads.
Chimeras: Chimeras are another excellent way to place heavy weapons onto the field. Able to take up to 4 (including a hunter killer missile) which can be upped to 5, if the infantry squad to which it is attached has one, the Chimera can lay down an absolutely formidable torrent of fire when used for the purpose of an open trap. Note that this is an exception to the rule for infantry squads taking heavy weapons, as, when combined with a chimera, the squad is able to concentrate and coordinate it's fire to much greater effectiveness with a chimera, than it could with another infantry squad. The chimera gains further effectiveness for it's ability to engage in closed traps (as discussed later)
Sentinels: Sentinels are a good way to engage in open traps. Their price per gun is very good, and it has a very wide array of heavy weapons that it can take. As well, the sentinel can be used very well for closed traps. The only configuration for a sentinel that should not be used is that of a heavy flamer, as this weapon does not have the range to be effective in this type of operation.
Hellhounds: Though equipped with a heavy bolter, the main weapon of this vehicle has a range that makes it less than desirable for engaging in open traps.
Rough Riders: As this unit cannot take special weapons, and it's primary advantage is movement, there is little use for this unit for an open trap.
Leman Russ Battle Tank: This vehicle is the king of open traps. Equipped with heavy bolters or lascannon, this tank has more than enough range to engage in open operations. As well, this tank has a good price to gun ratio, can be upgraded to include 6 heavy weapons (including hunter killer missile), and has the armor to let this vehicle survive being somewhat out in the open (after all, drawing line of sight on another often means that it can draw a line of sight to you). Add to this that a three heavy bolter variant is excellent for making closed traps, and you get a very good unit indeed!
Leman Russ Demolisher: This vehicle is similar to the standard Leman Russ, but is poorer at making open traps, due to the greatly decreased range of its main cannon. A demolisher does, however, have the same sponson options as a standard Leman Russ with a few upgrades, one of which (the plasma cannon), can make the Demolisher useful for closed traps. Given it's increased cost as well as it's greater potential for the use of closed traps, and this tank simply looks inferior to open operations when compared to the standard Leman Russ.
Basilisk: The Basilisk is also a good unit for the purpose of open traps. With a main cannon that has an even longer range than the battle cannon, and, in an emergency, a heavy bolter, this vehicle clearly has the range and firepower for the job. It is inferior to the Leman Russ, though, in that it can not carry sponson weapons, and its armor is so much weaker that it will be less able to withstand the full frontal firepower that tends to descend on vehicles. At two thirds the price, however, the basilisk remains an attractive alternative to the Leman Russ for open operations.
As mentioned above, the creation of a closed trap involves units that must move to be of full effectiveness. As units engaging in closed operations will likely have only one shot to complete their objective, they must have more firepower to compensate. Closed traps, however, do not require weapons to have the same long range as open traps, as the units are likely to already be at a very intimate range with their enemy. Note that closed operations come both in the form of close range firefights as well as close combat assaults.
Command Squad: Command squads are an excellent unit to use for the purpose of closed traps. The first way to use these squads is to take advantage of the ability to take an astounding 4 special weapons. Whether you want to surprise light infantry with a handful of flamers and an officer equipped with a storm bolter, or chaos marines or monstrous creatures with a sudden plasma gun barrage, or the complete annihilation of any vehicle foolish to close near your lines with a meltagun battery, there is always a role for a special weapons command squad. The best way to use these is to keep the unit itself out of line of sight, giving morale boosts, and combat instructions to the rest of the force and then, once the enemy has closed to a very close distance, charge forwards at the last moment and unleash a lethal volley. Note that this squad is also at an advantage for it's low cost.
Another way to equip a command squad for closed traps is for the purpose of close combat. In this way, the officer should be equipped with either a power weapon (if you don't care about effectiveness), or a power fist. In the case of the latter, it is prudent to equip the officer with an advisor, preferably a priest. In either of these cases, all attending retinue should be given close combat weapons. Though this setup is more costly, A senior officer with a powerfist, and a priest with an eviscerator along with support from a retinue is clearly a very powerful unit, able to deal with any enemy.
Heavy Weapons Squad: These squads are completely worthless for closed traps, as moving the unit requires the heavy weapons to spend time getting set up again, by which point, it will be too late.
Special weapons squad: Unlike heavy weapons squads, special weapons squads are much better at closed operations. The primary disadvantage to these squads, however, is their expense, as well as their inability to take more than three special weapons.
Hardened Veterans: This is another unit that is excellent for the ability to use closed traps. This unit can take 3 special weapons (4 if you give the sergeant a storm bolter or, to a lesser extent, plasma pistol), and is even able to put out the same amount of firepower equal to a command squad, as this unit is more accurate, and thus will score equivalent kills with fewer weapons. As well, this squad can grow up to over double that of the command squad, which allows for even more firepower and resilience. Most importantly, veterans have the ability to infiltrate, which allows them to set up closed traps halfway up the battlefield, making the space between your line and the enemy's even more treacherous.
Like a command squad, a veteran squad can also be kitted for close combat. In this case, a squad should be equipped with a power weapon or a storm bolter for the veteran sergeant and either flamers or grenade launchers for special weapons. The rest of the veterans should be equipped with shotguns. In this way, a veteran unit can unload a lethal blast of highly accurate shooting, followed by an assault where the veterans gain the advantage of a charge. Conversely, the veterans can be equipped with shotguns and meltaguns with the sergeant carrying a powerfist. In this case, the veteran squad will be able to deal a painful volley to marines, monstrous creatures or vehicles, and then follow it up with a charge with a powerfist. Once again, this unit also gains an advantage through infiltration.
Stormtroopers: This is another unit that is good for the purpose of closed operations. While they do not have the raw firepower of command squads or veterans, they have different equipment and abilities that allow them to be very effective in this role. The first, and most crucial advantage, is the stormtrooper's ability to deepstrike. Using this ability, a stormtrooper squad can initiate a closed trap anywhere on the board, without the possibility that they will be destroyed by the enemy before they can complete their mission. While deepstriking is inherently risky, it also allows for more guaranteed success, as well as being able to bring a fair amount of firepower to places that your army might otherwise be unable to effect.
There are a few other advantages to stormtroopers as well. One of them is that they are much more likely to survive after springing a closed trap than are the low in numbers command squad, or the more poorly armored veterans. Though the latter can alleviate their disadvantage by remaining in cover, sometimes this luxury can not be afforded to a unit engaging in closed operations. As well, it is infrequent that a deepstriking unit will have the accuracy to land in a suitable defensive position. Finally, stormtroopers have other equipment upgrades such as krak grenades which allow for a unit equipped to handle infantry to also handle vehicles, and targeters, which allow the unit to know if they are in range for a closed trap or not.
Ogryns: This unit is also acceptable for closed traps. Equipped with an assault weapon, and with great strength and durability, this unit can function much like veterans. The obvious disadvantage is that this unit cannot take special weapons, and is thus unable to be as effective in killing, but it's toughness makes up for this ability in close combat. Note that Ogryns must be hidden, as they are susceptible to death by high strength weapons.
Techpriests: If equipped with close combat servitors, this unit can make a powerful close combat unit. The only problem, however, is this unit's relative lack of survivability. It is, however, slightly cheaper than a properly equipped command squad and, assuming that it can survive, has the potential to do more damage.
Ratling Snipers: This unit is completely useless for closed traps in the same way that heavy weapons squads are. Worse, they lose their advantages of cover if they are forced to move from it.
Infantry Squads: Equipped, by default, with short range weapons, the initial state of an infantry squad makes it seem more suited to closed traps. As well, squads can then be equipped with a special weapon to serve this purpose. Unfortunately, the price to gun ratio in infantry squads is poor in comparison to the other great options available for this type of operation. In the end, the infantry squad is better doing closed traps with a special weapon as adversed to open traps with a heavy weapon, as at least the standard guardsman will be able to use his weapon.
One of the few advantages to an infantry squad using closed operations is that, with nearly double the number of men, it is more survivable than other, higher firepower squads, especially if they are kept in cover or other defensible position. As well, note that infantry squads can have assigned to them a veteran sergeant who can carry either a plasma pistol or a storm bolter (or regular bolter). This is seen by most commanders, however, as prohibitively expensive.
Conscripts: Conscripts have the same advantages and disadvantages as a standard infantry squad with a few exceptions. The foremost is that it is much more difficult to hide a large unit of conscripts for the purpose of keeping them safe before the closed operation. As well, as conscripts are poorer soldiers, there is even less killing power and a poorer cost to gun ratio (especially as it is more difficult to equip conscripts with special weapons, with which they are less accurate). Conscripts do, however have the ability to affect as a psychological weapon. While a group of 50 conscripts is unlikely to kill more than a few marines, the knowledge that your opponent will have to face down such an irreproachable torrent of fire may well keep them away from the unit.
Chimera: Like all vehicles, the chimera does a good job at setting closed traps, as it can preform this operation with heavy weapons. As well, if the infantry squad inside is equipped with a special weapon, it can add it's firepower to that of the chimera. The only problem with this is that there are few special weapons that perfectly compliment the heavy weapon options of a chimera, with the exception of a chimera outfitted with two heavy flamers, and the squad inside with a normal flamer. This setup, however, suffers from a tremendous difficulty in getting all weapons into a proper firing arc.
Sentinels: Sentinels are a decent choice for a closed operation. Not only can they take a heavy flamer, but as well, none but the hardiest of infantry can even have a chance at hurting the vehicle in close combat. Thus, while the sentinel itself may do little damage, it will effectively neutralize most units that it assaults. As well, this vehicle can shoot a heavy weapon and then assault, giving it a surprising second option to use against vehicles.
Hellhounds: This vehicle is much more useful for closed operations than that of open ones. In this case, the closed trap is sprung when the intended target is within range of the hellhound's main weapon, which it can move and then shoot. As well, this unit ignores the cover of those who face against it, which is likely to be in cover if it is a unit that is a part of an open operation.
Rough Riders: This is another unit that excels in the closed role. This unit can move very fast, which allows it to spring closed traps from much further away than most other guard units. As well, this speed allows this unit to ignore the cover or line of sight blocking terrain advantages by simply riding around them. While this unit can not take as many special weapons as other units, they do gain the ability to get closer, sooner, and set up traps up the field. While they are not as able to get into position as quickly as infiltrating or deepstriking, rough riders gain a further advantage in being able to quickly redeploy to other parts of the field to lend support. As well, this unit can take lances which provides a devastating attack on the charge.
Leman Russ Battle Tank: This vehicle is acceptable at preforming closed traps, being able to move and fire a full set of secondary weapons, or being able to move and still fire its main cannon. Use of a standard Leman Russ in this way, though, negates it's primary advantage: the range of it's main cannon.
Leman Russ Demolisher: This tank excels for the purpose of closed traps over the standard Leman Russ for several reasons. Firstly, it's main gun's disadvantage of a shorter range is negated by a closed operation. As well, the main cannon has a higher strength, and better armor penetrating abilities, making it able to do more damage in the brief time that it has to do it. As well, this vehicle is better armored making it more able to survive out in the open after a closed operation, and it is better able to defend against an enemy which then tries to instigate a closed trap against it.
Basilisk: Being poorly armored, and only equipped with weapons that rely on long range, the Basilisk is the poorest choice for use in closed traps. The only advantage that this vehicle has is price, but this is generally outshined by the greater usefulness of other vehicles.
The ability to bring a preponderance of units good for the execution of static operations is unique to the imperial guard. While other armies can duck in and out of line of site without recourse, the guard can simply hit enemy units without getting into line of sight in the first place. For the sake of simplicity, let us only consider the units which have the ability to take indirect fire options.
Command Squads: The command squad, when equipped with a mortar, is one of the cheaper options for taking the weapon. Given the massive potential for command squads in the closed operation role, this option should only be exercised if there is insufficient resources available to properly equip a command squad:
Heavy Weapons Squad: This unit is the best one to carry mortars. Not only are the the most cost effective way to deploy mortars, but as well, they fire in a barrage. This allows for greater accuracy as even if the ranging shot is off, the second and third mortars have the ability to scatter back onto infantry formations. As well, if the ranging shot hits, it can deliver a surprising amount of damage to light, open topped vehicles.
Infantry Squad: While infantry squads can take mortars, they suffer from the same faults as taking heavy weapons. The cost effectiveness is low, and a very large portion of one's army will be spent idle while the mortars do their job. That being said, it is one of a small list of units that can even take mortars in the first place.
Hardened Veterans and Conscripts: Both of these units suffer from the same problems as with heavy weapons. In the case of the former, it is a waste of good potential to give a mortar to a veteran squad. Likewise the problems of idleness are only exacerbated with the larger squads of conscripts. That being said, the mortar is the only squad whose accuracy is not impaired by the worse shooting skills of conscripts.
Basilisk: The basilisk is, obviously, the king of the static operation. Being able to do tremendous damage at incredible range for a relatively inexpensive cost, this vehicle is a must for the commander that wants to kill the enemy while not being seen. The only drawback to the basilisk is that, once the enemy enters its blind spot, the vehicle must rely on other operations to continue to be effective, removing a great deal of your ability to conduct static traps.
It should be noted that some doctrines can be used to enhance the abilities of certain units to perform their assigned operation. The following is a brief summary of these doctrines.
Light Infantry: Light infantry can greatly augment a unit's ability to conduct closed traps. Not only does it make it so that a commander can set up closed traps far upfield, but as well it makes it easier to spring closed traps by causing terrain to be less of a hinderance. This is especially important for units that are attempting to make it into assault.
As well, light infantry is useful (if less so) for open traps as it allows units to set up their fire lanes after the enemy has deployed their units. Thus, the right weapons can be placed where they will do the most damage to an enemy's units or plans.
Drop Troops: This as well can be very useful for the purpose of creating closed traps. The main drawback to this is that few units are reliable enough to survive after the trap is sprung, especially without the support of friendly units, or the reliable benefit of cover.
Mechanized: This doctrine is helpful for open traps as it greatly increases the number of heavy weapons that you can bring to the battle. As well, it can be useful (if less so) for the creation of closed traps, as the vehicle can still move and shoot (although this wastes the heavy weapon's potential).
Cameloline: This doctrine is useful for open operations as it helps a unit continue to serve it's purpose, though being in line of sight of the enemy. This is much less useful, though, for closed traps, as such units should be hiding behind cover rather than in it. Note that many commanders find this equipment prohibitively expensive when compared to simply bringing another unit to the field.
Warrior Weapons: This doctrine, when used properly can greatly increase the effectiveness of a unit attempting to use closed traps. In this case, a unit so equipped would pounce forward, fire assault weapons, and then charge, gaining an extra attack over that of rapid firing a lasgun. This is especially well complimented by a priest attached to the unit.
Using the ideas discussed above, an imperial commander can better understand which units will get the most out of the role that the commander desires. Always remember, though, that a unit can be used for more than one role, and a good commander will be able to switch in the field. It is, however, always best to have a unit that it best for any given role to fulfill that role on the field.