 At the beginning of World War I , she was one of only four operational submarines in the Austro @-@ Hungarian Navy . On 22 August 1914 , U @-@ 3 began operating reconnaissance cruises out of the naval base at Brioni , but moved a month later to Cattaro . In April 1915 , a 3 @.@ 7 @-@ centimeter ( 1 @.@ 5 in ) quick firing ( QF ) deck gun was added . 
