Do the various Heavy Weapons Training talents cover really big stuff? Some examples:

-155MM Artillery

-210MM Howitzer

-Katyusha rocket arrays

-Surface-to-air missile launchers

The above assumes that the weapons in question are standalone and otherwise not fired through a vehicle's fire-control system. If it was, then I daresay an appropriate Piloting skill would be more appropriate . . . or would it?

If Rogue Trader is to be believed, if it's a weapon bigger than you can carry in your hands, you don't need a Talent to use it. It's dumb, but it prevents a buy-in cost for those that want to have vehicle combat. And it's still dumb...

I can imagine they did that for vehicle mounted weapons for the reasons you said but there should be a Ordenance Weapon training set for artillery. Which should cover indirect fire too, although it's never been mentioned in the rules. But then I don't think they ever mentioned firing a earthshaker cannon in the rules but I've not got rogue trader.

I'd say they're included in the Heavy Weapon talents, with most of the stuff you fire balistically falling under Heavy Weapon (Launcher).
Other than that, it's still BS for firing weapons - Pilot is strictly for moving craft in directions you want them to move in.

If Rogue Trader is to be believed, if it's a weapon bigger than you can carry in your hands, you don't need a Talent to use it. It's dumb, but it prevents a buy-in cost for those that want to have vehicle combat. And it's still dumb...

If Rogue Trader is to be believed, Macrobatteries (that's those things just a little bit larger than titan weapons...) don't need a talent for characters that are supposed to have been serving as officers of a spaceship. Rogue Trader rules are supposed to be used for Rogue Trader characters - if you choose to use them anywhere else, you just might have to modify them. After all, RT characters don't have the talent "Walk upright" either although this may present great difficulties to certain Xeno species.

Suggested skill: Artillery Aiming (Imperial) (int) .
Use Artillery Aiming to calculate elevation, direction, burst altitude and any other neccessary settings needed for effective firing of artillery. A You can take into account a multitude of factors, such as barrel length, weight of the projectile, propellant charge, wind drift, gravity, atmospheric density, cogitator assisted targeting, etc. You do also have the practical knowledge of how to effect these settings, as well as a cursory knowledge of most of the measurements for common imperial artillery. In theory you can even load the pieces by yourself, but usually there is a crew to handle that. Any artillery shooting in a situation that you do not have good data on will suffer a penalty of up to -60%, less data gives a worse penalty. This penalty will decrease by 10% for each round that you fire and manage to observe the effect of your fire, thus learning to compensate for local phenomena. Another person with the Artillery Aiming skill can act as your spotter, as long as you have means of communication. For the purpose of checking this skill anything your spotter observes can be considered observed by you and to hit modifiers for range can be calculated from the spotters position. Maximum range is still calculated from the artillery piece.

A skillcheck is an extended action taking 12-(IB) rounds, a minimum of one full action. Making an adjustment of aim is a full action. If the factors are stable (stationary target, stable winds and atmospheric composition, etc) you can keep your original roll and just add a bonus of +10% for each round spent making adjustments.

A success on the skill check means your intended target is within the area of effect. Every two degrees of success means one aditional hit, as your central blast is closer to the intended target. Up to a maximum number of hits dependant upon the ammunition. Anti-tank shells do not benefit from extra degrees of success, and suffers from a huge negative modifier to hit. This can be compensated by active targeting systems and/or by firing them at large targets, such as tanks and bunkers. Good maps, a spotter, a good rangefinder, precise and updated info on factors such as wind, a decent cogitator or an astartes type battle-information-grid are some of the things that give bonuses. This skill is also useable for shooting some Heavy (launcher) weapons indirectly, if it is mounted with the ability to set elevation etc.

A moritat assassin will have to pass a WP check for any use of this skill, even if you mount a bayonet on the barrel of the earthshaker cannon or on the projectile itself. A metallican gunslinger may not learn this skill at all, unless you craft a sufficiently epic low hanging holster to keep the artillery piece in. ;-)

There are probably xenos versions of this skill, such as Artillery Aiming (Ork). These are very limited in their availability to the imperial population.

New item: Imperial artillerymans field manual
Cost: 200 thrones, Rare, on the black market. 10 trones and Common, from Adeptus Munitorium or similar.
This is a field manual that contains specifications on most versions of imperial artillery pieces and their ammunition. It also contains crossreference tables to calculate elevation, compensation for wind drift and similar common battlefield maneuvers. A skilled artilleryman can use this book to check up and calculate firing settings almost as fast as a cogitator. Tables are provided for most environmental conditions that can be encountered within imperial space. Sometimes an expanded version is issued for a specific campaign or location that will suffer from extreme battlefield conditions, such as fractured inertia fields, very local gravity wells (vlgw's) or projectile reflective warprifts. These are commonly noted as IAFM-[campaign or locations name] edition and are much sought after by collectors, since most manuals are burned by inquisitors or commissars after the campaign. An IAFM halves the time required to perform an Artillery Aiming (Imperial) skill check to calculate settings for a piece of artillery, as long as current battelfield conditions are covered by the manual. Half time needed after subtracting the users IB and round up. So an artilleryman with an IB of 3 and using an IAFM would need an extended action taking five full rounds. (12-3=9, 9/2= 4,5 rounded to 5)

New item: Artillerymans measuring tools
Cost: 500 thrones, Rare, on the black market. 100 trones and Common, from Adeptus Munitorium or similar.
This is a set of finely calibrated tools that measure wind, gravity, elevation, distances etc in order to assist an artillery aimer in making correct settings. These tools give a bonus of +10% to any Artillery Aiming checks made. These tools work even better if several members of the artillery team, spotters included, have their own set of the Artillerymans measuring tools and are placed apart so that they can triangulate and compare readings effectively. In that case the bonus can be increased by +10% for each full turn taken to compare readings. The Artillerymans measuring tools can at most give a bonus of +30%.

New action: "Fire on my coordinates!"
This is a full round action enabling a person to act as a spotter and a target for artillery. Most persons would need to pass a Fear(2) check to use this action. It is extremely easy to hit the target if the spotter/target has a good way to communicate his position to the aimer; such as using identical maps, sharing a hivemind or by being connected to the same combat-cognigator grid. Even a flaregun can work in a pinch. This action gives a +30% bonus to any following Artillery Aiming roll targeting this individual. It sometimes happens that a medal is handed to an imperial officer as reward for issuing this command. It is much more comon that the medal is handed to the officers next of kin. It is of course possible for an officer to call in fire on a position that is nearby, but not right on yourself. In that case you only count as an ordinary spotter, and rarely gain any medals.

Yes, I know this skill breaks the standard way of handling shooting weapons. It might even be a bit too complicated. But I do believe that indirect aiming of artillery is pretty tricky and different from direct aiming of any handheld or even tripod-/vehicle mounted gun that has the classical "line up towards the enemy" design. Not that I've ever had the luxury of shooting artillery myself... Maybe there is someone with some practical knowledge here?

Things like starshipmounted lasers and zero-g artillery would probably not be covered by Artillery Aiming, since they fire more directly. Part of me would like to have some rules for things like spread pattern artillery carpets fired by several batteries at once, but I do honestly believe that that should be more of a story telling element, with maybe a general Artillery Aiming roll to see roughly how it went.

What do you think?

Talking RT, Heavy Weapons; Artillery and Tanks:

I would go for the following:

If it ins mounted inside a vehicle with a sophisticated target system (like a modern aircraft), no talent is needed. You just role BS.
If it is inside a vehicle but there is no such system (like inside a WW-II aircraft) you will need the corresponding heavy weapon talent
If you hold it in your hands or if it is on a bi-pod or tri-pod before you, you will need the talent.

I would see a need for seperate rules for artillery... if I would see a need for incorporating the use of artillery in the game.
Frankly, the times where my pc will need "portable heavy weapons" will be slim enough.

The reason DH does not have Weapon Training (Ordinance) as a trainable trait is a matter of scale. Sure, if you are serving in an Imperial Guard artillery division during a planetary siege then this is a relavent skill. When it comes to "James Bond with a bolter" type plots it is more or less irrelevant. Even if a mission takes some acolytes undercover in the abovementioned artillery unit they would be more focused on rooting out whatever information they need from some trooper's tent than actually crewing the big guns. Keep in mind that more or less anything smaller than the main cannon on a Shadowsword can reasonably be covered by existing heavy weapon talents. Also, removing BS from ranged combat calculations is a really bad precident. Next thing you know Assassins and Scum will be arguing that gunfire is a matter of eye-hand coordination, and therefore AGILITY! While this has some merit in real life, the game rules already have an attribute that explicitly covers accuracy with ranged attacks.

You will also note that Techpriests cannot spend a few xp to train Pilot (Titan) despite the fact that all Legio Titanicus crews are Adeptus Mechanicus. This is not an omission for DH either. If you were a Moderatii or Princeps crewing a God-machine then you would not be working for the Inquisition! The Mechanicus would rather see such valuable members DEAD than serving another institution. No, I am not exagerating here. "Knowledge is power. Guard it well!"