Ye it was requisitioned and quickly retro fitted to do this job. Before it was a merchant container ship.
And as AM said, they are two different versions of the Harrier. The first is the FFA (Fleet Air Arm, Royal Navy's Air Force) Sea Harrier FRS1 (the grey one with black nose) which is primarily a fighter (although did a little bit of ground attack in the Falklands, mainly at the very start hitting Stanley airport) and the second is the RAF Harrier GR3, which is primarily a ground attack aircraft, and has a very long pinokio nose
Sea Harrier FRS1:
Harrier GR3:
Both will be featured in PR Falklands, but both will only (for now at least), be reskins of the Harrier GR9.