If you’re familiar with World War 2, the chances are you’re familiar with
the Battle of the Atlantic- Germany’s attempts to suffocate the Allied war
effort with U-boat submarines attacking merchant shipping.
It was one of the key battles of the war, but it wasn’t the most successful submarine campaign.
On the other side of the world in the pacific, the American Navy was in its own little-known battle
against Japanese merchant shipping, that would prove to be utterly devastating to the Imperial
war effort. -
In the years leading up to 1941, the US navy did not intend for submarines to form the backbone
of a war against Japanese merchant shipping. In fact, in 1930 the US had joined with Britain in
calling for submarines to be banned under the 1st London Naval treaty. This proposal never made it
into international law, but American disdain for using submarines to attack civilian shipping was
real and was a long way from the US navy’s thoughts in the 1930s.
That’s not to say they didn’t plan on using submarines though.
As the prospect of war with Japan came into focus, construction of submarines was stepped up. But the
new American boats like the Gato and Balao classes weren’t designed for attacking merchant ships
necessarily. Designated as ‘fleet’ submarines these boats were more than twice the size of their
German counterparts, designed to carry a larger number of torpedoes and operate at greater range
in order to attack enemy warships. Both the US and British navies did
plan to interdict Japanese shipping and blockade the home islands, but
with surface ships operating from forward bases at Hong Kong and Manila, not with submarines.
But on December 7th 1941, there was a change of plan. Just four hours after
Japan attacked Pearl Harbour, Admiral Harold Stark, Chief of Naval Operations,
ordered the U.S Navy to “execute unrestricted air and submarine warfare against Japan.”
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Japan’s war economy in 1941 was incredibly vulnerable to the disruption of its shipping.
Even before the offensives to Malaya, the Phillippines and the Dutch East Indies began,
Japan’s merchant fleet was already burdened with carrying troops and supplies to and from China.
After almost all of South East Asia had fallen to Japan it had access to all the raw materials it
could ever need, but the iron ore, bauxite, rubber and oil still needed to be transported back to
Japan to be useful. Troops, aircraft, ammunition and weapons had to flow in the other direction
to defend what it had taken. And a huge amount of shipping had to flow through a single area
between China and the Phillippines. Cut this route off, and you might be able to
strangle Japan’s war economy into submission. That’s the theory, but in 1942 it was a distant
prospect and did not rank as the US Navy’s top priority. Pacific submarines, under Rear
Admirals Thomas Withers and then Robert English, were given a wide variety of tasks in support of
surface forces. Boats were sent to lay mines, conduct reconnaissance, collect weather data
and deliver supplies to beleaguered land positions amongst other things. A lot of patrol time was
also given over to attempting to intercept and sink Japanese warships. These attacks were rarely
successful- warships were fast and hard for a submarine to catch and engage. Of 23 contacts with
Japanese capital ships in 1942, only 4 resulted in damage to enemy ships with none sunk. In
fact Japan’s submarines did a better job on this front- they managed to sink the carriers Yorktown
and Wasp and heavily damage the battleship North Carolina and aircraft carrier Saratoga.
When not tasked to other activities, American submarines carried out good old-fashioned commerce
raiding across the western pacific, sinking in 1942 274 merchant ships. Or at least, that’s what
was claimed at the time. In the heat of battle the size of ships could easily be inflated along with
the number sunk. A post war report by the Joint Army-Navy Assessment Committee in 1947 put the
figure at 154 merchant ships sunk by submarines in 1942. Aircraft, mines and other losses accounted
for another 87 ships. Either way it was not a strong performance, especially when compared to
German U-boats, which in the first half of 1942 alone had sunk 526 allied ships in the Atlantic.
The reasons for this underperformance were varied, and not unconnected to the loss of submarine bases
at the Phillippines and Guam as part of a year in which the US was in retreat. Problems specific to
the submarine service ran deeper than that however, starting with their equipment.
The standard weapon for American submarines was the mark 14 torpedo, which had been developed
in the 1920s and was untested in combat in 1941. Almost as soon as the war began,
doubts began to emerge over its reliability, with numerous boats reporting that it failed to explode
correctly. As an example, shortly before Christmas 1941 the USS Sargo fired eight torpedoes at four
different targets and got no hits. Suspecting something was wrong, the boats skipper,
Lieutenant Commander Tyrrell Dwight Jacobs, then spent almost an hour precisely tracking a new
target on December 26th. Every measurement was double and triple checked and the boat closed to
within 1,000 yards of the target before firing four torpedoes. All of them failed to explode.
Now, mark 14 torpedoes had two methods of detonation- by contact with a ship,
or a magnetic detonator which would be triggered as the torpedo passed underneath. It would later
emerge that both were defective- though the navy was slow to acknowledge it and even slower to
fix it. By the time 1942 ended no live tests of the torpedo had taken place, and the subs
would enter 1943 with temperamental torpedoes. The American submarine fleet also experienced
problems with its officers, both sub captains that weren’t aggressive enough and a top brass
that the naval historian Clay Blair argues failed to put a coherent plan together. Instead
boats were too often “shunted about willy nilly on missions for which [they were] not suited”.
Blair argues that the submarine force should have been overwhelmingly focused on interdicting
Japanese merchant shipping, particularly in the key area north-west of the Philippines.
He records that the 54 war patrols mounted into this region were responsible for 81 sinkings,
more than 40% of the total for the year. It was a pattern that Rear Admiral Charles
Lockwood, in command of the submarines based at Pearl Harbor learned from. In 1943 some 50%
of the patrols from Hawaii were directed to this key zone, compared to just 15% in 1942.
Lockwood himself was promoted to overall command of pacific submarines in February
after the incumbent Bob English and several other naval officers were killed in a plane crash.
Lockwood oversaw a better, but still inconsistent, year for the submarine fleet.
335 Japanese ships were sunk by submarines, with 135 added from other causes.
It was a big rise on the previous year, and enough to start to have an impact on the imperial
economy. Imports of key raw materials including coal, iron, bauxite and rice fell to 16.4m tons.
The americans were aided through 1943 by better availability of torpedoes, as the supply shortages
that had plagued the previous year eased. But though they had more torpedoes, the mark 14
was still not reliable, though more effort was put into fixing the issues as the year wore
on. All of the defects were eventually solved by September 1943- 22 months after the war had begun.
The improved fortunes of Allied Submarines in 1943 did not escape the attention of the Imperial
Japanese Navy. Towards the end of the year, the Japanese finally set up a dedicated force
to protect its merchant shipping- the ‘Merchant Escort Command’ under Admiral Koshiro Oikawa.
Japan entered World War 2 without an effective idea of how to protect its merchant shipping.
Commerce defence during a protracted, gruelling war had not formed a central part of a naval
strategy which emphasised fighting a single, decisive battle. As such, the resources that
Admiral Oikawa was able to command to protect Japan’s vital shipping were meagre at best. Of the
69 destroyers that Japan possessed at the outbreak of war, 38 had been sunk by the end of 1943,
so there was precious little to work with. Several classes of small escort ships were ordered,
but most of these were not complete until the latter half of the war. The Japanese also ramped
up construction of fresh merchant ships, being no longer able to rely on captured tonnage. More
than a million tons of shipping would be constructed between April 1943 and April 1944,
joined by increasing numbers of escorts as the new year approached.
But unfortunately for Japan, it would not be enough to prevent what was
coming. -
By the start of 1944, the United States’ Navies Pacific submarines were reaching a very high level
of efficiency. Problems with crews and torpedoes had been largely worked out. A developed system of
‘Wolfpacks’ had been implemented, with multiple boats co-ordinating attacks together. Superior
radar technology had been installed on many boats, and detailed information on Japanese movements
was provided by ULTRA decrypts from Bletchley Park. Through 1944 the subs demonstrated their
effectiveness against Japanese warships. They sank: 1 battleship, 7 aircraft carriers, 2 heavy
cruisers, 7 light cruisers and 30 destroyers. To this formidable force was added the key
ingredient of new air and sea bases on the Mariana islands of Saipan and Guam, captured in mid 1944.
The Mariana islands provided a staging base for naval and air forces that was dramatically closer
to Japan’s key shipping lanes than Pearl Harbor was. The impact on Japan’s shipping was even more
devastating than on its warships. From Submarines alone, 548 merchant ships were destroyed. Another
432 ships were sunk by other Allied combat units – mostly carrier and land based aircraft which
could now range deep into the east china sea. It was a devastating assault, that only got worse
as the year drew on. In the final months of 1944 US forces began to recapture the Phillippines.
With American forces based so close, the supply route to Japan north west of Luzon then became
almost completely severed, and the ability of Japan to transport vital oil virtually stopped
dead. Japanese imports for 1944 collapsed to 10m tons- a steep decline from the previous year,
and the size of the Empire’s merchant fleet more than halved from 4.1 to just 2m tons.
The impact on Japan’s war economy was profound. Production of steel and aluminium fell off a cliff
and the military’s stockpile of aviation fuel dropped to critical levels. By early 1945
effectively no oil was getting through to the home islands, which meant a critical shortage of fuel
to the point where the Japanese government began trying to extract oil from pine needles.
In other words, according to the historian Phillips Payson O’Brien, by the time the US
Air Force was even thinking about firebombing major Japanese cities “Japanese production was
already in a state of terminal collapse as their ability to move raw materials and finished goods
around their empire had ground to a halt”. It was nothing short of the total strangulation of a war
economy by air and sea, to such an extent that the submarine force actually had a quieter year
in 1945, sinking ‘only’ 160 ships or so. This was largely because what remained of
Japan’s merchant marine was bottled up in port, not daring to leave and being sunk
anyway in large numbers by aircraft and mines- which were dropped outside harbor entrances.
Across the war as a whole, Japan lost more than nine million tons of shipping, of which more than
6 million was sunk after the start of 1944. It was an utterly extraordinary success, and
one of the most important victories of the pacific war. With their war economy in ruins, the fighting
of 1944 and 45 became an increasingly uphill fight for the Japanese army and navy. For example-
shortages of fuel because tankers were getting sunk meant training for new Japanese pilots was
continually scaled back. Scaled back training meant inexperienced pilots getting massacred in
the skies above the phillippine sea in what became known to the US as the ‘marianas turkey shoot’.
However, important as it was the battle against Japanese shipping is also one of the least
known battles of the second world war. Unlike their German counterparts, the exploits of US
submarines were usually secret and not reported at the time, and in the years since the wars end,
historians and the public have often chosen to focus more on big decisive moments:
Midway, Leyte Gulf, Okinawa, Iwo Jima. But perhaps the most decisive battle of them all
was one that went on quietly under the waves, and brought the Japanese war economy to its knees.
We’re going to tell the story of one small part of this decisive battle in the next video- the story
of Commander Lawson Ramage’s 48 minute rampage through a Japanese convoy in the summer of 1944.
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