Costa Diadema cruise ship in the port of Palma de Mallorca. Costa Diadema is a Dream-class cruise ship operated by Costa Crociere. It is the largest vessel flying an Italian flag and currently Costa Crociere`s flagship. It was launched on 15 November 2013. It is 306 m 1,003 ft 11 in long and has a capacity of 3,693 passengers