In World War II she took part in the Norwegian Campaign, where she was damaged by German aircraft off Narvik on 28 May 1940. 10 sailors were killed and the ship was out of action for two months. In the Mediterranean she led the escort of a six cargo-ship convoy from Gibraltar to Malta, code named Operation Harpoon, which endured intense air strikes. The British squadron also faced the attack of an Italian light cruiser division in the Sicilia channel. Four merchantmen and two destroyers were sunk, while "Cairo" was hit by two 6-inch rounds from the Italian cruiser "Eugenio di Savoia", killing two members of her crew.