Sister ships Thomson Spirit and Thomson Cleebration, (later with the prefix Marella replacing Thomson) were originally ordered by the Swedish Johnson Line as container ships. Somewhere along the planning/building process the order was cancelled and the order was taken over by Holland America Line. Both were completed as passenger liners to be used on the North Atlantic and cruising.
The basic hull design is that of the originally proposed container ships. I believe that the two original Sulzer main engines were also retained for their new careers.