(Subchaser No. 46 by Takeshi Yuki scanned from "Color Paintings of Japanese Warships")

IJN Subchaser CH-50:
Tabular Record of Movement

© 2005-2015 Bob Hackett, Sander Kingsepp and Peter Cundall

Revision 3

15 April 1943:
Innoshima. Laid down at the Hitachi Zosensho shipyard as CH-450.

31 July 1943:
Renumbered CH-50.

4 September 1943:

30 November 1943:
Completed and registered in the Yokosuka Naval District. Assigned to the Yokosuka Guard Unit. Escorts convoys between Yokosuka and Kobe.

16 January 1944:
Izu Islands. CH-50 is escorting anti-submarine "Q" ship DELHI MARU and anti-submarine net layer TATSU MARU in heavy seas. At about midnight, Captain (later Rear Admiral) Karl G. Hensel's (USNA ’23) old USS SWORDFISH (SS-193) torpedoes and sinks DELHI MARU at 34-12N, 139-54E. Five crewmen and 135 troops are KIA. Her aft section keeps floating. The other ships attempt to tow it to Japan, but the next morning it capsizes and sinks in rough seas.

Late January 1944:
CH-50, CH-52 and minelayer SARUSHIMA depart Yokosuka escorting convoy No. 3125 OTSU consisting of KASAGI MARU and possibly others to Chichi-Jima.

9 February 1944:
At 0522 departs Saipan with minesweeper W-22, and auxiliary subchasers KYO MARU No. 10 and SHONAN MARU No. 8 escorting convoy No. 4127 consisting of MATSUE MARU, auxiliary storeship SHINYO MARU and YOSHIDA MARU No. 3.

10 February 1944:
At 1832 SHINYO MARU drops to the rear of the convoy due to mechanical failure.

11 February 1944:
At 1912 SHINYO MARU's mechanical failure is solved and the ship takes up her original position in the convoy.

12 February 1944:
At 1200 auxiliary subchaser KYO MARU No. 10 is detached and returns to Saipan. At 1700 auxiliary minesweeper TOSHI MARU No. 5 joins the convoy and starts escorting.

14 February 1944:
At 0338, arrives at Chichi-Jima.

3 March 1944:
At 1145 departs Chichijima escorting convoy No. 3225 consisting only of transport MITAKESAN MARU.

8 March 1944:
Arrives at Saipan.

1 April 1944:
At 1100, CH-50 departs Tokyo as part of the escort of convoy Higashi-Matsu No. 4. The ships and their destinations are: Saipan: SHOUN, TOKO, TAKASAN, AKIKAWA, KOKO, SHIRAMINE, TAIKAI, KAKOGAWA and MACASSAR MARUS. Guam: MIMASAKA, TOAN, AZUCHISAN and NISSHU MARUs and UNYO MARU No. 8 Truk: Fleet supply ship KINESAKI, SHOZUI, TATEBE, SHIMA, SHINYO and HAVRE MARUs. Palau: Fleet supply ship MAMIYA, TENRYUGAWA, TAIAN and TOSEI MARUs and SHINSEI MARU No. 5 Yap: SHINSEI MARU.The convoy commander is Rear Admiral Kiyota Takahiko (42) (former CO of NACHI) in destroyer SAMIDARE. The other escorts include destroyer ASANAGI, torpedo-boat HIYODORI, frigates OKI, AMAKUSA, MIKURA, FUKAE and kaibokan CD-2 and CD-3.

3 April 1944:
5 miles S of Tori-Shima. At about 1457, LtCdr (later Rear Admiral-Ret) Bafford E. Lewellen's (USNA ‘31) old USS POLLACK (SS-180) torpedoes and sinks TOSEI MARU carrying ammunition and rations at 30-14N, 139-45E. One passenger is KIA. The escorts counterattack USS POLLACK and drop 55 depth charges unsuccessfully.

8 April 1944:
N of Saipan. At 0228 (JST), LtCdr (later Vice Admiral) Frederick J. Harlfinger's (USNA ‘37) USS TRIGGER (SS-237) fires four torpedoes at the convoy, but fails to get any hits. While the troopships are diverted to the west, OKI and SAMIDARE counter-attack with depth-charges. Harlfinger runs at 300 feet or more for 17 hours as six escorts dog his trail and rain down numerous depth charges. Six DCs explode extremely close by.

When USS TRIGGER surfaces, her forward torpedo room is flooded to her deck plates, her hull air induction and most compartments are in about the same condition. The bow planes, trim pump, sound gear and both radars are all dead. Her radio antenna is grounded and USS TRIGGER cannot transmit. USS TRIGGER's crew spends the next four days making repairs.

9 April 1944:
62 miles WNW of Saipan. At 1625, LtCdr (later Captain) Slade D. Cutter's (USNA ‘35) USS SEAHORSE (SS-304) torpedoes and hits MIMASAKA MARU at 15-30N, 145-00E. MIMASAKA MARU is taken in tow by TOAN MARU. The escorts counterattack USS SEAHORSE unsuccessfully.

10 April 1944:
At about 0100 (JST), MIMASAKA MARU founders. She is carrying 1,146 Naval personnel, most all of whom are rescued and 1,437-tons of luggage. Seven naval troops, one soldier of the naval guard unit and ten sailors perish.

The convoy arrives at Saipan, then is split into separate groups that continue on to their respective destinations.

15 April 1944:
At 0400, CH-50 departs Saipan for Tokyo as part of the escort of convoy Higashi-Matsu No. 4 consisting of MAKASSAR, SHIRAMINE, TAKASAN, TOKO, KAKOGAWA, NISSHU and TAKAI MARUs and UNYO MARU No. 8. The other escorts include destroyer ASANAGI and torpedo-boat HIYODORI.

23 April 1944:
The convoy arrives at Tokyo.

29 May 1944:
At dawn, CH-50, CH-33, CH-17 and torpedo boat OTORI depart Tokyo escorting convoy No. 3530 consisting of TAKAOKA, SHINROKU, TAMAHIME, KASHIMASAN, HAVRE, SUGIYAMA, KATSUKAWA, KATORI MARUs and two other unidentified ships carrying troops of the 43rd Infantry Division.

4 June 1944:
At 1530, LtCdr (later KIA) Edward N. Blakely's (USNA ‘34) USS SHARK (SS-314) (later lost on patrol) torpedoes and sinks KATSUKAWA MARU at 19-45N, 138-15E. The transport is carrying 2,884 soldiers of the IJA's 43rd Infantry Division to bolster Saipan's defenses. 77 crewmen and 38 troops are KIA.

5 June 1944:
At 1645, Blakely torpedoes and sinks TAKAOKA MARU carrying about 3,500 reinforcments to the defenders of Saipan, at 18-40N, 140-35E. 25 crewmen and 115 soldiers are KIA. Immediately afterwards, Blakely torpedoes and sinks TAMAHIME MARU in the same position. 52 crewmen are KIA.

6 June 1944:
At 1000, LtCdr (later Admiral, CINCPACFLT) Bernard A. Clarey's (USNA ‘34) USS PINTADO (USS-387) torpedoes and sinks KASHIMASAN MARU with drummed aviation gasoline, weapons, ordnance and small craft for reinforcements to Saipan at 16-28N, 142-16E. 43 crewmen are KIA. At 1010, Clarey torpedoes and sinks HAVRE MARU carrying 2,816 troops in the same position. 91 crewmen and seven soldiers are KIA.

7 June 1944:
At about 2300, LtCdr (later Captain) James B. Grady's (USNA ’33) USS WHALE (SS-239) makes contact with the convoy traveling in two parallel columns: four freighters in the starboard column and two in the port. They are screened by three escorts. Grady makes a night surface radar attack on the largest ship, transport SUGIYAMA MARU. He fires a three-torpedo spread, then shifts to a second freighter and fires another three-torpedo spread. A hit under the stack of the first target at 31-06N, 142-34E is followed by two timed hits on the second target. Depth charges begin to drop immediately. USS WHALE clears the area to the SE. SUGIYAMA MARU escapes the area and is towed back to Yokosuka. Later that day, the remaining ships arrive at Saipan.

11 June 1944:
At 0400, CH-50 departs Saipan for Tokyo Bay with kaibokan CD-4 torpedo boat OTORI, subchasers CH-33 and CH-51, auxiliary subchasers CHa-20 and CHa-50 and TAKUNAN MARU No. 8 auxiliary minesweeper Wa-6 and auxiliary netlayer KOKKO MARU escorting convoy No. 4611 consisting of BATAVIA, HINKO, SHINTO (KAMISHIMA), IMIZU, NITCHO, REIKAI, TENRYUGAWA, KEIYO, BOKUYO (MUTSUYO), FUKOKU, MOJI, MAMIYA, INARI and TATSUTAKAWA MARUs and 16 other unidentified ships.

12 June 1944: American Operation “Forager” – The Invasion of Saipan::
Vice Admiral (later Admiral) Richmond K. Turner’s (USNA ’08) Task Force 52 lands Marine LtGen Holland M. Smith’s V Amphibious Corps and the invasion of Saipan begins. Vice Admiral (later Admiral) Marc A. Mitscher’s (USNA ’10) Task Force 58 launches aircraft from 15 carriers to attack airfields, defenses and shipping in the Marianas.

At 0935, that same day, at 17-32N, 144-10E, TG 58.4’s carriers USS ESSEX (CV-9), USS LANGLEY (CVL-27) and USS COWPENS (CVL- 25) find and decimate convoy No. 4611. They sink torpedo boat OTORI, and merchant ships KOKKO (two crewmen KIA), BATAVIA (59 crewmen and 18 passengers KIA), HINKO (nine crewmen and 12 passengers KIA including those KIA when sunk later in month by air attack), SHINTO (KAMISHIMA) (53 crewmen and 54 passengers KIA), IMIZU (67 crewmen KIA), NITCHO (14 crewmen KIA), REIKAI (40 crewmen and 42 passengers KIA), TENRYUGAWA (seven crewmen KIA), BOKUYO (45 crewmen KIA), FUKOKU (51 crewmen and 31 passengers KIA) and MOJI (53 crewmen and five gunners KIA) MARUs and damage TATSUTAKAWA MARU, CD-4, CH-33, CH-50 and CH-51, CHa-20 and Wa-6.

TATSUTAKAWA MARU is left drifting and finished off by gunfire three days later. 15 crewmen and two passengers are KIA. MAMIYA MARU is detached and sunk three days later near Iwo Jima with the loss of seven of her crew.

14 June 1944:
At 1310, USN codebreakers intercept and decrypt a message from the CO of CH-50 that reads: “Action Summary. 1. At 0935, 12 June, while escorting Convoy No. 4611 in position 17-32N, 144-00E, was attacked by formation of approximately 40 enemy carrier planes. -----. Planes withdrew at 1120. 2. At 1534 while convoy was still in process of reforming, was again attacked by approximately same composition enemy planes. Again we counter-attacked with everything we had, but suffered considerable damage, besides numerous dead and wounded. Commanding Officer seriously wounded. Planes withdrew at 1630. 3. ----- Casualties: 10 killed, 6 seriously wounded. 23 slightly wounded. Hull damage. Port side fuel oil tank hit below water line. Oil lost. Rice storeroom caught fire. Radar room flooded. Innumerable holes above waterline. Equipment damage: --.”

16 June 1944:
CH-50 arrives at Tateyama and departs later that day.

17 June 1944:
CH-50 arrives at Nagaura near Yokosuka.

19 June 1944:
Transfers from Nagaura to Yokosuka and remains there the remainder of the month under repairs.

9 July 1944: The Fall of Saipan:
Marine LtGen Holland M. Smith declares the island secure.

13 July 1944:
The repairs are completed. CH-50 departs Yokosuka and later that day arrives at Tateyama.

14 July 1944:
At 1440. CH-50 and CH-51 depart Tateyama for Iwo Jima escorting convoy No. 3714 consisting of NISSHU, HASSHO, KATSURAGAWA MARUs and UNKAI MARU No. 10. Other escorts are CD-4 and Navy Landing Ships No. 2 and No. 105.

18 July 1944:
200 miles NW of Chichi Jima. At about midnight, LtCdr Clyde B. Stevens’ (USNA ’30) USS PLAICE (SS-390) makes a surface radar attack on the convoy. About that same time, slow auxiliary gunboat UNKAI MARU No. 10, carrying aircraft spare parts, loses contact with the convoy.

NW of Chichi Jima. At about 0200 that same day, LtCdr Albert L. Becker‘s (USNA ’34) USS COBIA (SS-245) torpedoes and sinks straggler UNKAI MARU No. 10. 19 crewmen are KIA.

W of Chichi Jima. At 0650, Becker torpedoes and sinks NISSHU MARU that is carrying 1,500 troops including the 26th Tank Regiment and the 109th AA Unit, ammunition, guns and equipment for the defense of Iwo Jima. Three crewmen, 45 gunners and 48 troops including two tank crewmen are KIA and all 28 tanks lost. HASSHO and KATSURAGAWA MARUs and the escorts rescue almost 1,500 soldiers sailors and crewmen.

Tokyo. That same day, as a direct result of the fall of Saipan, Premier (and IJA General) Tojo Hideki and his entire war cabinet resign. This is a major turning point in the war because until then the military had essentially been in charge of the government.

19 July 1944:
The remainder of convoy No. 3714 arrives at Iwo-Jima. That same day, CH-50 departs the anchorage and patrols the local area.

20 July 1944:
CH-50 enters Futami Harbor, Chichi-Jima. USN carrier-based aircraft attack shipping in the harbor. At 1848, numerous bombs land in the water nearby. At 1850, a direct hit is received aft in the vicinity of her depth charge stowage compartment. At 1852, slow but steady flooding forces abandonment of the area. The ship begins sinking by the stern. A launch is lowered and the wounded are taken ashore. At 2200, attempts are begun to beach the vessel, meanwhile a single Diahatsu barge renders assistance.

21 July 1944:
In the morning, CH-50’s stern touches bottom. Still attempts are tried to control the flooding, but to no avail. During the early evening, the ship continues to settle. At 1840, Abandon Ship is ordered. At 1850, her bow goes under and CH-50 disappears completely from the surface. Casualties are 16 KIA and 10 wounded.

20 September 1944:
Removed from the Navy List.

Authors' Note:
Thanks go to John Whitman for info on CNO intercepts of Japanese messages. Thanks also go to Bill Somerville for info on CH-50's sinking and to Mr. Gilbert Casse of France.

-Bob Hackett, Sander Kingsepp and Peter Cundall.

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