Merchant ships
Desperate War of Japan in the Pacific
 Before the Pacific War
Tbl.8 Merchant ships [kGT] Hinkoku, p37
Japan4882,9964,317 5,630
US2,75015,99714,046 11,874
UK13,24218,33120,332 17,891
Germany2,6506724,199 4,483
France1,3503,2453,471 2,934
Japan grew martime shipping in WWI. Tbl.8 shows Merchant ships of Japan, US, UK, Germany and France. Japan had only 31.5% of UK in 1939. Japan built 2,242 GT of merchant ships from 1931 to 1941. Although Japan needed a lots of steel to continue war on China and prepare war for Russia since 1937, Japan decreased shipbuilding of freighters. How did Japanese leaders transport iron ore and coal from China to Japan? Japan also decreased shipbuilding of oil tankers to one forths in 1941 compared with 1939. If War broke out, a lot of merchant ships were necessary to transport troops in a campaign and to transport resources to product armaments. IJN needed a lots of tankers to refuel her fleet in order to intercept USN in the Pacific. IJN did not think of intercept USN far away Truk Atoll till 1941. Japan and German had to compete 2 big martime transport nations.

Tbl.12 Shipbuilding before the Pacific War [GT]
YearPassangerC & PCargoTankerSum
Japan had merchant ships 6.1 MGT for material ( cargo and tanker ) in 1940. IJN and civil bureaucrats thought that Japan needed 3.5 MGT to keep Japanese minimum life and maintain economic growth of 1940. IJA thought of 3 MGT. Actually IJA and IJN hired 3.71 MGT in December 1941. Only 1.71 MGT was for civil use. The civil peak was 2.86 MGT excluding oil tankers in October 1942. This meant that Japan could not transport iron ore and coal to product steel at once. Japan was dependent on 35% hired ships from US etc in 1941[7]. Japan ignored their martime transport powers. Japan had to build merchant ships at once if Japan prepared a war against both of US and UK. Nippon Yusen stopped Yokohama-Seattle line on 17 August 1941.[11]

 Simulation of merchant ships loss and building
Tbl.9 Estimation of Loss [kGT]
War yearLossBuilding
Japan built only 210,000t of merchant ships in 1941. It was minimum since 1935.

IJNGS estimated merchant ships loss in June 1941. Doi of IJNGS estimated that merchant ships loss would be 600-1,000 kGT in year, 600-800 kGT next year in the end of October 1941[5]. Some staff referred to real Atlantcic war between Germany and UK now. And navy ministry criticized that shipbuilding was optimistic because of warships repairs. Shipbuilding data was from Kikakuin[8].

Yoshida Zengo
Tbl.11 Building plan
Navy Minister Yoshida Zengo (1885-1966) remarked defense force for merchant ships in a board game war in May 1940. The game showed that it could not be enough to transport resources from French Indochina and Dutch Java, if Japan could occupy such territories. He said, "It would be nonsense to occupy Indo China without the sea lane defense.[6]" But he resigned on 15 September 1940. He had already had a meeting with Konoe, Tojo and Matsuoka at Konoe's Tekigai-so on 19 July.

A civil researcher of Total War Research Chamber estimated the loss using statics of Rolds registers in July 1941. The simulation and the war drill result showed that Japan could not war within 3 years because of stopping import. Japan would fail to lose transport power in four years. The institute showed the total war drill at Kantei on 27 and 28 August. But Army Minister Tojo told them not to express the result. I think that Tojo had decided to be War in August 1941.

Mail & Transport Ministry planned a shipbuilding in December 1941. I do not know why Mail & Transport Ministry made such a foolish plan (Tbl.11). Mail & Transport Ministry could not understand what to prepare in War, I think.

Ooi did not refer to whom estimated the loss, Other books writes, "Tomioka, a chief staff of department of GSIJN estimated merchant ships loss just before the Pacific War that Japan would lose 60 kGT per month." IJN had drilled that submarines attacked USN warship for a long time, though the drill showed it was ineffective. But I do not know why GSIJN thought USN also did not use their submarines for sinking merchant ships. In fact, USN CNO Stark ordered Asia submarine commander to action unlimted operation against Axis merchant ships in the south west direction of line 30°N122°E and 07°N140°E on 26 November 1941, if War broke between Japan[9].

Ithoh of GSIJN told that 360 destroyer escorts and 2,000 aircraft were necessary to decrease 30 kGT lost per month at a meeting in September 1943.

 The first lost merchant ship
IJA actioned landing operation on Malaya. 26 merchant ships transported troops of 50,000. The troops were equipped with 180 vessels, 135 tanks, 54 fort guns, 440 mountain & field guns, 2,500 heavy machine guns and 60,000 rifles. Awajiyama-maru was sunk by RAF aircraft on 8 December 1941, when IJA landed in Kotaabaru. This was beginning of the end.
Mountain gun
Battle of Malaya
Senin to yusousen no higeki
Singapore koubousen siryo
Malay oki kaisen

 Merchant ships loss
Tbl.2 Cause of Japanese loss
Bad weather281.1
Gun fire251.0
Tbl.3 Cause of Japanese loss
Carrier aircraft2.022
Land aircraft1.011
Surface warship0.33.3

Tbl.7 Allied loss
by IJN submarines

Tbl.1 Loss of nations Ouchi, p18
Japan lost her merchant ships as shown in Tbl.2 and Tbl.3 at the Pacific War. The ratio of bad weather and gun fire was almost the same. Airborne force and submarine became truely main sea powers from gunships in the Pacific. Merchant ships sent a lot of soldiers in the south of the Pacific. But IJA lost solidiers under the sea. They sank with IJA guns, ammunition, ration and equippment.

Actually the loss of cause of airborne attack exceeded in New Guinea, Truk, Philippines. The loss of cause of submarine decreased sharply because of no sea lanes in 1945. Tbl.7 shows that IJN submarines sank allied merchant ships in year. The sunk merchant ships decreased in 1943. This shows IJN operations did not run in the year.
Ouchi, p17, p52
Kimata, p314

Tbl.3 shows that carrier aircraft sank Japanese merchant ships twice as land based aircraft did. It seems USAAF were not effective to sink merchant ships. 77% of Japanese merchant ships were sunk by USN submarines and aircraft. IJN could not merit the London Naval Disarmament Treaty in the Pacific War, though UK and US admitted the same submarines GT to Japan. Navy work is to defend her own merchant ships, otherwise another navy work is to threaten an enemy sea commerce line, German navy did in WWI and WWII. Aircraft and submarine were the sea power in WWII.
Tokuda, p230

How much did other nations lose merchant ships? Tbl.1 shows the result. The US had lost 3 MGT for six months in 1942[1]. US decreased one tenth loss in 1943[2]. US won ASW (Anti Submarine Warware) against German U boats. I think the loss of US is little, though some people think US did not defend her merchant ships well.

 Transport and loss of merchant ships in year
Tbl.6 Transport and loss [kGT]
Fiscal yearTransportLoss
Japanese merchant ships transported 4.18 million GT monthly in December 1941. For military usage, the transport decreased 2.64 million GT in January 1942. The peak was 4.02 million GT in October 1942. The transport decreased shraply 3 million GT in August 1943, 1.99 million GT in June 1944, 0.74 million GT in June 1945. Tbl.6 shows transport by merchant ships in year. 7.71 million GT of 1945 was till Aug. It accounts only 24% of 1941 in year. Tbl.5 also shows loss of Japanese merchant ships in a fiscal year. 1941 and 1945 were 4 and 5 months each. The monthly average loss increased 1.5, 8.2, 14.8, 31 and 37 in year. I do not know how IJN thought USN submarine could not sink Japanese merchant ships in the Pacific, though German submarines had sunk UK merchant ships in the Atlantic. Allied lost merchant ships decreased in the Atlantic in 1943. Japanese lost merchant ships increased in the Pacific in 1944. These meant that Allied ASW did well in 1943 and IJN ASW failed in 1944.
Morimoto, p98-99
Oouchi, p16, p106
Hinkoku, p141
Tbl.10 Shipbuilding, capture and loss [GT] 1942 includes December in 1941
1942244,672609,211-36,000 817,8831,019,479-201,596
1943514,158102,831 -100,000516,9891,661,791 -1,114,802
19441,074,91329,565 -182,000922,4783,071,787 -2,149,309
1945473,9125,880 +318,000797,7921,175,810 -378,018
Tbl.11 Lost merchant ships of Allied nations in the Atlantic Ohuchi, p236

 Merchant ship crews in KIA
Tbl.4 Crews in KIA
Tbl.4 shows that Senbotu senin no hi kenritu-kai edited in March 1971. 60,331 crews of Japanese merchant ships were lost in KIA[3]. Foreigners were from China, Manchuria, Nanyo and Singapore. IJA and IJN servicemen of KIA ratio were 8% and 12% in the Pacific War. While merchant ship crews of KIA ratio was extremly high 46%[4]. To be sailors were safer than merchant ships crews ironically.

If War broke again, Japanese merchant ship would not run, I think. The crews are almost foreigners from Philippines and China etc. They will refuse to work on Japanese merchant ships. Japan has modernized 6 Aegis destroyers now. Are they useful to defend convoys from Persian Gulf to Japan? I find how important to cooperate with India and Thailand. The both nations have independent navy and aircraft carrier. Falklands Conflict showed how difficult to detect submarines even now.

 Wartime standard merchant ship
Merchant ship Kaizen Association of Japan recommended wartime standard ship of freighters till March 1939. The recommendation was added tankers and ore carriers in 1941. But the shipbuilding was not in time because of sunk loss. Japan shipbuilt more simplified 2nd wartime standard ship on July 1943. Japan shipbuilt 3.38 million gross ton of merchant ships in the Pacific War. Japan had 63 shipyards and 149 building berth in January 1945. 49 of 149 building berth were for IJN only. Japan estimated that 96 commerce building berth could shipbuild 2.50 million gross ton in a year. But it was impossible to shipbuild because of shortage of steel materials and skilled workers. Japan shipbuilt at peak in 1944, while US is in 1943[10]. Although Japan began the Pacific War, Japan was late to shipbuild merchant ships. Japanese Government's v policy failed. Originally Japanese merchant ships were short. Running efficency got worse because of a few US submarines. Japan had to prepare a lot of kaibou-kan ( corvette ) at first. IJN established a kokutai for ASW on 15 December 1943.

While US Congress passed Merchant Marine Act in 1936. The United States Maritime Commission (USMC) was established. USMC planned standard shipbuilding of merchant ships. FDR announced shipbuilding of 200 ships(1.4 million GT) on 31 December 1941. US government announced one shipbuilding plan after another as follows,

    1941Apr Plan #2 112 merchant ships
    1941Jul Plan #3 418 merchant ships
    1941Oct Plan #4 632 merchant ships

US Government announced shipbuilding of 1,362 ships (9.77 million GT) in 1941 totally. 765 (5.49 million GT) ships of 1,362 were completed in 1942! While Japan shipbuilt 0.61 million GT the same year. It was one ninth of the US only. US also began to build 159 new building berth and worked them in 1943. Finally US built 2,580 liberty ships size of 7,180 GT, totally 18.5 million GT. In case of oil tankers, the standards were T-1, T-2 and T-3. Seven shipyards built 113 T-1s. US delivered 533 T-2 tankers. The first 12 T-3 tankers were the first ships bought by the U.S. Maritime Commission, before settling in to the longer-term T2 program. The remaining 51 were built later. How did Japanese leaders think of the US wartime merchant shipbuilding announcements?
Ouchi, p80-82, p96, p273
Senji, p161-163, p171, p173
T-1 tankers
T-2 tankers
T-3 tankers

 Merchant ship site tips in Japanese
  • Senbotsu sita Fune to Kaiin no Shiryou-kan shows some photos of sank merchant ships in the site.
  • Senbotu-sen wo kiroku suru Kai shows annual distribution of lost ships in parts of the Pacific
  • Iwojima tanpou writes lost merchant ships around Iwojima
  • Tenshou kantai writes a story of IJN transport ships used for hunting whales in hunger of protein after the war.

    [1] NHK1, p94
    [2] NHK1, p102
    [3] Honsekitibetu
    [4] Morimoto, p137
    [5] NHK1, p39-41
    [6] Morimoto p.107
    [7] NHK1, p126
    [8] Gunzo, p35, No59
    [9] NHK1, p70-71
    [10] Kansen seizou-ryou ni miru nichibei-sa
    [11] Seattle line

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