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AFAIK yes, even todays armored divisions have organic infantry troops in the organization chart... though light infantry regiment like tanith can have little to no armored vehicles and drop troops regiment is limited to light vehicles like sentinels that can be grav-chuted

Considering the Catachans have a Sentinel pattern named after them...

What about anti-tank weapons? Grenadiers woefully lack in that department. If you want elite, go for deep striking Elysians, but with both meltas and missile launchers.

NO! Grenadiers are storm troopers as troops choices minus infiltration and deep-strike options. Vostroyans don't use grenadiers, but they do have carapace armour.

Well, I mean, I'd still have heavy weapons teams and special weapons teams, but I'd likely only take a single platoon, if that. It's more theme based that anything else. I mean, that's a reeallly vague concept, but I was just wondering if anyone's played it before, or seen it done before, or even if you hadn't, and had any suggestions.

They're just the same as any Imperial Guardsmen, excpet their doctinres are (I think):

Carapace Armour
Heavy Weapon Platoons
Iron Discipline
Special Weapon Squads
Hardened Fighters

It's something like that. I don't think they have any special particular rules.

Okay, rather than pay attention in Physics today, I started out making an army list for my theoretical army list, which I won't end up starting untill probably late spring or summer, if at all. I'm going really heavy for theme here, rather than actually making an effective force.

Doctrines:
Storm Troopers
Carapace Armour
Cameleoline
Sharpshooters
Special Weapons Squads

Command Squad: 180
Colonel (HSO) Power Fist, Plasma Pistol, Surveyor
4 Veterans, 4 Bolters, Medic, Vox-Caster
Carapace, Cameleonline, Sharpshooters
Fire Support Squad: 120
Heavy Bolters, Carapace, Cameleoline, Sharpshooters
Anti Tank Support Squad: 135
Missile Launchers, Carapace, Cameleoline, Sharpshooters
Special Weapons Squad: 105
3 Sniper Rifles, Carapace, Cameleoline, Sharpshooters
Special Weapons Squad: 120
3 Melta Rifles, Carapace, Cameleoline, Sharpshooters

Storm Troopers: 141
Veteran Sergeant, Infiltrate, 2 Plasma Rifles, Vox-Caster

Storm Troopers: 141
Veteran Sergeant, Infiltrate, 2 Plasma Rifles, Vox-Caster

Grenadiers: 133
Veteran Sergeant, 2 Plasma Rifles, Vox-Caster, Surveyor

Platoon Command Squad: 160
Lieutenant (SO) 2 Plasma Pistols, Surveyor
4 Veterans, 4 Bolters, Medic, Vox Caster
Carapace, Cameleoline, Sharpshooters
Infantry Squad: 122
Veteran Sergeant, Bolter, Plasma Rifle, Vox-Caster
Carapace, Cameleoline, Sharpshooters
Infantry Squad: 122
Veteran Sergeant, Bolter, Plasma Rifle, Vox-Caster
Carapace, Cameleoline, Sharpshooters

Well, that's most (if not all) of the Infantry part of it. I'm going to work in some Sentinels, and I'm thinking about what kinds of armour to use, if any. The only thing I know I want for it is the Macharius Vulcan Heavy Tank.

I'm going to be using Urban Mammoth's Viridians for my models as well. Thus, my normal infantry will look roughly like this:
http://www.urbanmammoth.co.uk/acatalog/13101.jpg
My Snipers like this:
http://www.urbanmammoth.co.uk/acatalog/13103.jpg
My Heavy Bolters like this:
http://www.urbanmammoth.co.uk/acatalog/13114.jpg
And my Missile Launchers like this:
http://www.urbanmammoth.co.uk/acatalog/13128.jpg

There are some other units I could display, but none painted.