Sky Hunter Squad
Sky Hunters were specialized fast-attack Space Marine units used by the Legiones Astartes during the Great Crusade and Horus Heresy. They were the next step up from the Legion Outrider Squad.
Overview
Mounted on Imperial Jetbikes, Sky Hunters were feared reconnaissance and first-strike units, boasting considerable firepower on their mounts in addition to their superb speed and manoeuvring capabilities. The jetbike patterns in service with the Sky Hunters, including the Scimitar, Bullock, and Estoc patterns, were typically modifications of designs which considerably predated the Imperium. Though they were powerful and highly sought-after force multipliers, they were also maintenance-intensive and required rare materials and technology to be built. Thus, the demand for jetbikes always outstripped supply and only a few of the Legiones Astartes could field them in great numbers, most notably the speed demons of the V Legion. In the aftermath of the Horus Heresy, the Imperium's infrastructure and knowledge base was so fragmented that the materials and technology needed to build jetbikes either became too precious to use or were gradually lost over the centuries, along with the knowledge of how to maintain them. This spelled the end of the Sky Hunters.
Sky Hunters typically operated in squadrons of three, each led by a sergeant. Their jetbikes, mainly Scimitar and Bullock pattern, sported a mixture of Heavy Bolters, Multi-Meltas, Volkite Culverins, and Plasma Cannons.
Crunch
Horus Heresy 1.0
The famed Dickbikes. 3-10 strong, 1 in 3 can replace their Dickbike Jetbike's mounted heavy bolter with a multi-melta, volkite cannon or plasma cannon. They can buy melta bombs and they can Deep Strike, but only the sergeant can buy a power weapon (while he's technically an upgrade, he's practically an auto-include, improving your melee punch and giving an extra point of Ld to save your fairly expensive squad). Very high mobility coupled with T5 and a 2+ save with Heavy weapons makes for a very powerful combination. Aim them at the enemy's vagina/anus and let them fly.
Horus Heresy 2.0
A combination of the Sky Hunters and Sky Slayers from last edition, 2.0 Sky Hunters are now heavy weapon carriers in the Fast Attack slot, with a Move characteristic of 16" and 2 wounds. Any member of the 3-10 man squadron can replace their Heavy Bolter with a Volkite Culverin, Multi-melta or Plasma Cannon. The squad has both Deep Strike and Relentless, giving them far more mobility than an infantry Heavy Support Squad... but with a much higher price. Interestingly, they can also take a Nuncio-Vox and a Vexilla. As bikers, they have both Hit & Run and Hammer of Wrath, but unlike Outriders they may not take Power Weapons. They do come with Pistol + Chainswords stock, though. Jetbikes are now T4 2W with a 3+ save rather than T5 1W 2+. This rounds out to make them easier to kill with most small arms, as having 2 wounds is balanced out by failing twice as many armour saves against AP4-6, on top of being easier to wound. You also no longer get saves against AP3 weapons and things like Krak Missiles will ID you, so 2W doesn't matter. However, the Scimitar Jetbike, like the Spatha bikes, can get Shrouded (5+) from Running, so they effectively can still Jink.