 Upon completion , U @-@ 20 began diving trials . On her 15 March 1917 trial , she was accidentally rammed by Admiral Spaun in the Fasana Channel . The collision with the Austro @-@ Hungarian light cruiser twisted U @-@ 20 's periscope , extensively damaged the conning tower , and knocked off her deck gun . After seven months of reconstruction , U @-@ 20 was commissioned into the Austro @-@ Hungarian Navy on 20 October . 
