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- Jastrząb (USA, then Poland): 800-ton United States S class submarine
- Jaskółka (Poland): 183-ton minesweeper
- Jen Shen (China): 300-ton gunboat
- Junín (Colombia): 120-ton coast guard vessel
- Jurmo (Finland): 400-ton tug
Read more about this topic: List Of World War II Ships Of Less Than 1000 Tons