In DoW do the colossal dragons strike anyone else as glass cannons?

Looking at the roster on p. 79 of the Battles book it sure looks like the venerable dragon might be an easy kill if you got some decently positioned missile units. Sure, the dragon can do a withdrawal from the first attack, but not the second since the dragon will be disordered. The stats for the colossal dragons look awesome except for that 1 UHP they have. Anyone have thoughts on how to keep such units alive in the face of missile armed troops?

That definitely bothered me at first. Then I came to the conclusion that it’s really just the way it would play out if you did a normal combat; the archers may need a nat 20 to hit, but you get 480 of them (4 units) and that dragon is taking an average of 22 hits a round for an average of 77 damage. He’s not gonna last long!

That said, in the specific case of the dragon, their special abilities may prevent this from being much of an issue. A fear aura can scatter the archers. It might be outright immune to nonmagical weapons. It might be able to polymorph itself and sneak into melee, then go on a rampage. And, of course, if it’s Ancient or Venerable, 100% chance of spellcasting, with a high enough level of casting power that it can cast Protection from Normal Missiles with no issue. (Not to mention plenty of other useful battlefield spells.)

So basically, yeah, it only has 1 UHP, but it probably shouldn’t be just sitting there and letting wave after wave of arrows hit it, unless it’s immune to them.

Aryxymaraki's analysis is spot on!

Don't field a Venerable Dragon that lacks Invulnerability without casting Protection from Normal Missiles on it. The cost of the spell (or even spellcaster!) is trivial relative to the cost of the dragon.

As a real world example, it would be akin to making sure you have some destroyers to protect your battleship from submarines...

Thanks for the analysis. I thought the math was correct, but it seemed to me that the way colossal monsters were scaled this made using them as a unit very vulnerable. I had not taken into account the options you mentioned above to make the dragon better protected. I think part of that is that I usually think of monsters in terms of their opposition being PCs. I would normally not think to make a dragon invulnerable to magic weapons since any party likely to go after a very old dragon will likely have magic weapons anyway. Viewing a dragon's opposition through the DoW lense, where much of the opposition is likely lots of normal men/demi-humans makes taking invulnerability to normal weapons a lot more appealing.

This is why you spend the 60k to get an entire unit of archers with +1 bows. Or have giant eagles on your side. Or both! 

The important thing is that yeah, dragons are more or less unkillable without a Designated Dragonslayer. 

Right! "Invulnerability to normal weapons" is actually a dragon power specifically for mass combat.

A single dragon with "Draconic Fear" and "Invulnerable to Normal Weapons" will annihilate an entire army if left unchecked by heroes or magic.

Draconic Fear causes a threatened unit to flee. Units with less than 1HD (meaning all except veteran human troops) receive no saving throw, and even veteran troops are unlikely to save. The fear will usually continue until the unit flees the battlefield. Dragons are not themselves threatened by non-flyers, so the dragon is free to position itself in order to maximize its threat.

It's really just brutal.