Titans, Vol. 1 #14A

Chain of Command
Aqualad receives a telepathic sending from Omen. It seems Vandal Savage captured her and forced information about the Titans from here, but unless someone intervenes, today is the day she'll die! He gathers the remaining Titans and they head underwater (sub courtesy of Aquaman, a wedding gift). Nightwing seeks advice on leadership and other matters from Batman, and gets it... sort of. The Titans confront Tartarus in their base deep under the sea, managing to free Omen but leaving Aqualad behind. Fortunately, Omen had a plan, and it works, sort of. Tartarus essentially defeats itself...
Release Date: 2000