"Floating Prisons"

We've seen a few passing mentions of US using navy ships to house detainees, but this is probably the most complete information coming from the human rights group Reprieve.

From previous mentions, I have little doubt that the core of this is true, that detainees were held and interrogated aboard US vessels, but the details, as they come out, will matter. Was this a temporary local fix in areas where the US had no facilities or were the detentions long term? Were the ships chosen specifically because there was no oversight and no limits? Are these detentions another effort to get around torture and detention laws, another "secret prison" system, or were these just brief in theater fixes?

The "what" sounds pretty ugly, but I think the "why" will tell us more.