[1] For surface running, the boats were powered by two 500-brake-horsepower (373 kW) diesel engines, each driving one propeller shaft.

[4] Upon commissioning, Ro-109 was attached to the Sasebo Naval District and was assigned to Submarine Squadron 11 for workups.

[4] She arrived at Sarmi on 14 October, unloaded her cargo, and got back underway for her return voyage to Rabaul.

[4] However, she received orders to first perform lifeguard duty on 15 and 16 October 1943 for the crews of Mitsubishi G4M (Allied reporting name "Betty") bombers shot down off New Guinea, but she found no survivors.

[4] Ro-109 escaped damage and counterattacked, firing a spread of torpedoes at the destroyer USS Drayton (DD-366), but scored no hits.

[4][5] The picket line was tasked with providing warning of any move toward the Palau Islands by Allied invasion forces.

[5] When the Japanese 6th Fleet intercepted and decrypted an American signal on 27 May 1944 reporting the destruction of the submarines, it sent a warning message that prompted Ro-109′s commanding officer to move her to a new position 60 nautical miles (110 km; 69 mi) northwest of the area in which Ro-109 had been patrolling.

[4] At 14:20 on 23 December 1944, she was 490 nautical miles (910 km; 560 mi) east of Cape Eluanbi, Formosa, when her sound operator heard the propeller noises of a Allied task force.

[4] On 5 January 1945, she was 330 nautical miles (610 km; 380 mi) southeast of Cape Eluanbi when she made sound contact on a possible Allied convoy, but again she could not make an attack.

[4] At 18:00 on 16 February 1945 she sighted an Allied battleship and two cruisers escorted by a destroyers steaming northward 60 nautical miles (110 km; 69 mi) west of Lingayen Gulf.

At 10:00 on 13 April 1945 she got back underway to begin her tenth war patrol, bound for a patrol area in the Philippine Sea 20 nautical miles (37 km; 23 mi) south of Okinawa, where the Battle of Okinawa had been raging since 1 April 1945.

[4] The U.S. Navy fast transport USS Horace A. Bass (APD-124) was escorting a 17-ship convoy from Guam to Okinawa 165 nautical miles (306 km; 190 mi) south-southwest of Okidaitōjima when she detected a submerged submarine on sonar at a range of 1,250 yards (1,140 m) at 18:04 on 25 April 1945.

[4] She dropped five depth charges, and the submarine began to make radical evasive maneuvers and emit sound impulses to jam Horace A. Bass′s sonar.

[4] Horace A. Bass lost sonar contact after the depth charges exploded, then regained it at a range of 900 yards (820 m) and dropped five more depth charges, but the submarine — which Horace A. Bass′s crew assessed to be using German-made Bold sonar decoys — survived and dived deeper.

[4] Horace A. Bass made a final attack with six more depth charges, and before 20:00 debris and oil rose to the surface, indicating the sinking of the submarine at 21°58′N 129°38′E / 21.967°N 129.633°E / 21.967; 129.633 (Ro-109).

[4] On 7 May 1945, the Imperial Japanese Navy declared Ro-109 to be presumed lost off Okinawa with all 65 men on board.