The Royal Navy's T class (or Triton class) of diesel-electric submarines was designed in the 1930s to replace the O P and R classes. Fifty-three members of the class were built just before and during the Second World War where they played a major role in the Royal Navy's submarine operations. Given a list of categories: company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, what category does the paragraph belong to?
Mean Of Transportation