O-class submarine

O-class submarine may refer to:


 * United States O-class submarine
 * Oberon-class submarine
 * Odin-class submarine
 * Several early submarine classes of the Royal Netherlands Navy:
 * O 1-class submarine consisting only HNLMS O 1
 * O 2-class submarine
 * O 6-class submarine consisting only HNLMS O 6
 * O 7-class submarine consisting only HNLMS O 7
 * O 9-class submarine
 * O 12-class submarine
 * O 16-class submarine consisting only HNLMS O 16
 * O 19-class submarine
 * O 21-class submarine