Pick one category for the following text. The options are - company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work. MO-class small guard ship -  The MO (Russian: Mалый Охотник Malyj Okhotnik; English: Small Hunter nickname Moshka(Fly)) is a class of small ships produced before and during World War II for the Soviet Navy. Their primary function originally was anti-submarine warfare. During the war they carried out many additional roles from supporting landing operations to escorting convoys. Over 350 ships were built.
The answer to this question is:
Mean Of Transportation