J21 or J-21 may refer to: Vehicles Aircraft Junkers J 21, a German reconnaissance aircraft SAAB J 21, a Swedish fighter Shenyang J-21, a Chinese prototype fighter Soko J-21 Jastreb, a Yugoslav light attack aircraft Locomotives LNER Class J21, a British steam locomotive class Ships , a Bangor-class minesweeper of the Royal Navy and Royal Canadian Navy , an Östergötland-class destroyer of the Swedish Navy , a survey ship of the Indian Navy Other uses Bronchiolitis County Route J21 (California) Elongated pentagonal rotunda, a Johnson solid (J21)