While the 10th edition Astra Militarum codex introduced many changes, a quickly overlooked one was the retirement of the basic, unbranded, Infantry Squad and its sister units. While seeing models dropped from their range has been a common thing in 10th, this was a unit that had been in constant use since 2nd edition, and a battleline choice to boot. We still have infantry, mind you, such as those associated with the three big name regiments, but this presents something a bit odd. Previously, Cadians, Catachans, and Krieg were reactions to or variations on the basic Infantry Squad, and now that no longer exists. An entire play style is now gone. Does this mean much for the Guard? GW has been working up to this for a while, after all. Perhaps not a lot, but let me explore the topic.
To start with the basic template, Guard battleline infantry are a Toughness 3, 5+ Save, horde unit, usually favouring quality over quantity. These have numerous peer units, think Chaos Cultists or Tyranid Termagants, although they are often outperformed by the likes of Orks and Alderi. Guard infantry are usually regarded as amongst the weakest units in the game, especially in the realm of melee. They don't shoot, stab, or absorb bullets very well. These limitations are however offset by the Order system, which allows for various useful buffs. Historically, a major strength of these units was the availability and variety of heavy weapons, but with the removal of the old Infantry Squad that's no longer a thing. You can't easily secrete lascannons and mortars amongst the rank and file to increase their effective threat. This means the battleline infantry now operate mainly in the 12-24 bracket, mostly using plasma and melta weaponry to offset the famously low-end lasgun. A consequence of this is that your infantry is somewhat more likely to end up in a melee than before, which likely won't suit them. Furthermore, the Astra Militarum has actual variety in its detachments now, and in several them battleline units are actively selected against. Combined Arms, Recon Element and Siege Regiment can certainly make use of them, but in the others there's a preference for the more elite infantry. Part of that is the matter of transports, but I'm not getting too deeply into that today, its a lengthy topic. Battleline guard can get good use of Chimeras and such, but other units can use them better. What do these models excel at then? Well, objective control and screening. Guard infantry tend to offer a lot of OC for their price, and can cover a lot space on the table to frustrate enemy movements. These units can be surprisingly quick if properly managed, perform mission actions as well as anyone, and can be quite disposable. These are not your primary damage dealers, these are the unglamorous workmen or women of your force that score you points and contest the mid board. Where Cadians, Catachans and Krieg differ is how they approach those sort of tasks.
Cadian Shock Troops
Any discussion of these starts with a Cadia Stands meme, and then a discussion of the "Sticky Objectives" rule they have. This means that they do not have to physically be on an objective to hold it, and slows enemy attempts to flip such an objective. This is an undeniably useful thing to have in your toolbox, although it presumes that the unit will be both on foot and in motion. That's not a given in the wider context of this army, and it may be something you don't need a load of. I keep trying to use that ability, and it doesn't seem matter much given my play style. However, Cadians have the most extensive officer pool, including a pretty good Command Squad that now grants Cover when on an objective. The changes to medpacks in general meanwhile also make large squads more practical, and thus holding objectives. Shock Troops look like the generalist option at first, and I suppose they are by default, but I invite you to consider their name. There is a certain presumption of mobility there, especially in the context of the Castellan's fallback & shoot ability. Cadians are the ones most interested in objective play, with a secondary (actual/better?) function in maintaining the chain of command. However the other options here are more capable of either A) getting to an objective or B) holding it, if not both at the same time.
Catachan Jungle Fighters
Beloved of the tournament scene, the Jungle Fighters have a somewhat deceptive datasheet, and a good example of how raw damage output isn't the only metric. Due to them having a very old (awful) kit, this battleline unit has no real equipment options other than vox units & flamers, and a melee rule I'd describe as "well, okay then." They can beat up or burn alive similar costed units, but you feel the absence of melta and such. What makes them useful is the Scout rule, which gets them where they need to be that much faster. A Scout move, a Move! Move! Move! order, followed an by Advance averages out to about 18.5 inches of mobility on turn one. That's easily on an objective, and Catachans have a well-known role as Chimera passengers as a side effect of that. Where Catachans really benefit from the new codex though is the creation of their new Command Squad, which keeps the Scout rule while addressing the equipment issue adequately with similar options to their Cadian counterparts. And the Assault rule for all ranged weapons. This presents something of a dilemma with respects to unit sizes and investment, as there's a good case for disposable units of ten only, but you do have options that make up for the loss of named characters like Ironhand Straken. One factor to keep in however is the Scout rule is much more frequent in this codex, through various means, so you may find other options more appealing.
Death Korps of Kreig
Kriegers were told that the basic function of a guardsman was to die horribly, and responded by saying: "Yes please, more of that.". This unit embraces attrition like few others, as minor casualties make them more accurate, while a badly mauled unit will be punching up quite significantly with its surviving models. Also, while model regeneration is much more common in this ruleset due to the new medpack conventions, Krieg has that at the individual squad level and with greater proficiency. There's a strong/pull dynamic at play with this unit as a result, and of all the battleline options, the Death Korps make the strongest case for being actual damage dealers, having that buff ,and the small but important addition of power weapons and plasma pistols to their sarge equivalents. The unit does benefit from Orders, effects of those and Grim Demeanour stacking, but doesn't necessarily need them to work. The context they operate in has however changed around them, the loss of the Death Korps Marshal being keenly felt for example, and their datasheet is an obtuse mess. EDIT: Now fixed. The new Krieg Command meanwhile is inflexible but reinforces the attrition theme by largely negating battle shock and offering some redundancies. Krieg battleline are the spiteful ones, and work best in bigger squads doing a collective Necron impersonation while overheating their plasma guns. Squads of ten, possibly operating from a transport, are a touch less compelling to me. You do get more stuff, but it becomes more likely that the unit will be wiped before Grim Demeanour kicks in. I'm quite fond of Kreig at present, but I do feel their limitations.
Conclusion
I don't consider myself any authority on Astra Militarum tactics. Rather, I expect the issues discussed above to be worked through and analysed by better players. I do however mourn the loss of the classical guard gunline, and this document is me attempting to process this. So, for a practical conclusion? Choose the one you like the look of best, but maintain a squad of each other regiment just in case either the meta changes or your mind does. They are all pretty similar, but they do meaningfully different things once you get used to them. It may indeed be that having a mix of these is the way to go, but don't quote me.
