Maybe in a catamaran war story, the catamaran is involved in a chase. It could be chased by a larger and more powerful enemy ship. The crew of the catamaran has to use their sailing skills and knowledge of the local waters to outmaneuver the pursuer. They might lead the enemy ship into a shallow area where it gets stuck while the catamaran escapes.
A catamaran could be used to transport troops. It can move quickly and quietly, so it might be able to land soldiers on an enemy beach without being detected easily. For example, under the cover of darkness, a catamaran full of soldiers could approach the shore and launch a surprise attack.
Another possible event is that the catamaran is part of a blockade. It could be used to stop enemy ships from entering or leaving a port. The catamaran, with its agility, can intercept small supply ships trying to break the blockade. The crew might have to engage in brief skirmishes with the crews of these ships to prevent them from getting through.