(Kaichu type submarine scanned from "Submarines
of the Imperial Japanese Navy" by Polmar and Carpenter)
IJN Submarine RO-46:
Tabular Record of
© 2001-2011 Bob Hackett & Sander Kingsepp
23 May 1943:
13 June 1942:
Kobe. Laid down Mitsubishi Shipbuilding as a 960-ton type K6 submarine.
Launched and designated RO-46.
20 January 1944:
Lt (later LtCdr) Suzuki Shokichi (62) (former CO of RO-68) is posted Chief Equipping Officer.
19 February 1944:
Completed and attached to the Maizuru Naval District. LtCdr Suzuki is the Commanding Officer.
28 March 1944:
Arrives at Tokuyama Fuel Depot. Refuels.
29 March 1944:
2 April 1944:
Off Minase Light, Iyo Sea. During a working-up cruise, RO-46 collides underwater with I-46 that suffers damage to her conning tower.
3 April 1944:
At 0430, USN codebreakers intercept and decrypt a message that reads: "1. While this unit was carrying out picket patrol duty 2 April, I-46 and RO-46 had underwater collision at 2145, ---- distance to southwest of Kominasa Light. 2. Damage summary: I-46, 2 periscopes damaged. Part of ----- slightly damaged. RO-46 ---- (blanks) ---- diving (planes?) damaged. (Expect docking will be necessary).”
13 June 1944: Operation "A-GO" - The Defense of the Marianas:
Admiral Toyoda Soemu (33)(former CO of HYUGA), CINC, Combined Fleet, activates A-GO and orders Vice Admiral (Admiral, posthumously) Takagi Takeo (39)(former CO of MUTSU), CINC, Sixth Fleet (Submarines) to redeploy his boats to the E of the Marianas.
15 June 1944: American Operation "FORAGER" - The Invasion of Saipan, Marianas:
Vice Admiral (later Admiral) Richmond K. Turner's (USNA ’08)(former CO of ASTORIA, CA-34) Task Force 52 lands Marine LtGen Holland M. Smith's V Amphibious Corps and the invasion begins. Communications between Takagi's Sixth Fleet on Saipan are disrupted by the invasion. Command of the Sixth Fleet's submarines passes to ComSubRon 7's Rear Admiral Owada Noboru (44)(former CO of YAMASHIRO) at Truk. He orders most of the Sixth Fleet's submarines to withdraw from the Marianas.
23 June 1944:
RO-46 is reassigned to SubDiv 34, Sixth Fleet. Departs Kure for the Saipan area on her first war patrol.
3 July 1944:
Damaged in an attack in the Saipan area.
8 July 1944:
Returns to Kure for mechanical repairs.
19 September 1944:
Departs Kure for an area SW of Palau on her first war patrol.
28 September 1944:
SW of Palau. RO-46 sights an American carrier, but the distance is too far for an attack.
1 October 1944:
LtCdr Suzuki sights another carrier, but fails to attack. 
2 October 1944:
LtCdr Suzuki is ordered to reconnoiter the American fleet anchorage at Ulithi. RO-46 reconnoiters Ulithi from the western direction and I-177 from the east. The reconnaissance is a part of preparations for the first Kaiten attack on Ulithi.
7 October 1944:
Carries out a periscopic observation of Ulithi. RO-46 reports the presence of USS BUNKER HILL (CV-17), two heavy cruisers and their escorts in the anchorage.
13 October 1944: Operation "SHO-I-GO" - The Defense of the Philippines:
Admiral Toyoda Soemu, CINC, Combined Fleet, orders the SHO-I-GO plan activated.
14 October 1944:
Returns to Kure.
20 October 1944-30 June 1945: American Operation "KING TWO" - The Invasion of Leyte, Philippines:
Admiral (later Fleet Admiral) William F. Halsey's (USNA ’04)(former CO of SARATOGA, CV-3) Third Fleet of 738 ships including 18 aircraft carriers, six battleships, 17 cruisers, 64 destroyers and over 600 support ships land the Army's X Corps (24 th Infantry and 1st Cavalry Divisions) and the XXIV Corps (7th, 77th and 96th Infantry Divisions) that begin the campaign to retake Leyte.
RO-46 departs Kure on her on her third war patrol to an area E of the Philippines (B Group).
7 November 1944:
The CINC, Sixth Fleet, Vice Admiral Miwa Shigeyoshi (39)(former CO of KINU) orders all submarines in the Philippines area to return to Japan.
13 November 1944:
On her way back, RO-46 rescues an IJAAF Nakajima Ki-43 Hayabusa ("Oscar") pilot, of either the 20th or 33rd Sentai, downed in a battle over Manila.
19 November 1944:
Returns to Maizuru.
9 December 1944:
Lt Tokunaga Masahiko (67)(former CO of RO-64) is appointed CO.
8 January 1945:
Departs Kure for the area W of Luzon on her fourth war patrol.
9 January 1945: American Operation "MIKE ONE" - The Invasion of Luzon, Philippines:
Vice Admiral (later Admiral) Thomas C. Kinkaid's (USNA ’08)(former CO of INDIANAPOLIS, CA-35) Task Force 77 lands almost 175,000 men of LtGen (later General) Walter Krueger's Sixth Army at Lingayen Gulf under cover of heavy gunfire from Vice Admiral (later Admiral) Jesse B. Oldendorf's (USNA ’09)(former CO of HOUSTON, CA-30) TG 77.2 bombardment force and aircraft of Rear Admiral (later Vice Admiral) Calvin T. Durgin's (USNA ’16) TG 77.4. The Sixth Army begins the campaign to retake Luzon from General Yamashita Tomoyuki's 14th Area Army's defenders.
29 January 1945:
W of Iba, Luzon. RO-46 torpedoes and damages transport USS CAVALIER (APA-37) at 14-48N, 119-18E. CAVALIER is towed to Leyte.
30 January 1945:
The attack takes place at 0133. LtCdr Tokunaga reportssinking an oiler from a convoy, then departs the area. 
2 February 1945:
Vice Admiral Miwa orders RO-46, RO-112, RO-113 and RO-115 to proceed to Apari, Philippines to evacuate stranded IJNAF pilots.
4 February 1945:
Arrives at Takao, Formosa. According to the new orders, each of the submarines must carry a shipment of ammunition and fuel destined for troops on Luzon. RO-46 is ordered to evacuate at least 40 pilots and proceed directly to Sasebo thereafter.
7 February 1945:
Departs Takao to rescue stranded pilots from Batulinao in northern Luzon.
10 February 1945:
About 2400 (JST), RO-46 rendezvouses with Imperial Army-operated Daihatsu barges off Batulinao. She embarks 46 airmen in return for her cargo. Departs Batulinao.
12 February 1945:
Returns to Takao.
13 February 1945:
Departs Takao for a reconnaissance mission to the Nansei Shoto area.
19 February 1945:
Arrives at Kure. Lt Kimura Masao (63)former CO of RO-50) is assigned as CO.
1 April 1945: American Operation "ICEBERG" - The Invasion of Okinawa:
Vice Admiral (later Admiral) Raymond A. Spruance's (USNA ’06)(former CO of MISSISSIPPI, BB-41) Fifth Fleet, including more than 40 aircraft carriers, 18 battleships, 200 destroyers and over 1,000 support ships surround Okinawa. LtGen Simon B. Buckner Jr's Tenth Army (7th, 77th, 96th Infantry, 1st, 6th Marine divisions) makes amphibious landings and begin the campaign to take the island from LtGen Ushijima Mitsuru's 32nd Army's defenders.
6 April 1945:
Departs Kure for the for an area NE of Kita-Daito Jima on her fifth war patrol.
17 April 1945:
Southern Ryukyu Islands. RO-46, under LtCdr Kimura Masao, makes a report to Sixth Fleet from an area 60 nm NE of Kita-Daito-Jima. This is the last signal received from Kimura.
29 April 1945:
USS TULAGI (CVE-72) is on antisubmarine operations along the shipping lanes approaching Okinawa. Aircraft of TULAGI's Composite Squadron VC-92 possibly sink RO-46 at 24-15N, 131-16E. 
2 May 1945:
Presumed lost with all 86 hands in the Okinawa area. Lt Kimura is posthumously promoted two ranks to Cdr.
10 June 1945:
Removed from the Navy List.
 Author and historian Kimata Jiro suggests the carrier could have been one from TG 38.4 or from TU 32.7.
 Some sources claim RO-46 was sunk on 18 April 1945 NE of Wake Island by USS SEA OWL (SS-405), but the target in that case was I-372 that was not sunk in the attack. RO-46 was nowhere near Wake at that time, but I-372 was there.
Thanks go to Dr. Higuchi Tatsuhiro of Japan and to Matt Jones for additional CO info.
Thanks also go to John Whitman of the USA for info on CNO intercepts of Japanese messages.
– Bob Hackett and Sander Kingsepp.
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