[Note 1] In nine patrols UC-26 was credited with sinking 39 ships, either by torpedo or by mines laid.

On 16 February 1917, SM UC-26 was rammed by the Royal Naval vessel Mona's Queen (with over 1,000 troops embarked) near Le Harve.

She had a dive time of 48 seconds and was capable of operating at a depth of 50 metres (160 ft).

When submerged, she could operate for 53 nautical miles (98 km; 61 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 9,260 nautical miles (17,150 km; 10,660 mi) at 7 knots (13 km/h; 8.1 mph).

UC-26 was fitted with six 100 centimetres (39 in) mine tubes, eighteen UC 200 mines, three 50 centimetres (20 in) torpedo tubes (one on the stern and two on the bow), seven torpedoes, and one 8.8 cm (3.5 in) Uk L/30 deck gun.