 After initially operating out of Pola , U @-@ 20 was transferred to Trieste in February 1918 . Over the next three months , the U @-@ boat patrolled in the northern Adriatic between the Tagliamento estuary and Venice . U @-@ 20 had an encounter with an enemy submarine on 7 April but was not able to successfully launch an attack . On 3 July , Linienschiffsleutnant Ludwig Müller sailed U @-@ 20 out from Trieste for the Gulf of Venice . A day later , U @-@ 20 was spotted by the Italian submarine F @-@ 12 , which was on patrol in the northern Adriatic . F @-@ 12 initially pursued U @-@ 20 underwater , and then on the surface . At a range of 650 yards ( 590 m ) , F @-@ 12 torpedoed U @-@ 20 at position 45 ° 29 ′ N 13 ° 05 ′ E , sinking her with all hands . There was no wreckage on the surface , only an oil slick . Like all of her sister boats , U @-@ 20 had no wartime successes . 
