[Note 1] UB-128 was surrendered to the Allies at Harwich on 3 February 1919 in accordance with the requirements of the Armistice with Germany.

After passing into British hands, UB-128 was towed to Falmouth along with five other U-boats [Note 2] for use in a series of explosive test trials by the Royal Navy in Falmouth Bay, in order to find weaknesses in their design.

Following her use on 1 February 1921, UB-128 was dumped on Castle Beach and sold to R. Roskelly & Rodgers on 19 April 1921 for scrap (for £120), and partially salvaged over the following decades, although parts remain in situ.

Like all Type UB III submarines, UB-128 carried 10 torpedoes and was armed with a 10.5 cm (4.13 in) deck gun.

UB-128 would carry a crew of up to 3 officer and 31 men and had a cruising range of 7,280 nautical miles (13,480 km; 8,380 mi).