Given the question: Dolfijn-class submarine -  The Dolfijn class submarines of the Royal Netherlands Navy are a class of four submarines the Dolfijn Zeehond Potvis and Tonijn Which were built in the late 1950s and the early 1960s. They were the first indigenous submarines built for the Netherlands Navy after World War II. Given a choice of categories company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, the text refers to which one?
The answer is:
Mean Of Transportation