SM UB-56 was a German Type UB III submarine or U-boat in the German Imperial Navy () during World War I. She was commissioned into the Flanders Flotilla of the German Imperial Navy on 19 July 1917 as SM UB-56.
She operated as part of the Flanders Flotilla based in Zeebrugge. UB-56 was sunk at 23:41 on 19 December 1917 at after striking a mine, 37 crew members lost their lives in the event.
She was built by AG Weser, Bremen and following just under a year of construction, launched at Bremen on 6 June 1917. UB-56 was commissioned later that same year . Like all Type UB III submarines, UB-56 carried 10 torpedoes and was armed with a deck gun. UB-56 would carry a crew of up to 3 officer and 31 men and had a cruising range of . UB-56 had a displacement of while surfaced and when submerged. Her engines enabled her to travel at when surfaced and when submerged.