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Nevertheless, large convoys started to be organised, under the command of experienced
officers. The Japanese were also able to use direction-finding techniques to locate
submarines, although they lacked a communications system that could rapidly disseminate the
information. 52 Even as the Escort Command was expanded, the shortage of such basic items
as sonar and depth charges remained serious. 53 Late in the war, magnetic anomaly detectors
were introduced but these were provided in too small a quantity and too late in the war to
make an impact.
As the US Navy’s post-war Strategic Bombing Survey noted, Japan’s lack of technical
sophistication in anti-submarine operations, its lack of focus on convoy operations for the
first two years of the war, and its lack of a centralised system for information about submarines
and other hazards, made merchant vessels easy prey for US submarines. 54 More importantly,
Japan’s lack of a coordinated anti-submarine capability for two years provided the US submarine
force with two years to learn, adapt and become highly proficient at commerce raiding, in an
environment where they faced a threat much less capable than pre-war estimates.
The state of the submarine campaign – 1944
In 1944, the US submarine campaign broke the back of the Japanese merchant fleet. By
September that year, there was a near complete blockade of Japan. The Japanese had lost so
many merchant vessels that sustaining the war economy was becoming impossible. 55 Wolf
pack tactics, night attacks on the surface and aggressive execution of attacks were all elements
of submarine operations that had emerged based on wartime experience. With more of the
new Gato and Balao class submarines, improved technology such as radar, smaller patrol areas
as the Japanese retreated, and targeting Japanese shipping through signals intelligence, the
submarine force was now operating at peak performance.
Post-war analysis confirmed that 603 Japanese ships were sunk by submarines in 1944,
exceeding the combined total for 1941 to 1943 (see Figure 4). 56 Japanese ships were hampered
by fuel shortages and forced to sail slowly, or follow direct routes instead of evasive ones.
Japanese military pilots could not be trained because of a lack of fuel. 57 The year was also the
most successful one for US submarine attacks on Japanese surface combatants, sinking one
battleship 58 , seven aircraft carriers 59 , nine cruisers and 30 destroyers. 60
Gross Tons
5,000,000
4,500,000
4,000,000
3,500,000
3,000,000
2,500,000
2,000,000
1,500,000
1,000,000
500,000
0
1941-1942 1943 1944 1945* Totals
GROSS TONNAGE OF SHIPPING SUNK BY —
OTHER CAUSES
Submarines Army air Navy and marine air Laid mines Miscellaneous mines, surface gunfire, shipwreck, etc
The destruction of the Japanese merchant marine by various attacking agents (ships over 500 gross tons only)
* Figures for 1945 include ships damaged and put out of action for the duration
Figure 4. Japanese merchant marine losses by cause and year 61
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