Roles for players during a siege

[Hal]

My players are going to be leading an army in a siege of an enemy city. My plan is to handwave the encounters between large groups of soldiers; I don't particularly feel like playing those portions out. What I intend is for my players to act as a surgical strike team for their army, slipping in and swiftly dealing with matters that can't be handled by the main body of forces because they're too busy, too cumbersome, or simply not skilled enough to deal with.

Except, besides the inevitable "slip in and kill the ruler," I'm having trouble coming up with tasks for the players. Any suggestions?

[BayardSPSR]

Opening gates is a big one, but that could end the siege in one easy step (it has many times in real life). You might want to look at mining and counter-mining for inspiration, too - the original underground combat.

Poisoning wells, destroying or stealing supplies, gathering information on weak points, spreading rumors and propaganda to bring about surrender... It's all an option, but just opening a gate is the biggest weapon in their arsenal.

[Yakk]

D&D dungeon-crawls where apparently originally inspired by small strike teams getting into the dungeons under a castle via mine-shafts from the outside in war games. You'd mine under the walls, break into the dungeons, fight your way through them, and open the gates.

The defenders in a fantasy game would have dungeons they'd fill with monsters (like skeletons) and seal in. Opponents fighting their way up would have to fight these undead sentries, possibly alerting the mortal defenders.

...

So #1: Breaking in, via mines, into some dungeons/sewers.

#2: Making contact with agents within the city. Some of whom could be double-agents. (simply attacking the gates isn't practical, as they are well guarded)

#3: Arranging for a distraction.

Open a gate/Lower a harbor-chain.
Kill the king.
Kill a commander.
Kidnap a royal heir.
Rescue a hostage.
Kidnap a loved relative of the commander, and blackmail.

[Adoendithas]

Undermining often involved collapsing the tunnels to bring down the walls, which could lead to some good time-limited encounters ("Okay, you light the fuse. You have ten rounds to get out before the ceiling falls.").

[shamgar001]

A gate-opening mission wouldn't necessarily end the siege if the target castle has both an inner and outer wall.

Maybe the besieged castle seems to be getting supplies in from the outside. The party must figure out how the supplies are getting in (secret tunnel to the woods, perhaps).

The siege commander could also send the party to nearby villages to scout, steal supplies, or convince the inhabitants to support their soon-to-be new rulers.

Maybe the party would need to sneak in ahead of time to sabotage the equipment, poison the soldiers, or capture the commanding officer.