The Second Battle of Second 14, thanks to the use of time travel, took place before the First Battle of Sector 14 or indeed before any other battle of the Second Shadow War. Using the temporal rift in Sector 14, the crew of the White Star - including Captain John Sheridan, Entil'Zha Jeffrey Sinclair, Ambassador Delenn, Commander Susan Ivanova, Ranger Marcus Cole, Lennier, and Zathras - went back in time to 2254 to stop the Shadows from destroying Babylon 4.
After receiving mysterious letters from over 900 years ago, both Sinclair and Delenn begin making preparations for their journey. Sinclair leaves Minbar for Babylon 5, while Delenn gets Sheridan to come with her to the White Star. There, they see historical records from the Great Machine and ancient Minbar that show Babylon 4 as the base of operations in the First Shadow War, as well as the attempt by the forces of the Shadows to destroy B4 in 2254. However, they were stopped by a familiar-looking ship: the White Star. Their mission was to go through time to save Babylon 4, then take it one-thousand years into the past. If they did not, the Shadows would be far stronger in this time because the forces of Light did not prevail then.
Upon traveling through the temporal rift, they find a group of Shadow Fighters escorting a high-yield thermonuclear weapon toward B4. They manage to take out several of the fighters, but they still get the weapon in range of the station. With no other option, Susan Ivanova fires on the weapon itself, detonating it and setting off a massive explosion accompanied by a powerful electro-magnetic pulse (EMP). The White Star manages to get away from the blast, and the explosion was still far enough away from the station to not cause any damage.
The crew of the White Star continues on to the station to complete their mission. Fortunately, all of B4's sensors were temporarily knocked offline by the EMP from the explosion, allowing them to get close and dock with the station. Unfortunately, the result of the blast saw Sheridan's time stabilizer damaged, making him "unstuck" in time and sending him forward to 2278. With Sheridan missing, Sinclair took command of the mission.