UB-3 was ordered in October 1914 and was laid down at the Germaniawerft shipyard in Kiel in November. UB-3 was a little more than 28 metres (92 ft) in length and displaced between 127 and 142 metric tons (125 and 140 long tons), depending on whether surfaced or submerged. She carried two torpedoes for her two bow torpedo tubes and was also armed with a deck-mounted machine gun.