25th Year
25th Year is a three mission mini-campaign for Descent: Freespace, a.k.a. Freespace 1, originally created by KolChak. The mission can be found by searching for 25thyear.zip. The campaign is neither VP packed nor voiced. It contains no mods and will work alongside almost any installed campaigns.
Storyline
Consisting of merely three missions, the story is quite simple; you must stop the Hammer of Light from aquiring shivan technology. The HOL have captured an Orion class ship, the GTC Riser, which was carrying shivan technology. Your wing is being sent in to destroy both the captured vessel plus all hostiles. The rest of the campaign consists of mopping up HOL cargo depots.
Tips
Mission 1: Stolen Orion
As with pretty much every assault on a ship of cruiser class or above, lure the enemy fighters away from the vessel. This will make taking them down a bit safer. When the enemy wings are down, obliterate the GTC Riser.
Mission 2: Cargo Assault
A couple of Aten class enemy ships, four of them, make your job a bit hectic in this mission. To make life somewhat easier, take out the Ankh's early on. This will make the mission easier on your shields.
Mission 3: Surprise Bash
A deceptively simple intro will not prepare you for the Cain and Dragon class ships that will arrive when you least expect them. Take out the Ankh guns before the bad guys arrive. If you don't, you'll wish you did.
Availability
The campaign can still be found in the Volition Watch Archives. The Volition Watch Archives are not actively maintained anymore, however, so the campaign might not be available. The VWA requires an account, so if you do not have one, you will have to look for it elsewhere.