These are mean killers, they are our 2+ save 2W tank eating monsters, almost as tough to kill as paladins and thunderwolves, though a much closer analogy would probably be Obliterators. Armed with a twin-linked railgun, also known as that tau gun with maxed out stats, and a Smart Missile System by default. Unfortunately, these suits are NOT jetpacks, but really the trade-off is worth it. They can, on most boards, target any unit with their 72" range, which is also nice.
These guys are NEED shield drones, they are almost mandatory. The sooner you accept that, the sooner we can move on to the next point. Otherwise, you'll straight up lose a broadside to a stray lascannon shot, or be plasma'd to death, or whatever. Generally, you'll want to hard-wire the drone controller on a team leader, so that your suits can benefit from precision shooting (as team leader are characters) and so the team leader can benefit from their exceedingly useful support systems.
The available support options are:
-Blacksun Filter. Exceedingly cheap at a measly 3 points, grants your broadsides nightfighting. Very useful, especially with how common Nightfighting now is, though it rather pales in comparison to the other options. If you are taking this, it should either be a points-cost consideration, a budget option if you will, or as a hard-wired support option on the team leader, as he now grants it to the whole unit.
-Multi-Tracker. Fairly cheap at five points, and may help with overwatch. Letting you shoot both your primary AND secondary may sound fairly good, but in most cases, anything your Smart Missile System will do well against, your railguns won't, and vice versa. Really, there are very few times you should ever use the SMS, it is really only a last resort "I'm about to be charged by guardsmen" kind of weapon. May just be worth it if you take Plasma Rifles.
-Advanced Stabilization System. Awesome piece of wargear for broadsides, as it was designed for them. It gives them slow and purposeful. It used to be pretty good, back in 5th edition. Now it is great. They can move the full 6" and fire their heavy weapons at normal BS, useful for backing away from an assault for an extra turn of shooting, or for maneuvering for some shots at side armour. The only downsides (minor) are that you cannot run, and you cannot perform overwatch.
-Targeting Array. +1BS, same as on a crisis suit. This makes broadsides just that little bit more reliable, to make them a true nightmare for their enemies. Quite the opposite of the A.S.S, which focuses on adding mobility, this makes them even more deadly when they stand still, and gives them a nearly 90% chance to hit!
-Shield Generator. I, generally, would not take this. Doesn't make them any shootier, as all the other option do, and is 2-6 times more expensive, depending on which other wargear you compare it to. The invulnerable saves really should be on the shield drones, as most weapon that can pierce their armour will instantly kill them, and you do not want to pay 20pts for a 50% chance to save it.
-Drone Controller. This should ALWAYS be hard-wired unless you are well and truly strapped for points, which you should be, since broadsides should usually be one of the first things you add to your army roster. Generally, two shield drones is a great option to accompany this wargear. Gun drones are okay, but kind of out of place, and really more useful is you just want some ablative wounds and don't care about SD having 2+/4++ T4 (...?). Marker drones are too expensive.
The other pieces are irrelevant, or defunct (target lock).
Now, the other option they have is to take Twin-Linked Plasma rifles as their secondary weapons for 10 points. Now, this one is kind of iffy. Firing this means you're not firing your railguns. It also means the enemy is within 24" (you DON'T want them to be within 24"). Firing this AND your railguns means that you have a multi-tracker, and not one of the more awesome upgrades (like the A.S.S or the TA). So you see the problem. Logically, you should never fire them. So why would you buy them? Also, in some cases the SMS is actually BETTER, not needing line of sight, ignoring night fighting and having more dakka.
The one time I can see it being okay is with a Multi-tracker, against terminators (terminators who aren't thunderwolves or paladins, or have storm shields). If your opponent is playing deathwing with shooty terminators, or just has normal terminators for whatever other reason, then you have to realize: a plasma rifle shot has the same effect against a terminator as a railgun, and this way you can get three twin-linked armour piercing wounding on 2's shots off a turn. Still not worth it, but a consideration if you are in that particular situation.
Now, on to tactics. In 5th edition, they were really quite straight forward: either set them up in the backfield and shoot anything with an Armour Value, or use them as bait for Patient Hunter (kauyon) strategies. With the coming of 6th, there are decidedly more options, thanks to allies.
There are three worthy of note, two of which are related to the Space Marine Librarian.
-You can give the librarian Gate of Infinity, and teleport the broadsides out of harm's way whenever anything threatening looks at them wrong, or just to get side/rear armour on vehicles.
-A librarian with Force Dome gives them a 5+ invulnerable save. With cover now granting a 5+, that means there is no direct benefit to staying in cover (other than sight lines, enemies charging through difficult terrain etc.). Logically, this means you are free to move your broadsides around, ignore the confines of cover, simply moving around to get the best angles of attack. Note that broadsides working with either librarian tactic are best off with A.S.S.
-Necrons can add nightfighting. Broadsides can ignore nightfighting with the right wargear.. Nothing will be able to shoot them beyond 36", and they get bonuses to cover saves short of that (potentially getting a 2+ cover save in ruins!) while they can plug away at 72" and not grant any cover bonuses. Unfortunately, necrons otherwise have poor synergy with tau, but oh well.
Now finally, let's look at the pros and cons of broadsides.
PROS:
-Are armed with THE best tank eating gun in the game, twin-linked.
-2+ armour save, with 2W.
-Can be equipped for a variety of situations with highly customizable load-outs.
-Reasonably priced (rare outside of Imperial armies)
-High perceived threat, useful as a lure.
CONS:
-No invulnerable save.
-Has trouble with infantry.
-Obvious target.
Conclusion: Best source of railguns available, and you love railguns. Therefore you love broadsides. More or less mandatory for a competitive list.
