Prefix: Sub-

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Across
  1. 3. a vehicle that travels under water
  2. 4. to bring under control
  3. 5. a passageway under the ground; an electric underground railway
  4. 6. a title under the main title of a book, or lines of dialogue on the television
  5. 8. to put under water
Down
  1. 1. a person who is under someone else in rank or importance
  2. 2. to put under someone else’s control
  3. 4. to go down to a lower level, like with water
  4. 5. a small group that is under a larger group
  5. 7. below the freezing point