Given the question: SM UB-31 -  SM UB-31 was a German Type UB II submarine or U-boat in the German Imperial Navy (German: Kaiserliche Marine) during World War I. The U-boat was ordered on 22 July 1915 and launched on 16 November 1915. She was commissioned into the German Imperial Navy on 25 March 1916 as SM UB-31.The submarine sank 26 ships in 25 patrols. UB-31 was depth charged and sunk by British warships HMS Lord Leitrim HMS Loyal Friend and HMS Ocean Roamer in the English Channel on 2 May 1918. 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