(This place has been a little too quiet...)

Welcome back Commander. We've called you here for a pressing matter. You've been away for far too long anyways.

It seems as if the ponies have just finished dealing with problems of their own. Said problem was expelled from their country northwards...

Of course, you know what's the northward boundary of Equestria, right?

They've just neared one of our outposts, and we don't like it. It's a small fortress for patrol purposes and border control, but it's got enough griffons to stop a nice sized force.

Luckily, griffon patrols are just itching for something live to slash at. Some of them have even stopped bothering to practice sword skills. Said they'd rather have a go with talons. We'll see about that.

Equestrians have shared knowledge with us over the years, and this is what we're coming up against- some things called changelings. Uh, simplified, they're like bugs.

I'm sure you've figured out what the objective is by now.

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There is a small fortress stationed near the southern border of the Kingdom. It is the closest to the positions of the changelings, and they appear to be readying for an attack, or at least heavy scouting.

It rests on top of a low hill overlooking a thin forest of evergreens. The forest only begins to thicken 1 mile out. There is good visibility within this radius.

Considering the peacetime as well and the little need for heavy artillery facing our Equestrian neighbors, this fort is armed only with 2 trebuchets, 4 catapults, and 8 ballistae.

The trebuchets sit outside the fort.

The fortress has substantially strong stone walls, built to repel heavy artillery. There is no threat of breaching the wall. The top floor is open and has the catapults mounted along with 6 ballistae. There is a floor below it with large firing windows spanning the fortress wall allowing the 2 other ballistae to fire from them.

The outpost has 70 heavy griffon infantry ready to fight.

Recap:
70 Heavy Infantry
2 trebuchets
4 catapults
8 ballistae

(Note: Artillery crews are not counted)

Observation flights report:

The changelings are positioned south, out of range of the trebuchets.

It seems as if they want to start wearing down the fort and eventually just wipe it out.

Changeling numbers are at:
50 Drones
180 Hatchlings
20 Warriors
5 Deceivers

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Well. I think they're ready to attack. Time to squash some pony-sized bugs.

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The enemy strategy will be to attempt to completely surround the fort, increasing the difficulty of defense. They are currently approaching.

538382

(This place has been a little too quiet...)

I've just been waiting for someone to attempt my last scenario.

And I'm not sure what to make of your scenario. Either I'm missing something or you intended it to be more complicated than it is. It would seem like the only logical course of action would be hole up inside the fortress and try to whittle their forces down with our artillery as they come within range.

The trebuchets sit outside the fort.

Well I see no way to move them inside the fort so i suppose that after inflicting some damage on the aproaching enemy, once the enemy closes to within a certain distance, I'll have the trebuchet crews burn their trebuchets, so that the enemy couldn't capture and use them, and retreat inside the fortress. There we will wait for reinforcements while we whittle away at them with our ballistae and catapults.