Note: This tactica article handles Bike Squadrons in Codex: Space Marines. Bike Squadrons in Codex: Dark Angels and Blood Angels as well as Blood Claw Bikers in Codex: Space Wolves will have similar, but in some aspects, different builds and tactics.

The Bike Squadron is of the fastest units available in the Space Marine codex. Only the different kinds of Bikers and Land Speeders can move up to 24" per turn, which of course has several tactical advantages. But we'll first have a look at the different builds that I see a lot.

Different builds:

Bike Squadron
Veteran Sergeant + 3 Bikers
Power Fist, Bolt Pistol, 2 Meltaguns
Attached Attack Bike w. Multi-Melta

Simple tank hunting squad that are able to move very quickly and thereby easily get into melta range by turn two.

Bike Squadron
Veteran Sergeant + 3 Bikers
Power Weapon, Bolt Pistol, 2 Flamers
Attached Attack Bike w. Heavy Bolter

This squad is generally a very mobile gun platform and can hunt light infantry. The Power Weapon can of course be swapped for a Power Fist if desired. I'd say that this squad is best used in an army that has taken Be Swift as the Wind as a trait advantage, and then taken as Elites. This will give them Furious Charge, something that the Veteran will benefit from a lot.

Those are the two most common units I've seen so far. Some people leave out the Attack Bike, some adds a fifth regular Biker and so on. I would like to argue that you could (and mostly should) swap two Bikers for an Attack Bike. The Attack Bike with a Heavy Bolter is cheaper than two Bikers, and the Mutli-Melta version is one point more expensive than the two regular Bikers. The squad's efficiency is increased in some aspects, mainly in the shooting phase of course – since the heavy weapons are bike mounted and thereby can move and fire. You'll still keep one Bolter as well, plus you can take one wound without decreasing the efficiency at all in shooting. The only downside is that you'll lose a single attack in the assault phase. Good deal, don't you think?

There are other options as well for Bikers, to take Melta-bombs for example. These are quite cheap, since the squadron is small. They can be good for at least the infantry-hunting squadron if you stick with the Power Weapon. That way, they can blow up tanks while still retaining their edge on light infantry. If your list contains a Chaplain on a Bike, go ahead and attach him to the squad as well.

I do not recommend that you give your bikers Plasma Guns. First of all, Plasma Guns can overheat, and since a single biker is so expensive, it'll hurt. Secondly, Plasma Guns are rapid fire weapons, and they are not fitted to the bikes, so you can't shoot Plasma Guns and charge afterwards.

Important rules when using Bike Squadrons:
All models in the Space Marine codex that are mounted on bikes have the turbo-boost special rule as detailed in the Warhammer 40,000 rulebook. This is a great addition since the third edition in my opinion. It greatly increases the survivability of the squadrons, and they can easily be in your opponent's lines by turn two due to this. Use the rule with caution though, as the Invulnerable Save they claim actually replaces their regular Armour Save. Thus, some weapons – like Psycannons or Incinerators – will deny them their save all together.

Furthermore, you might have noticed that I've listed Bolt Pistols for the Veteran Sergeants in both squads. Usually, a Sergeant is able to replace his Bolter with a Bolt Pistol and Close Combat Weapon for free, but in this case, he's not. He has to buy the Bolt Pistol from the armoury, and don't forget it, or else your Sarge's effectiveness will be reduced.

Now, in the third edition of Warhammer and the third edition of Codex: Space Marines, Bikers weren't able to wield two weapons and ride a Bike at the same time (with the exception for White Scars), because a Biker has to have one hand on the handle bars at all times. Very logical. In the current fourth edition of Warhammer and Codex: Space Marines, there isn't a single line written about how you have to keep one hand on the handle bars at all times. It does so in Codex: Chaos Space Marines, but not in the loyalist book, so all bike mounted models in your Space Marine army can have weapons in both hands.

Remember also that a squad is as big as its number of wounds, not models. So the squadrons listed above are all even-numbered, which is better for Victory Point-purposes.

Tactics:

Finally, we get to the good stuff. Bike Squadrons are actually quite fragile, despite the good armour save and higher toughness than regular Marines. This has of course to do with their strictly limited squad size. When you use bikers, you should adhere to some fundamental tactics:
1. Never mix the weaponry in your squadron. It is better to do one thing good than to do two things half-assed. Bike Squadrons needs a clearly defined role to be effective.
2. Use terrain as much as possible. Move the squadron up behind terrain as much as possible. Stay out of area terrain though, because a bad roll on the dangerous terrain test can ruin the entire squadron.

Then you'll just have to do what is best suited for the bike squadron. If you play with the infantry hunting squad, go after Pathfinders in ruins, Gaunts, Ork Boyz and similar things either too light to withstand a couple of Flamers and Bolters or units stuck in terrain. If you play with the tank hunting squad, go after those Leman Russes, Predators and other heavy tanks or heavy infantry.

Generally, Bikes are at their best when working around the flanks of the enemy, and not in the direct line of fire. As the squadrons are so small, every failed armour save will hurt, and they are also vulnerable to the torrent of fire rule.

You should also refrain from just charging into assault as soon as possible. Again, the small squadrons are the weakness, despite the higher toughness and good save.

Bike Squadrons are best used as harassing units when going after infantry. Since they are very fast, they are able to stay out of range of assault from a lot of enemies, and still fire their bolters at the long range mode – since they are fitted to the bikes. So any target you've picked out for your Bikers will probably have to be softened up before the Bikers move up, Flame them and then charge in to finish them off.

There is also another advantage when it comes to speed: you can capture objectives late in the game. A last turbo-boost into an objective can win you the game – either by you gaining more Victory Points, or denying your opponent his.

Conclusions:

Bike Squadrons are one of the speedier units in Codex: Space Marines. Some armies like those who utilize Be Swift as the Wind and Dark Angels 2nd Company – “The Ravenwing" – employ little else but Bikes and those armies can even compete against Eldar and Dark Eldar in terms of speed.

They are also one of the most fragile units, and thereby needs a lot of caution to use correctly. As such, they will need a lot of practice and work before they are really effective.

Still, if you can make them work – either in a list with a whole bunch of them – or just as a support unit in another list, I'll guarantee that they won't let you down.