Is there a class or set of feats that focuses on shooting with the ballista?

I’ve tried to do a little research, as my players will soon fight pirates, whose warship is armed with ballistas (gunpowder hasn’t been invented yet). Unfortunately, I was unable to find any class that would exactly fit the role of a ballista operator.

Is there a class that gets bonuses for attack, damage or some other useful features for ballistae? The pirates should be around 12th–14th level.

I use ballista rules from Heroes of The Battle, both heavy and light.

If there are some useful feats for that, please do not hestitate to mention it. As far as I have found I have:

  • ballista proficiency
  • crossbow sniper
  • plunging shot
  • ranged weapon mastery

Materials from 3.0, 3.5, Dragon Magazine and Dungeon Adventures are allowed.

Just to clarify, as the gamemaster, I do define ballista as an oversized variation of crossbow, thus most of feats, classes or features that affect crossbows will affect ballistae as well.

Can a ballista be fired once per round with a crew of three?

The rules for the ballista on p.255 of the DMG state that to make an attack the weapon must be loaded, aimed and fired. Each of these takes one action. However, could each of these actions be performed by a crew of three, with one character to perform each step, thus allowing the ballista to be fired once per round?

My assumption is yes, but there’s nothing textual to support this. Am I missing something?

Can Mage Hand be used to use a Ballista?

In the DMG page 255-256 are several siege weapons described which are actually objects. It takes actions to load, aim and fire the siege weapons. For the ballista for example it says:

It takes one action to load the weapon, one action to aim it, and one action to fire it.

I have always imagined you have to stand in 5 feet of the object and then take the "load", "aim" or "fire" action. In the decription for Mage Hand it says:

You can use your action to control the hand. You can use the hand to manipulate an object, open an unlocked door or container, stow or retrieve an item from an open container, or pour the contents out of a vial.

So technically the mage hand can manipulate an object but can it "load", "aim" or "fire" a ballista?

Can Vital Strike be used when firing a light ballista?

I am aware of this question regarding feats that can be used when firing a ranged siege engine and this question regarding whether Vital Strike can be used when firing slow-firing weapons. The answers to the first question do not discuss Vital Strike, while it is unclear whether the answers to the second question apply. I believe that the essence of this question boils down to:

  • Is firing a light ballista an Attack action?
  • Is there any other reason that a character firing a light ballista cannot use this feat to turn base damage of 3d8 into 6d8?

Regarding the first sub-question, I found it difficult to find any clear statements regarding what type of action is required to fire a siege engine. The best indication I could find was in an example on page 19 of the Players Guide to the Skull and Shackles Adventure Path (emphasis mine):

…If the same light catapult were instead crewed by three creatures, two could spend full-round actions aiming it and the remaining creature could fire it with a standard action.

If anyone is interested in the context, the character hoping to use the feat is an 8th level ranger with the Siege Engineer and Deadly Aim feats, employed as light ballista gunner on a pirate vessel. (I am already aware from the answers to this question that Deadly Aim and Vital Strike can be used in combination.)