Master of the Signal
The Master of the Signal was a type of Consul in the Legiones Astartes during the Great Crusade and Horus Heresy. As the name implies, they were incredibly specialised marines in charge of communications.
Overview
A Master of Signal was commonly attached to the forward elements of a Space Marine assault, providing communications support across the wider warzone. They were capable of calling down a pinpoint bombardment from either orbiting fleet assets or static artillery positions nearby. To help them do their jobs right, they were equipped with top-of-the-line gear, including a Cognis Signum that allowed them to deliver accurate coordinates to whoever was about to ruin the other side's day with a bombardment. They also got a nuncio-vox built into their helmet, hence the large receiver antennas and overbuilt helmet. As they were Consul rank, they wore Mark IV armour. Unfortunately, one downside is that, since he is primarily a support guy, he lacks any real weapons for self defence.
Crunch
Horus Heresy 1.0
The Legiones Astartes were organised as a large-scale ground-taking force the same way that Guardsmen are organised in 40K, and that means dedicated comm specialists for manoeuvring and coordinating vast amounts of firepower. Step in these bois, who don't disappoint when it comes to beefing up a gunline. Each has a once-per-game S8 AP3 D3 Large Blast Orbital bombardment and comes equipped with a Cognis Signum that, among other neat benefits, grants +1 BS to a single friendly unit within 6" if he doesn't shoot that turn (which he won't, as he can't even take a bolter). They also carry a Nuncio-vox, enabling Barrage weapons to use his line of sight, allowing for much more accurate artillery fire and no-scatter deep strikes. If you were planning to deep strike all over the enemy's face and cover him in pie-plates the Orbital Assault RoW works best. Enjoy your accurate Rapier Quad Mortar barrages. This fella is no good himself in close-quarter combat, nor does he boost melee efficacy, so you'll want him away from brawls and hidden among shooty doods like Seeker, Heavy Support and Tactical Support squads, Rapier batteries and so on. But don't forget - the Nuncio Vox can be used to make accurate deep strikes, which in a pinch can be used to call in some Assault Squad reinforcements to protect the gunline should enemies encroach.
- In return for all his fancy base kit, the Signals man has very limited wargear options: He can't take Terminator armour or any kind of bike. In fact, the only things he can take are power weapons (but no power fists), a Volkite charger, pistols, a charnabal sabre or a heavy chainsword. But he buffs your army with just his mere presence, so you could take him naked (or with Artificer & Refractor protection) and even at just that he's one of the most useful Consuls.
- With the new FAQ the Master of Signals has become somewhat horrendous in the right circumstances. Being able to fire his bombardment when he has moved, from a fire point or has disembarked at a DIFFERENT TARGET to any attached unit is frankly jaw-dropping. This coupled with his nuncio-vox makes him a fantastic support character for an Orbital Assault list (Bring him down turn 1 with a squad of guys with scary guns, fire the bombardment then intercept something next turn and give you 6" no scatter for another unit for the low price of around 100pts is amazing). Rites of War such as The Black Reaving and the Logos Lectora suddenly got a bit better with the mandatory inclusion of this little guy.
Horus Heresy 2.0
Has more wargear than he can keep track of and all of it is useful. His Strategic Comms special rule allows any friendly unit on the table to use his leadership for Morale or Pinning checks (but only once per turn), and as long as he isn't in Reserves then you may re-roll your Reserve rolls. He comes with a Nuncio-vox to re-roll Deep-Striking scatters; an Augury Scanner, preventing Infiltrators from deploying nearby and granting free Interceptor reactions; a Cognis-Signum, granting Night Vision and +1 BS to his squad; and a Vox Disruptor Array, making all Deep Strike, Drop Assault or Subterranean Assault rolls become disordered on a 1-3 at no cost, which he can switch on and off at will each turn. He can't exchange his Chainsword for anything that isn't a Power/Charnabal weapon. He also can't take a Combi-Bolter or regular Bolter, but it seems GW forgot they'd added Shotguns and Nemesis Bolters to the list because he can still take those (or a Volkite Charger). No shields, bike, or Jetbike either, but he may take a jump pack if you're a masochist who wanted him to make his own Deep Strike disordered.