Early Campaign

[DEB8]

You will have the message that your besieged garrison sorties out. Of course it will do it to join the relieving force it will see from the high battlements of your stronghold.

I find that the besieged force only joins the relief force on the battlefield when the relief force is less than 16 units. The besieged units usually join in ( as reserves ) eventually, when your army loses some of its original 16 units. Sometimes they will NOT sally out at all ! But you can forestall this latter problem by creating a Group of the Castle's units and dragging them out of the castle and onto the province / map ; thus forcing them to join the attack. NB : This tactic may even get them into the battle as part of the 16 units you start with...