Desperate War of Japan in the Pacific
 Fuel consumption rate
Fuel rate of Asashio class destroyer
Speed [kt] 10151824283034
2nd Range [nm] 5,7004,6234,0002,8042,0441,675 960
3rd Range [nm] 5,7004,3643,5122,1481,5401,310 960
2nd Fuel [nm/t]
3rd Fuel [nm/t]11.48.774.
IJN task force ( kido butai ) accomanied 9 destroyers in Pearl Habor operaion, which left Hitokkapu Bay on 23 November 1941. 7 of 9 destroyers were Kagero class. And the rest were Asashio class[2]. Range of Kagero class was 5,000 nm at 18 kt, otherwise Asashio class was 5,700 nm at 10 kt, 960 nm at 34kt[1]. The displacement of Asashio class was less than 120t compared with Kagero class. As fuel capcity of Asashio class was 500 t, I guess fuel capacity of Kagero class was 620 t. So, Kagero class spent fuel of rate 8.1 nm/t at 18kt.

Drag force is proportional to speed by Newton's law. The drag force is proportional to square of speed considering area effect of the body. I computed fuel comsumption rate of Asashio by 2nd order (square) interpolating function. Considering the work of engine, drag force D is,

    D = kv²
    Dds = kv²ds ( ds is infinitive length )
    dW = Dds
    dW/dt = kv²ds/dt ( dt is infinitive time )
    P = kv³ (dW/dt = P, ds/dt = v)
Power is proportional to cubic of speed. Pitch of propellar is not variable. Power is dependent on revolution of propellar. Fuel consumption may be proportional to the revolution of engine. Capacity of fuel is constant. So range is inverse proportional to cubic of speed. Interporation curve of range is a function of
    Range = k/(v³-h)
The result is as follows. Asashio class may run 4,000 nm at 18kt judging from the fuel capacity. This is shorter than 1,000 nm than Kagero. How much fuel did the destoryers spend? After refuel off 600 nm Hawaii, The KB ran. The KB stayed till 13:00 to receive aircraft[5]. Sunrise and sunset are 6:56 and 17:49 in Honolulu on 7 December[7]. The KB ordered to launch aircraft at 6:00.
    24 kt for 5 hours 120 nm 21 t
    28 kt for 5 hours 140 nm 34 t ( Kaga's max speed )
    ? 110 nm 14 t ( in case of 18 kt )
    26 kt for 5 hours 130 nm
    20 kt for 6 hours 120 nm
It looks very little. The KB might run zigzag. The destroyers always have to adjust output of engine to keep formation of the KB. In fact, some destoryers refueld 200 t in 30 hours depearture from Hitokkapu Bay[3]. The KB ran at 14 kt. The destroyers was to spend at the rate of 2.1 nm/t at 14 kt. 7 Oilers fueld destoryers on 28, 29, 30 November, 1, 2, 5, 6 and 7 December. I do not know how each destroyer refueld. The destroyers was short of fuel, if the incredable rate was true.

Light cruiser Abukuma refueld on 30 November, 1, 2, 5, 6 and 7 December. Why did Abukuma refuel with capacity of 1,260 t seven times in spite of 5,000 nm range at 14 kt? IJN range data of warships were planned values. The displacement of Abukuma increased 1,500 t comparing with the original 5,500 t[4]. The range might decrease 27 % at least. After all, speed of the KB was limited by aircraft carrier Kaga, and freedom of the operation was limited by the fuel capacity of Kagero class destroyers.

 Escort carriers
IJN destroyers ratio per carrier
OperaionFleetCarriers DestroyersRatio
PearlKB69 (7) 1.5
Mariana1Sf313 4.3
Ref. Genda p.274
Only 9 destroyers had escorted 6 aircraft carriers in Pearl Harbor Operation. Two destroyeres Kasumi and Arare were seperated from KB to escort oilers. The both were Asashio class destroyers.

Though 2 battle cruisers, 2 heavy cruisers and 1 light cruiser also escorted, they had no depth charges for ASW. IJN thought that USN submarines were not threat because of unknown operation, didn't it? The table shows ratio of destroyers per carrier. Some historians criticizes that the KB should do the third air strike. Could only 7 destroyers shield 6 aircraft carriers effective?
USN destroyers ratio per carrier
OperaionFleetCarriers DestroyersRatio
OkinawaTG58-1521 4.2
TG58-238 2.7
Ref. Yomitan history, ASW

 The biter is sometimes bit
CNO King of USN ordered submarines to sink destroyers than merchant ships at first on Apr 1944. IJN lost 11 destroyers, 4 destroyer escorts and 3 other escorts because of enemy submarines from April to Jun 15th.

IJN selected Tawi-tawi as anchorage port of 1st Kido Fleet. Saipan is nearer to Japan than Taui. The reasons were,

  • Gunreibu guessed USN would invade Palau at first
  • Shortage of oilers was to anchor near oil export

But Tawi-tawi was enroute that USN submarines ran from Freemantle to the South China Sea. And worse Tawi-tawi and Japan was the same distance from Kwajalein.

1st Kido Fleet came to Tawi-tawi on May 13th. It was necessary for pilots of carriers to train landing everyday etc. Carriers could not run to train pilots out of the port freely, becasue submarines were hiding. So 1st fleet ordered destroyers to sweep submarines. 4 destroyer were sunk one by one for 4 days. These were Minazuki, Hayanami, Kazakumo and Tanikaze. Ooi p.238-241

Sonars of the destroyers were worse than US submarines. I do not know how each destroyer repeated failure of anti submarine combat. The below is image of the Tawi-tawi Bay

 Depth charge
The table shows 3 types of discharges which IJN developed in 1937 to 1943.
Specifications of IJN depth charges
TypeYearDecending speedSet of Depth [m]ExplosiveWeightLengthDiameter
Type 9519371.9m/s30, 60100kg160kg775mm450mm
Type 219422.0m/s30, 60, 90, 120, 150100kg162kg775mm450mm
Type 319435.0m/s40, 80, 120, 160, 200100kg180kg1400mm450mm

The production of depth charges was as follows. Strangely production of 1943 decreased. Was production of Type 3 depth charge in 1944 actually?
Production of IJN Depth charges
Sekai no kansen, No.507
Gunzo, p5-11, No74
Bakurai ichiran
Goei heiki

3 US destroyers were sunk by a storm off the west of Philippines on December 18th 1944. The above diagram shows a loci of the fleet TF38. The loci is a flag warship, USS New Jersey.
Weather, p
Typhoon Cobra(1944)

RN took a note to shipbuild small warships for ASW on February 7th 1939. RN orderd development of a modified catcher boat on 24th. The first ship was launched on April 6th 1940. After all, UK and Canada shipbuilt 143 and 122 each. The diagram shows the layout of the Flower class. A sonar called ASDIC 123 equipped at first. The ASDIC was installed in a section shown encircled number 6. While destroyer escorts of IJN were not equipped with a sonar in the Pacific War.
Gunzo, p22-27 No94

[1] Jentschura p.147
[2] Koei p.20
[3] Sensou to sekiyu (4)
Nagara gata no kindaika
[5] Shinjyu-wan kougeki
[6] Sekai no hinode-hinoiri

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