[Note 1] In nine patrols UC-34 was credited with sinking 21 ships, either by torpedo or by mines laid.

On 30 December 1917 under the command of Oberleutnant zur See Horst Obermüller, UC-34 torpedoed the British troop ship HMT Aragon off the Port of Alexandria.

[4][5] Aragon's escort, the destroyer HMS Attack, rescued 300 to 400 survivors but then UC-34 torpedoed and sank her as well.

She had a dive time of 35 seconds and was capable of operating at a depth of 50 metres (160 ft).

When submerged, she could operate for 54 nautical miles (100 km; 62 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 10,180 nautical miles (18,850 km; 11,710 mi) at 7 knots (13 km/h; 8.1 mph).