Damocles was Kang's time warship. Kang used it to travel through time, and to different planets to conquer them in case his future gets wiped out.
The Avengers, however, infiltrated his ship and put an end to the invasion once and for all. S.H.I.E.L.D. later occupied the Damocles and used it for their new space headquarters besides the Helicarrier.
It is now the headquarters of S.W.O.R.D., an organization that deals with various extraterrestrial threats.
It was destroyed during the Skrull Invasion. Its remains were floating in space after the post-Skrull invasion.
The massive ship possess the most advanced weaponry and time drives from the 41st Century. It also has an advanced A.I. It's most powerful attack was deflected back by Thor's magic.