ASW (Anti Submarine Warfare)
Desperate War of Japan in the Pacific
This page contains kanji characters.

IJN dispatched a tokumu kantai to the Mediterranean Sea in WWI. Flag ship of the fleet was Cruiser Izumo. The fleet consited of 3 squadrons.

    10th SQ : Kaba class destroyer Katura, Kaede, Ume and Kusunoki
    11th SQ : Kaba class destroyer Sakaki, Kashiwa, Matsu and Sugi
    15th SQ : Momo class destroyer Momo, Kashi, Hinoki, Yanagi
After WWI, an officer named Niimi Masaichi ( ) studied ASW in UK for a year in 1922. He offered his report CNO of IJN. The CNO Yamashita Gentaro (Ϻ) wrote a remark such the sea of regret would not come true.[14] Yamashita became CNO on 1 December 1920 and had been till 15 April 1925. Later Niimi had been a vice admiral for three years. He was the same class of Naval Academy of Shimizu (6F commander), Sawamoto (Deputy Navy Minister) and famous Nagumo. But IJN did not study ASW but was sleeping deep. Sawamoto was a typical military bureaucrat. I think that he advocated and decided to break at war in December 1941. He became one of two admirals in the end of the Pacific War.

Tbl.3 Allied forces interwar period

UK China StationUS Asia Fleet
Gun boat-11
Aircraft carrier1-
TroopInfantry 2,300Marines 1,200
Tbl.3 shows forces of UK and US in Far East in interwar period. USN and RN thought that submarines was sea power in the Pacific before WWII. USN submarines became main sea power in the Pacific War, though RN could not use the power effective in WWII. Both IJN and USN increased loss of submarines each other in 1944, as I show the comparative loss of IJN and USN. Especially IJN destroyer escorts actioned much in 1945, though it was too late to compete USN. This was an origin of Martime self defense force of Japan now.

IJN sank 51 allied navies submarines. But A lot of Japanese merchant ship were sunk by US submarines. Japan lost 5.3 million GT of merchant ships by allied submarines. While allied navies sank 97 IJN submarines, and allied nations lost 1.4 million GT of merchant ships by IJN submarines. Japan's merchant loss increased year and year. But allied merchant loss decreased. USN submarines sank 603 Japanese merchant ships in 1944, while IJN submarines sank 28 allied merchant ships only. Why did IJN fail in ASW? USN and IJN had prepared fleet submarines before the Pacific War, though both navies knew British ASW in WWI. But USN changed them for destroying commerce lines at the War, though they were troubled by bad torpedos. While IJN used for reconnaissance and sinking main warships. IJN had found that submarines could not attack a fleet in a drill. IJN did not change how to use submarines. USN admitted how to use submarines and ASW in 1942 at once. But IJN could not evaluate commerce line crisis as USN did. I think US commons always checked USN performance. The US people did not allow their merchant oil tankers were sunk by U boats. Otherwise Japanese people always endured various feed tickes, and were subjected to Government. Tojo sometimes said, "We must endure and continue to fight." But IJN did not obey Tojo Government demand to defend merchant ships. IJN was too proud and stupid to fight ASW against US submarines. I was sad to read how IJN admirals commented on US submarines just after the Pacific War. As matter of fact, GF (Grand Fleet) could not defend themselves well. 4 destroyers were sunk one by one for 4 days in the Tawi-tawi Bay in June 1944. So aviators did not train themselves on aircraft carriers because the carriers could not run in the bay before the Mariana Battle.

Tbl.1 Cause of IJN submarines loss
Kimata, p301
CauseType IType RoSum
Destroyer escort11920
Depth charge Mk9
US merchant ships ran showing navigation light at night, and informed their locations by wireless signals. USN informed escort warships schedule and aircraft patrol by wireless signals. U boats heard these signals.

King directed ASW himself. He ordered that a merchant ship did not run alone and ran by a convoy in August 1942. USN built 200 destroyer escorts for eight months in 1942. USN established 10th fleet in spring 1943. USN and RN could break wireless signals of U boats. USN pressed U boats by aircraft and hunter-killer tactics. At last U boat retreated from the east coat of the US and the Caribbean Sea in May 1943[1]. USN destroyers escort were equipped with a surface PPI radar.

USN used Mk 6 depth charge which decent at 2.5m/s. New Mk 9 was 6m/s decending speed in Mar 1943. In fact, loss of IJN submarines increased after Q2 of 1943, as shown in Tbl-103.

USN had a lot of destroyer escorts. Pairs of hunter and killer searched and destroyed IJN submarines in 1944. Hedgehog could attack a submerged submarine within 180m forward. The hedgehog sank at fast speed of 6.7 to 7.2 m/s. Ro-501 was sunk by the hedgehog in May 1944 for the first time. The hedgehogs sank Ro-105, -104, -116, -108, -105, I-10, -37, -46, -48, -54, -177, -182, -363 and -370. Mouse trap was a rocketed hedgehog. The mouse trap sank I-32 in Mar 1944[2]. USS Anzio (CVE-57) sank I-367 near Iwojima, using a homing torpedo Mk.24 called FIDO which was released by aircraft. Tbl.1 shows causes of IJN submarines loss. The loss by aircraft was far fewer than submarines. The total number 90 is not the same as Hashimoto showed 97 already.

 Okinawa battle
Submarine I-58 of IJN could not advance well at night in Okinawa Battle because of an enemy aircraft at night, though a warning radar of I-58 also could detect it well. I-58 carried 5 manned torpedos called Kaiten. I-58 tried to go the west off shore of Okinawa twice. They were from Apr 5th to 9th and from 11th to 14th. I-58 had not observe stars for navigation once. The longest floating time was 3h53m. The shortest floating time were 1h10m only twice in the nearest position of Okinawa. I-8, Ro-46 and Ro-41 went to the south of Okinawa. They were lost. I-47, I-56, I-58 and I-44 formed sucide attackers carrying Kaitens. I-47 came back on the way because damaged by depth charges. I-56 left on Mar 31st and was sunk by destroyer in the west of Okinawa. I-44 left on 3 April and was sunk by destroyer on 18 April in the east of Okinawa.
Hashimoto, p289-290, p294-295

USN used sea planes well which were useful for patroling at night, and had a carrier force group in Okinawa then. Avengers of TG52 patroled and searched submarines daytime maybe. 6 TBM-3Es patroled at night.

 Japan's loss vs USN submarines
Tbl.2 Japan's loss vs USN submarines Tokuda, p231
YearIJN warships
kton (number)
Japanese merchant ships
kton (number)
US submarines
Sorties (loss)
1941-4211.0 (2)725 (180.0)350 (7)
194329.1 (22)1,500 (335.0)350 (15)
1944405.7 (104)2,700 (603.0)520 (19)
194566.1 (60)415 (186.5)330 (8)
Tbl.2 shows USN submarines kills at the Pacific. USN increased sorties of 58% in 1944. The submarine loss also increased 27%. While Japan lost 14 folds of warships and the loss of merchant loss increased 80% in 1944. IJN warships could not defend themselves from USN submarine attacks well. USN submarines increased the kill ratio 5.4 from 1.5 against IJN warships in 1944. Lost allied submarines are also shown in the table of quarterly changes in the Pacific. Tbl-102 shows how IJN submarines sank except for combats.

IJN did not have serious concern about defense of merchant ships because of disorder of US Mark 14 torpedos. USN submarines were equipped with a surface PPI SJ radar in the end of 1942. And USN broke cipher of Japanese merchant communication signal which was called maru code by USN in the beginning of 1943[8]. USN adopted Torpex explosive as warheads of torpedos in February 1943. USN Lockwood ordered his boats to deactivate the Mark VI magnetic influence exploder and use only its contact pistol in July[7]. Soon US submarines began to damage to Japanese convoys heavily.

IJN renamed Mine School as Anti Sub School on 25 March 1944, though Training was conventional to listen a tune and how to handle passive and active sonars for young sailors.[12] It was too late to train anti sub crews.

Martime Escort Headquater () found USN adopted wolfpack tactics, because IJN warships listened to VHF telephone talk among USN submarines[4], when IJN aircraft carrier Chuyo was sunk on 4 December 1943. IJN Headquater agreed to use mines at last. The mines were begun to install in the west of Kyushu in Feburary 1944. Martime Escort HQ was to use 4 auxiliary aircraft carriers, but they had to repair for half a year[3]. Destroyer escorts ran at a loss unequipped with a surface radar on 18 August 1944, when IJN aircraft carrier Taiyo was sunk[5]. When auxiliary aircraft carrier Shinyo was sunk on 17 November 1944, a few destroyer escorts were equipped with a surface radar. But the using skill of the radar was poor, Oui wrote[6]. I think it was difficult to find and distinguish the enemy in the convoy because the IJN surface radar was no PPI.
      Arisawa of Escort HQ planned to deploy landed radars in the islands of Luzon Strait[9]. But merchant ships could not pass the strait any more, when the radar was deployed.

 IJN air patrol 901st group (Kokutai) for ASW
901st Kokutai was a specillized anti submarine patrol aircraft group equipped with air borne radars and magnetic submerged submarine detectors KMX in 1944. It had probably result that 901st Kokutai might sink 5 US submarines in October 1944.[13] The detector is called MAD ( Magnetic Anomaly Detector ) now. But GF used the old slow speed aircraft in the battle against US fast carriers task forces, and Escort Headquarter lost almost of the aircraft.

IJN 901st Kokutai HQ
1944Jan dispatched 6 Nells to Okinawa (Oroku)
1944Aug30from Tateyama to Okinawa
1945May15from Okinawa to Korea(Jinhae-si)
IJN could develope magnetic anti submarine detector in the end of the Pacific War at last. A kokutai was established for ASW at first on 10 December 1943 in Tateyama, which was named 901st kokutai. IJN had not studied air tactics of ASW yet at all. A commander of the 901st kokutai had to begin nothing. Goei shireibu did not give time enough to train, and ordered advance to Okinawa on the mid of Jan 1944. The aircraft were 24 Nells and 12 Mavis. 901th kokutai had damaged heavily by raids through Oct 12 to Oct 26 1944. A Nell could detect a submarine by radar in July 1944.

Magnetic detector KMX
Revolutionary magnetic detectors were in practical use on Aug 1944. IJN developed a submarine detector called KMX like a MAD in November 1943. It could detect a 3,000t submarine over 160m width 120 m. In case of a 1,000t submarine, it decreased over 120m width 90m. The detecting signal was very low alternative. IJN adopted frequency multiplier that Sony founder Ibuka devised.

IJN planned new anti submarine aircraft named Tokai to product compared very small to Liberator, and might be cheap. KMX were supplied with them. IJN tried to product more than 1,000 Lorna ( Toukai ), but it was too late.
Ibuka Masaru(1908-1997)

    MAD of JMSDF is AQS-81 detecting at 500 - 1,000m now. Aircraft detect only 500m width under water submarine even now. A Chinese submarine poped up just aft a US aircraft carrier near Japan.

Carrier aircraft
901st kokutai was used to search a fleet in October 1944 near Taiwan, because Nell of 901st kokutai were equipped with airborne radars. They were lost. USN carrier aircraft raided in airfields on the west coast of Luzon. Aircraft with KMX were lost by the air raid.
Oui, p305-307

 USN Catalina ( PBY ) with MAD
A US Catalina squadron arrived to patrol with MAD ( Magnetic Anomaly Detector) at Port Lyautey in January 1944.[21][22][23] Peillard wrote that MAD was Magnetic Air Detector and a pair of PBYs flew at the height of 45 or 60 mi. The mad could detect a U-boat at depth of 60 m. I think that the translation of height was wrong. It might not be mile but meter.

Germany had tried dispatching 95 U-boats at the Mediterranean since September 1941. 12 U-boats gave up. 5 U-boats were sunk on the way to the south. 78 U-boats could arrive at the mouth of the Strait. 6 of 78 were sunk and anthor 6 of 78 were damaged. 62 U-boats could enter into the Mediterranean. There were 26 U-boats in the Mediterranean.

 Submarines killed enemy submarines
Enemy submarines sank IJN submarines twice compared with aircraft as shown in Tbl.1 I-25 sank an unknown submarine off Oregon State 600nm on 12 October 1942 which was a Russian submarine, L16. I-122 was torpedoed in the Japan Sea on 10 June 1944. Therefore IJN had few surface areas to train submarines in safety[11]. US and UK submarines sank 14 and 3 IJN submarines each, otherwise Yamaguchi, a captain of IJN I-176 only sank USS Corvina (SS-226) on 17 November 1943[10]. Didn't SJ radar of Corvina work at the night? I-176 ran north for Truk at 16kt on 16 November. I-176 had a damage by depth charges. She was to repair in Japan mainland.
    2212 spotted at Northeast, range 8,000m
    2218 submerging
    2357 range 2,500m, unavilable attack angle, 2hr later Corvina changed the direction
    0020 fires 3 torpedos
    0021 2 torpedos hit
    0030 I-176 afloat

[1] NHK1, p99-103
[2] Kimata, p300-306
[3] Oui, p165-166
[4] Oui, p211
[5] Oui, p291-292
[6] Oui, p322
[7] Sensuikan Kohgeki, p93
[8] NHK1, p163-164
[9] Oui, p163
[10] Sensuikan Kohgeki, p87-88/ Kimata, p190
[11] Hashimoto, p305
[12] Sensuikan kougeki, p120
[13] Oui, p301-302
[14] NHK1, p68-70
[21] Peillard, ge, p182-183
[22] Consolidated PBY Catalina
[23] History of Port Lyautey

 IJN sonar
Type 93 sonars on surface vessel Ouchi, p112-113
Passive10deg at 12kt
3deg at 12kt
- at 8kt
- at 6kt
Active2deg at 12kt
+/-200m at 12kt
Max 2,000m
Min 300m

Type 93 model 3 Kansen, No320
Max range1,300m at 12kt
1,000m at 14kt
Min range500m

Type 93 passive sonar in 1937
Target speedRange
3kt1,700m at 1.5kt
1,000m at 4kt
4kt2,800m at 1.5kt
2,300m at 4kt
5kt3,000m at 1.5kt
2,300m at 4kt

Type 3 sonar specifications
Frequency13, 16kHz(alternate)
Max range2,000m at 12kt
1,200m at 14kt
Min range150m

Type S active sonar
on U-boat
Hirota, p442-443
Frequency15 kHz
Power5 kW
Pulse20 ms
Accuracy±2° at 4,000 m
Sonars were equipped with destroyer escorts in fall 1942, though IJN had developed passive and acitve sonar in 1933. Its detector was dynamic microphone. There was an argument that IJN should adopt crystal type detector or not in the beginning of the Pacific War.[3] The table shows both specifications. Passive type was called type 93 passive sonar ( 93 shiki choonki). Active type was called type 93 active sonar ( 93 shiki tanshingi ). The active sonar could hardly detect a target inner range 300 m. Detectors of type 93 passive were 16 dynamic microphones on the pherial of diameter 3 m.

I suppose that it was impossible to measure distance of a target in case of type 93 passive sonar. Another data of type 93 might be in fact. It shows that dead distance was 500 m. I find how allied hunter killer tactics was effective considering the dead distance.

Destroyer Kagero got a range 3,200 m at 8 kt, 1,000 m at 14 kt applying for type 93 passive sonar. Destroyer Hatsuzuki got a range 5,000 m at 6 kt, 2,600 m at 12 kt and 2,000 m at 14 kt.[4] There is another data of passive sonar tested in submarine school in 1933.[7]

IJN dispatched military delegation to Germany in 1941. IJN was trying to copy French SCAM then. IJN found active sonar important. IJN Laboratory began to develop the new active type sonar with NEC in 1941. NEC made 30 to 50 sonars at month in 1943.[1] This type was called type 3 ( 3 shiki tanshingi ). Transducer of the original German type was crystal. So 2 German sound engineers came to japan on a German cruiser in 1943. One was an expert of production of the crystal. Toshiba was to product the crystal, but the factory was destroyed before production by B-29 air raid in 1945.[2]

According to Hirota, U-boats adopted Type S active sonar. But German submariners hardly used active sonar.[5] An IJN engineer proposed a new way how to detect a surface ship. It was to equip detectors at bow and stern of a submarine. IJN did not approve it at first. Its method looked like German GHG which had 24 detectors, I suppose. In the end of the Pacific War, there were a lot of stock of the new type sonars, though IJN had not have enough submarines suitable for them any more.[3]

Sonars of RN destroyer escorts had range of 1,100m to 1,400m in the Atlantic Battle.[6]

It was necessary like hedgehog or squid to attack forward for IJN. Or a pair of a hunter detecting a submarine and a killer attacking it was the best way like DE-635 England. But it was to too late to shipbuild a lot of kaibou kan. Kaibou kan was smaller than corvette. After all Japan lost a lot of merchant ships and crews' and soldiers' lives aboard.

 Wireless signal locator
RN suceeded in positioning a U-boat from a short transmitting wireless signal in 1939. The principle was a simple goniometer.
Rengogun, p124-125
HF/DF An Allied Weapon against German U-boats 1939-1945
FH4 DF System

Captains of IJN warships said, 'I heard US submarines talked each other.' If IJN also invented the same device, loss of merchant ships would decrease. I suppose taht Huff Duff was just a complicated Kurtz direction detector for aircraft. IJN warships had not been equipped with such a huff duff. But radio stations detected directions of enemy warships. one or two IJN aircraft flew to the surface of a US subamrine soon, when the submarine emitted a message to report offshore Japan in 1943.[8]

Kansen, No217
[1] Nakagawa, p188-189
[2] Toshiba
[3] Nakagawa, p193-194
[4] Chouon-ki
[5] Hirota, p442
[6] Peillard, ge, p333
[7] Gunzo, type 13 submarine chaser p13, No51
[8] Enright, p227

© 2008-2011 Enoki Sensor All Rights Reserved