UB-45 was ordered in July 1915 and was laid down at the AG Weser shipyard in Bremen in September. UB-45 was a little more than in length and displaced between , depending on whether surfaced or submerged. She was equipped to carry a complement of four torpedoes for her two bow torpedo tubes and had an deck gun. As part of a group of six submarines selected for Mediterranean service, UB-45 was broken into railcar-sized components and shipped to Pola where she was assembled and then launched and commissioned in May 1916.