This is the Italian liner SS Andrea Doria. The Continental-size (4-3/16 x 5-7/8″) postcard was mailed from Gibraltar on January 17, 1955. One year and seven months later, this ship went to the bottom, 160 feet down, off the coast of Massachusetts, after a collision with the MS Stockholm of the Swedish American Line. The story is here.
Uncle Bob's Pix 