sentences:  There were two mostly cosmetic sub-types of the class, sometimes referred to as classes themselves
  
  This subclass was identical but had only one stack rather than two, and consisted of "YMS-135", "YMS-445", "YMS-480", and "YMS-481".This subclass was also identical but had no stacks, and comprised "YMS 446"–"YMS 479".Eighty vessels of the class were ordered from US yards for transfer under Lend-Lease to the United Kingdom as the BYMS-class minesweeper.