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

[4] Early on the morning of 29 June 1943 she sighted what her commanding officer identified as a large transport and began to pursue it.

[4] She resurfaced two hours later and resumed her pursuit of the transport, but ultimately discontinued the chase when she identified it as a neutral Soviet merchant ship.

[4] Ro-104 departed Rabaul that day to begin her third war patrol, ordered to attack the landing force.

[4] Ro-104 got underway from Rabaul on 23 September 1943 for her fourth war patrol, ordered to join the submarines I-174 and I-177 in intercepting and attacking United States Navy Task Force 76 in the vicinity of Finschafen on New Guinea′s Huon Peninsula.

[4] Ro-104 got underway from Rabaul on 9 November 1943 for her sixth war patrol, ordered to intercept and attack the damaged U.S. Navy light cruiser USS Birmingham (CL-62).

[4] On 26 December 1943, Ro-104 put to sea from Rabaul for her fourth supply run to Sarmi, New Guinea.

[4] She encountered no Allied ships, and she departed her patrol area on 4 January 1944, returning to Rabaul later that day.

[4] Based on a message Submarine Squadron 7 transmitted on 12 January 1944 that it had intercepted and decrypted, Fleet Radio Unit, Melbourne (FRUMEL) — an Allied signals intelligence unit headquartered in Melbourne, Australia — provided the entire schedule for Ro-104′s voyage to Allied forces on the day of her departure.

[4] On 31 January 1944, Ro-104 departed Rabaul bound for Kure, where she arrived on 12 February 1944 to undergo repairs and an overhaul.

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

[4][6] On 18 May 1944, U.S. Navy signals intelligence personnel intercepted and decrypted Japanese signals indicating the formation of picket line "NA" between Truk and the Admiralties, and a hunter-killer group composed of the destroyer escorts USS England (DE-635), USS George (DE-697), and USS Raby (DE-698) departed Purvis Bay in the Solomon Islands to intercept the submarine I-16, then attack the submarines assigned to Scouting Line NA.

[4] Raby acquired radar contact on Ro-104 at a range of 4 nautical miles (7.4 km; 4.6 mi) at 06:04 local time.

[4] All three destroyer escorts then formed a ring around the probable location of Ro-104 in order to reestablish contact.

[4] After the second salvo, her crew heard a large underwater explosion and estimated that she had scored 10 to 12 hits on Ro-104 at a depth of 300 feet (91 m).

[4] While their boats recovered debris and oil samples from the water, the three destroyer escorts continued to search for Ro-104 until sunset in case she had survived, but found no sign of her.

[10][14] On 25 June 1944, the Imperial Japanese Navy declared Ro-104 to be presumed lost with all 58 men on board.