Built at Kure Navy Yard. Laid down as Submarine No. 159 on November 11, 1941.
Launched on May 2, 1942. Assigned to LtCdr Ohashi Katsuo on February 20, 1941. Completed and comissioned on May 24, 1943, assigned to Sasebo Naval District, SubRon 11. On August 20, 1943 assigned to SubDiv 22, SubRon 3.
On August 25, 1943 departs Kure arriving at Truk on September 1, 1943. On September 7, 1943 departs Truk bound for Espiritu Santo for her first war patrol. On September 15, 1943 assigned to the 6th Fleet.
30 September 1943:
Patrols off Cape Esperance. No enemy vessels sighted. The I-181 is then redirected to the Torres Strait.
2 October 1943:
Arrives at the Torres Strait.
14 October 1943:
Torres Strait. Cdr Ohashi attacks a convoy twice but fails to score any hits.
20 October 1943:
Returns to Truk.
11 November 1943:
Departs Truk for the Bougainville area on her second war patrol.
12 November 1943:
Reassigned to Vice Admiral, the Baron, Samejima Tomoshige's (former CO of NAGATO) Eighth Fleet/Southeast Area Fleet based at Rabaul.
24-25 November 1943: The Battle off Cape St. George:
50 miles E of Cape St. George, New Britain. Destroyers AMAGIRI, YUGIRI, ONAMI, MAKINAMI and UZUKI are on a troop transport run to Buka, off Bougainville. They are intercepted by Captain (later Admiral/CNO) Arleigh A. Burke's DesRon 23. YUGIRI is sunk by gunfire by USS CHARLES AUSBURNE (DD-570), CLAXTON (DD-571) and the DYSON (DD-572) at 04-44S, 154 E. The same three American destroyers, joined by the SPENCE (DD-512) and CONVERSE (DD-509), sink MAKINAMI with torpedoes and gunfire and damage UZUKI. The Americans suffer no damage.
On November 26, 1943 I-181 rescues eleven survivors from Yugiri then three days later back to Rabaul.
On December 7, 1943 at 9:30am departs Rabaul abaord is 44 tons of cargo including four packages of code books, one package of light globes, two packages of type H ammunition and one package of type U ammunition bound for Sio. On December 9, 1943 arrives at Sio then attacked by bombers that drop 15 depth charges and cause I-181 to crash dive, but later the sub surfaces and delivers the cargo and doctor Tetsuo Watanabe then returns to Rabaul.
11 December 1943:
At 0800, returns to Rabaul.
16 December 1943:
Arrives at Buka on her fist supply run there, unloads her cargo, then departs for Rabaul.
20 December 1943:
LtCdr (Cdr, posthumously) Taoka Kiyoshi (55) (former CO of RO-500) is appointed Commanding Officer.
21 December 1943:
Departs Rabaul on her second supply run to Buka.
22 December 1943:
Arrives at Buka but fails to deliver her cargo.
1 January 1944:
I-181 is redirected to the area N of Choiseul to intercept an enemy task force.
2 January 1944: American Operation "Michaelmas"- The Invasion of Saidor, New Guinea:
Rear Admiral (later Vice Admiral) Daniel E. Barbey's Task Force 76 lands the Sixth Army's 126th Regimental Combat Team of the 32d Division at Saidor and by-passes the Japanese garrison at Sio, 75 miles east.
On January 3, 1944 I-181 was returning from a New Guinea supply mission to Rabaul. In the Saint George Channel the submarine spotted and rescued Major Gregory "Pappy" Boyington after he ditched F4U
Corsair 17915 then proceeds to Rabaul.
6 January 1944:
Departs Rabaul on her third supply run to Buka.
7 January 1944:
Arrives at Buka, unloads her cargo.
8 January 1944:
Returns to Rabaul.
13 January 1944:
Departs Rabaul on a supply run to Gali, New Guinea in company of RO-104, carrying ComSubDiv 22, Capt Maejima Toshihide (48) and his staff. I-181's estimated time of arrival at Gali is 16 January, but she remains MIA thereafter.
16 January 1944:
Vitiaz Strait. That evening, I-181 is intercepted and sunk in a running battle with an unidentified American destroyer and a PT boat. Her demise is witnessed by the Japanese garrison at Gali. 
On March 1, 1944 sunk southwest of New Guinea with the entire crew of 89 aboard. Officially removed from the Navy list on April 30, 1944.
Combined Fleet - IJN Submarine I-181: Tabular Record of Movement
The Naval Land Unit That Vanished In The Jungle mentions the December 7-9, 1943 mission to Sio
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May 22, 2017