She was commissioned into the German Imperial Navy on 20 April 1918 as SM UB-126.

[Note 1] UB-126 was surrendered 24 November 1918 in accordance with the requirements of the Armistice with Germany.

Like all Type UB III submarines, UB-126 carried 10 torpedoes and was armed with a 10.5 cm (4.13 in) deck gun.

UB-126 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).

Her engines enabled her to travel at 13.9 knots (25.7 km/h; 16.0 mph) when surfaced and 7.6 knots (14.1 km/h; 8.7 mph) when submerged.