- [Jeremy] Being an island,
Britain had been traditionally reliant
on maritime communications.
It was for this reason
that she had always maintained a large navy.
In fact, Britain had the largest fleet in the world.
Therefore, sea power during World War II
was not significantly different
to that of the first World War.
As with the previous conflict,
the battleship remained the primary component
of the battle fleets.
The primary objective of the Royal Navy
was to destroy the German fleet
before it could cause any significant loss
to merchant shipping.
This meant that the German navy
would have to be strong enough to challenge
the Royal Navy in battle.
Grand Admiral Eric Raeder,
the Naval Commander In Chief,
was firmly convinced that the navy could never match
the British fleet on the surface,
because of the great limitations placed on it
after the Great War.
Instead, he believed that they should concentrate
on cutting the shipping and supply routes to Britain.
The German Naval Expansion Program Plan Zed
therefore represented a compromise.
Hitler was allowed to build a limited number of battleships,
and the first of them, the Bismarck,
was launched in February 1939.
Her sister ship, the Tirpitz,
went down the slipway two months later.
Raeder preferred the smaller pocket battleships,
which were thinly constructed but heavily armed.
Their high speed meant that they were ideally suited
to attacking the convoys.
Plan Zed was never completed,
but German warships were still a great menace
to British commerce.
In late 1939, French and British naval task forces
had to be used to hunt down the pocket battleship,
Graf Spee, which had been sinking merchant shipping
in the Indian Ocean and South Atlantic.
Four British cruisers based in the Fortland Islands
finally corned her at the mouth of the river plate
causing her crew to scuttle her.
In May 1941, the Bismarck played a cat and mouse game
with the British home fleet.
The battle cruiser Hood was her first victim.
Eventually crippled by a torpedo strike
from a British Swordfish,
Bismarck was finally sunk by the Royal Navy.
The British home fleet's attention now
gradually turned to German occupied Norway,
especially once the convoys to Russia had begun
in the late autumn of 1941.
In January 1942, the German battleship, Tirpitz,
was deployed to Norway
where she hid amongst the many fjords.
The Germans sent other warships.
These included the battle cruisers
Scharnhorst, Gneisenau, and Prinz Eugen,
which in February 1942 took the most direct route
up the English Channel from the French Port of Brest,
where they had been held at the mercy of RAF Bomber Command.
The Royal Navy, the Fleet Air Arm, and the RAF
were unable to stop them reaching the Baltic,
although both the Scharnhorst and the Genisenau
were damaged by mines on the evening of February the 11th.
The threat of these vessels to the Russian convoys
was to keep the home fleet on tenterhooks
until almost the end of 1944,
for it took all this time to destroy them.
On the last day of 1942,
the strong escort of a Russian convoy
managed to prevent the German cruisers
Hipper and Luetzow from attacking it,
an action that was named the Battle of the Barents Sea.
So disillusioned was Hitler by this failure
of his surface ships,
that he summoned Admiral Karl Doenitz,
head of the U-Boat Arm to replace Raeder
as Commander In Chief.
While Doenitz had always believed that the U-Boat
was the best means of defeating Britain,
he also realized the value
of maintaining the Norwegian threat
in order to prevent the British home fleet
from acting in other ways against Germany.
The British home fleet continued to use Russian convoys
At the end of 1943, it succeeded in tempting out
the Scharnhorst from her Norwegian anchorage.
The British intercepted and sank her
leaving only 36 survivors
in what became knows as the Battle of North Cape.
With the main threat to the Arctic now removed,
the Tirpitz was the only concern to the British.
In September 1943, the Tirpitz was attacked
by six midget submarines known as X-Craft.
This attack left the Tirpitz with serious damage
to her engines.
April 1944, having been repaired,
the Tirpitz was attacked once more
by British carrier borne aircraft.
Attacks on Tirpitz continued,
and in September she was badly damaged
when attacked by RAF squadrons with 12,000 pound bombs.
However, it was not until the 12th of November
that Tirpitz finally sank after an internal explosion,
and 1,000 of her crew perished.
Finally, the German surface threat from Norway
had been removed.
In the Mediterranean,
fleet versus fleet actions did take place.
The Royal Navy bombarded the French Fleet
in its Northwest African ports in July 1940
to prevent it falling into German hands.
It was an act that caused great anger in Vishay, France
But in November 1942,
the French scuttled their fleet in Toulon
after the Germans occupied Vishay, France.
The main naval action in the Mediterranean,
at least during the first half of the war,
was between the British and Mediterranean fleet
and the Italian navy,
which was determined to make the Mediterranean its sea.
It was a battle largely hinged on the British efforts
to keep their isolated but crucial
central Mediterranean foothold of Malta resupplied.
The running battle resulted in a large loss of ships.
Indeed, the British tactic was to use the Malta convoys
to provoke the Italians into a major fleet action.
Land-based Axis aircraft played a significant role
in harassing British ships.
But the two most significant naval actions
revealed that it was the British aircraft carriers
that were a key factor,
the Italians having none
of this type of vessel in commission.
In November 1940, Swordfish aircraft from the carrier,
Illustrious, attacked the Italian fleet base
in Taranto Harbor.
12 Swordfish took part.
Two were shot down, but they succeeded in severely damaging
three Italian battleships.
March 1941 saw the first proper fleet action
in which the Royal Navy had been involved
since Jutland in 1916.
The Mediterranean fleet managed to intercept the Italians
attempting to attack British Greece-bound convoys.
The British had three battleships,
and their warships sank two cruisers and two destroyers.
It was, however, aircraft from the carrier Formidable,
which after some maneuvering,
struck battleship Vittorio Veneto with a torpedo,
crippling the cruiser.
The British victory at Cape Matapan
insured that the Italian fleet stayed in port
for the next few months.
Using human torpedoes,
Italian Frogmen did, however,
sink the battleships Queen Elizabeth and Valiant
with limpet mines in Alexandria Harbor in December 1941.
It was the Pacific which really demonstrated
the dominance of the aircraft carrier,
which to this day remains.
Due to the success of the British attack
on Taranto in November 1941,
Japanese Admiral Yamamoto planned a similar surprise attack
on the American Pacific fleet base
at Pearl Harbor in Hawaii, known as Plan Zed.
The Japanese attacked Pearl Harbor in December 1941,
destroying much of the US Pacific fleet.
Plan Zed appeared to have succeeded,
but the Japanese missed the two vital fleet carriers,
Lexington and Enterprise,
which were at sea at the time.
It was around these two that the fleet was rebuilt.
The Americans were ready to confront the Japanese
by the Spring of 1942.
The Battle of the Coral Sea in May
and the Battle of Midway in June
faltered Japanese expansion
and enabled some measure of control to be regained
over the Southwest Pacific.
(plane engines whir)
These battles marked the beginning
of a new naval warfare.
Carriers took over from the battleships,
and the opposing fleets never came
within gun range of each other.
(plane engines whir)
There was a distinct pattern to these actions.
First, the opposing fleet had to be located,
done either by reconnaissance aircraft or submarine.
Then the first wave of aircraft was launched.
Dive and torpedo bombers were the two types
of carrier attack aircraft.
Fighters, like Japanese Zeros,
gave protection to the attack planes.
To give greater range,
aircraft were often fitted with additional fuel tanks.
Carriers were at their most vulnerable
when their aircraft were on the flight deck
being rearmed and refueled.
Should an imminent enemy air attack
be identified by radar,
it was crucial to get the fighters into the air
before it arrived.
Expert judgment was required to decide
which aircraft to have on deck at any particular time.
The great carrier battles eventually
broke the back of the Japanese navy.
One of the two major landmarks for the Americans
was the Battle of the Philippine Sea in June 1944,
which resulted in the capture of the Marianas,
known as the Great Marianas Turkey Shoot.
The other important engagement
was the Battle of Lady Gulf in the Philippines
in October 1944,
which totally crippled the Japanese fleet.
The American third and fifth fleets
succeeded in obliterating the remainder
of the Japanese carrier force over a period of four days,
resulting in the appearance of Japanese suicide pilots.
Japanese Kamikaze, or divine winged aircraft,
were to be the greatest threat to allied shipping
for the last year of the war in the Pacific,
designed to destroy enemy ships by diving onto their decks.
During the Battle For Okinawa,
from April to June 1945,
nearly 2,000 Japanese suicide sorties were mounted,
25 allied ships were sunk, and over 250 were damaged.
By Spring 1945,
the British Pacific Fleet had joined the American fleets
in the Pacific
to create the largest armada of warships ever known.
Consisting of over 1,300 ships,
it had a vast fleet train of support vessels
ranging from oilers to dry docks,
everything required to maintain a fleet
many thousands of miles away from its base.
One advantage that the British fleet carriers had
over those of the Americans was armored decks,
which were better able to resist Kamikaze attacks.
The threat of air power to navies
had forced every warship of whatever type
to be armed with an increasing number
of anti-aircraft weapons.
The British even went so far
as to produce anti-aircraft cruisers
with high angled gun turrets, like the Dido Class vessel.
Battleships still had a part to play
despite the increasing use of the carrier.
They had found themselves a new role, shore bombardment,
both in the European theater and in the Pacific.
Their way to fire could prove devastating
in support of land operations.
To give up one example,
the Germans in Normandy,
during an arf of the allied landings in June 1944,
considered that the weight of naval gunfire
was much more a factor for concern
than the total allied air dominance
over the battle area.
Naval support for ground forces
extended much further than just shore bombardments.
During the early part of the war,
the Royal Navy found itself having to evacuate
allied forces after disastrous campaigns.
The evacuations from France in 1940
and Greece and Crete in 1941
were carried in an environment
in which the Axis had air superiority
and a cost in ships was high.
The Japanese in the Pacific
used light cruisers and destroyers extensively
to keep isolated island garrisons supplied.
The so called "Tokyo Express"
was especially successful in this
during the long battle for Guadalcanal
in the Solomon Islands in the second half of 1942.
But both in Europe and the Pacific,
the second world war came to be dominated
by amphibious operations,
the landing of ground forces on hostile shores.
Indeed, there was no theater of war
in which these did not take place.
The Russians carried out a number in the Black Sea.
The British mounted them on the Coast of Burma.
The navy's first task in these operations
was to ensure that it dominated the adjoining seas.
The one exception to this was
during the first amphibious landings of the war
by the Germans in Norway in April 1940.
They lost a number of ships to the guns of the Royal Navy,
enabled them to achieve their objectives.
Many of the major naval actions in the Pacific
were fought to ensure
that the US Navy had this necessary dominance.
The British experience in the Dardanelles in 1915
had caused many to believe
that landings on opposed shores were not feasible.
As a result, pre-war policy gave little priority
to amphibious operations.
In 1939, no nation had much in the way of landing craft,
flat bottomed to enable them to be driven up onto a beach,
so that the troops could land
without getting their feet wet.
The momentum came from Britain
with the formation of the Commandos in the Summer of 1940,
in order to carry out raiding operations
against Axis-held coasts.
In conjunction with this,
Churchill set up the Directorate of Combined Operations.
It's title emphasized the fact
that amphibious warfare involved all three armed services,
air, sea, and land.
Through this medium,
a wide range of amphibious shipping was developed.
Once America entered the war,
she was also able to harness a significant part
of her industrial know-how to this field.
Largest were the assault ships
which took troops, equipment, and supplies
from the mounting base to the landing area.
On arrival to the landing area,
the navy began to bombard the shore
in order to neutralize the defenses.
The assault ships carried landing craft,
and it was to these that the troops now transferred.
(boat engines roar)
Smaller types, like the landing craft, Assault,
were used for raiding operations.
And there were ocean-going landing ships,
which could put tanks and guns directly ashore
onto the beaches.
There were also landing craft
equipped with guns and rockets
to add to the supporting fire
as the landings took place.
Once the landings had taken place,
the beaches themselves needed to be properly organized.
If not, chaos would very quickly be the result.
The British formed the Royal Navy Beach Head Commandos
for this task.
The US Navy's Construction Battalions, the Seabees,
were adept at clearing beach obstacles
and opening up harbors and building air fields.
By 1945, the western allies had overcome
the complexities of amphibious warfare
and developed it into a fine art.
The main key to success
was the close coordination of land, sea, and air forces.
Indeed, in no other operation of war
was and is this more vital
from the planning stage, the landing stage,
and through to the subsequent operations on the land.
The successful conduct of amphibious operations
became the cornerstone of allied strategy
in the second world war.
As American General Douglas MacArthur later said,
"the amphibious landing is the most powerful tool we have."
The throttling of maritime communications
was pursued by navies in the second world war
with an even greater intensity
than during the first world war.
The Germans recognized,
as they had done during the Great War,
that the one way to bring Britain to her knees
was to paralyze her trade routes.
Her second Battle of the Atlantic was waged.
It opened with the sinking of the liner, the Athenia,
on the third of September 1939.
It did not end until after the sinking
of two British merchant vessels
off Scotland's east coast on the seventh of May 1945.
It was the longest campaign of the second world war.
At the beginning, the German submarine fleet was small
with only 57 U-boats in commission,
and just a third of these at sea.
But Hitler also believed that his major surface warships
could play a significant part
in attacking merchant shipping.
Indeed, the Graf Spee and the Deutschland
had sailed from Germany before the outbreak of war
for this very purpose, and was soon sinking ships.
The Royal Navy, on the other hand,
had grown complacent between the wars
over their trek to trade.
Their institution of convoying
and the invention of ASDIC,
called Sonar by the Americans,
averted the danger and led to the defeat of the U-boat.
Convoying was instituted as soon as the war broke out,
but there was a grave shortage of escort vessels
with most commissioned to other tasks,
such as escorting the British Army across to France.
Consequently, transatlantic convoys
were restricted to vessels with a speed of nine to 15 knots.
Then their sole support was often no more
than a single armed merchant cruiser.
The U-boats were thus able to concentrate
on the numerous vessels sailing on their own.
By the end of 1939,
the U-boats had sunk over 100 vessels,
while the British had little success
in hunting them down.
Their attempts to use carrier routes against the U-boats
were especially disastrous,
with one carrier sunk and a near miss on another
in the first weeks of the war.
In the meantime, the Graf Spee in the South Atlantic
and Deutschland in the North Atlantic
were joined in November by the Scharnhorst
and the Gneisenau.
By the end of 1939,
they had accounted for 15 merchant vessels.
(eerie music) (waves crash)
The severe winter weather reduced operations,
as did the Norwegian campaign in spring 1940.
(eerie music) (waves crash)
Mine warfare was also used extensively
by both sides from the outset of the war.
Each played its part in the campaign against trade,
accounting for 79 allied vessels
during the first four months.
The magnetic mine was the cause of many casualties.
(eerie music) (waves crash)
This mine was initially very difficult to sweep,
except by vessels with all wooden hulls.
To counter a magnetic mine,
the British had to run electric coils
around the hulls of their ships
in order to cancel out the magnetic signature
which detonated this type of mine.
This was known as degaussing.
The next major phase of the Battle of the Atlantic
began in the summer of 1940 after the fall of France.
This enabled the Germans to deploy their U-boats
to the French Atlantic ports
and radically reduce the time used
to deploy them into the Atlantic,
meaning that many more U-boats could be on patrol
at any one time.
This period was the beginning
of what the U-boat Skippers called "the first happy time."
(eerie music) (waves crash)
The British were still dreadfully short
of escort vessels,
even though the American donation of 50 World War I
force attacker destroyers in September 1940 did help.
The Germans, too, had positioned a squadron
of huge Focke Wulf Condors on the French Atlantic coast.
These were able to guide the U-boats onto the convoys,
besides accounting for
a significant number of ships themselves.
There was also the surface threat
with the German pocket battleship Admiral Scheer
sinking no less than 17 vessels during one cruise
in November 1940.
Early in 1941, the Scharnhorst and the Gneisenau
disrupted the entire British convoy system.
The Germans also employed commerce raiders,
merchant vessels armed with obsolete 150 millimeter guns.
Most successful of these was the Pinguin.
She sank no less than 26 vessels
using her Arado 196 float plane to locate her victims.
Royal Navy ships searched for her in the Indian Ocean.
In May 1941, the Pinguin was finally intercepted
by the cruiser Cornwall,
who succeeded in causing her to sink.
By this time, more escort vessels were becoming available,
basing some in Iceland and using the increasing resources
of the Royal Canadian Navy,
enabled convoys to be given much more protection
Aircraft, like the American-built Lockheed Hudsons,
were deployed in Iceland
to provide more air cover over the Atlantic.
There was also the surrender of the U-11O.
Before she sank, the British managed to seize her
Enigma Cipher Machine.
This enabled them to read U-boat signals,
and hence, re-route convoys.
The net result of all this was that by July 1941,
shipping losses had fallen to a fifth
of what they had been in March.
In the meantime,
RAF Bomber Command was attacking the shipyards,
building U-boats, but without much success.
Likewise, the reinforced concrete pins,
in which they were housed in the French ports,
proved to be resistant to bombing.
President Roosevelt gave increasing help
as 1941 wore on,
even though the United States were still at peace.
Unlike many Americans, he believed that sooner or later
his country would get drawn into the war.
In July, US Marines began to relieve
the British Garrison on Iceland.
This meant that the US Navy could legitimately
escort convoys there.
Later, Roosevelt extended this by declaring
that he would provide escorts for any land-leased convoy
across the Atlantic to as far west as level with Iceland.
It was virtually inevitable that US warships
would be attacked.
On the 17th of October, the destroyer Kearny, seen here,
was badly damaged by a U-boat.
Two weeks later, another destroyer, Reuben James,
But it was Japan, and not Germany,
that forced America into the war
through the surprise attack on Pearl Harbor.
This precipitated the second happy time
for Germany's U-boats.
Admiral Karl Doenitz, their commander,
turned his eyes on the poorly protected
American eastern seaboard,
and especially on the tanker traffic from South America.
He deployed a number of his ocean-going Type IX boats,
and in January 1942, they launched Operation Drum Roll.
That month alone, they sank 40 ships in these waters.
Worse, on the first of February,
the U-boats adopted a new Enigma Cipher,
which the British were unable to decode
until the end of that year.
Not until April was a blackout of lights
on American eastern seaboard instituted
together with a proper convoy system.
Thereafter, the U-boats moved to the Caribbean,
where there were equally rich pickings to be had.
Doenitz also began to deploy U-boat tankers,
known as Milk Cows,
which could carry 600 tons of fuel, torpedoes,
and other supplies to keep the U-boats resupplied.
This enabled him to deploy the more numerous,
but shorter ranged, Type VIIs.
Doenitz was convinced that his U-boats
would be at their most effective
if they were concentrated in what he called Wolf Packs.
Not until 1942 did he have sufficient operational U-boats
to be able to put this into wide scale practice.
The Wolf Packs would form a patrol line,
with the boats usually positioned at five mile intervals.
They will then sweep eastwards and westwards
until they contacted a convoy.
But the escorts in the convoys themselves
were becoming better organized.
Convoys were graded fast and slow,
with only fast troop ships
being allowed to travel on their own
since they could outrun the U-boats.
Their hub of operations was Headquarters Western Approaches,
based in the English port of Liverpool.
Their convoy commander was usually
a senior retired naval officer.
And before the convoy set off,
he would brief the merchant captains.
On both sides of the Atlantic,
local escorts saw the convoys and their columns of ships
out of coastal waters.
The ocean escorts then took over.
These usually consisted of some six destroyers,
corvettes, and sloops.
By the second half of 1942,
they were becoming well drilled
and able to carry out combined attacks on U-boats
on a single code word.
Sonar remained the main means
of detecting a U-boat underwater,
but escorts were now beginning to be equipped with radar
to locate a surfaced U-boat.
High Frequency Direction Finding, or Huff-Duff,
enabled them to pinpoint a U-boat's position
from its radio transmissions.
In the early part of the war,
escorts could only fire depth charges over the stern,
which meant that they first had to pass
over the U-boat.
This gave the U-boat more time to take evasive action.
By mid 1942, however,
anti-submarine attacks could be made over the sides
and bow of the escort,
which increased the chances of a kill.
But it was recognized by now
that air cover was essential
to ensure the safety of a convoy.
Even with new maritime patrol aircraft,
like the resilient American-designed PBY one,
called the Catalina by the British,
there was still an area of the North Atlantic
that was not under land-based aircraft coverage.
This was known as The Black Gap.
To overcome it,
the British initially introduced
Catapult-Armed Merchant Men, known as CAM Ships.
These carried a single hurricane,
which could be launched from the deck,
but on return,
this had to ditch alongside its parent vessel.
Later, escort carriers smaller than the fleet carrier
were built in large numbers
by both the Americans and the British.
It was not, however,
until 1943 that the Black Gap was closed
when very long range B-24 Liberator were deployed,
but sinkings were continuing to outstrip
the build of new merchant vessels.
American Industrial Organization came to the rescue
with shipyards on both sides of the Atlantic,
bursting at the seams to meet the now very varied
allied naval demands.
The Americans came up with a new idea
for constructing merchant vessels.
They were allowed to be built at factories inland
These would then be taken to the coast and assembled.
The first Liberty ship, the Patrick Henry,
was launched from Baltimore Naval Dockyard
as early as September 1941.
Thereafter, production increased rapidly,
and by the end of 1942,
it was beginning to have a very real effect
on the Battle of the Atlantic.
The winter of 1942-43, with its Atlantic gales,
helped to reduce shipping losses.
So too, did the fact that the British
had finally cracked the U-boat Tritan Engima Cipher.
In January 1943, at the Allied Conference
held at Casablanca,
it was agreed that winning the Battle of the Atlantic
must be a top priority.
At the same time, Doenitz,
who had now taken over as Commander In Chief
of the German navy,
ordered his U-boats to concentrate
just on the fully-laden convoys
crossing from North America to Europe.
Sinkings in the North Atlantic now rose alarmingly.
The real crisis came in mid March,
when no less than 37 U-boats hurried to east-bound convoys,
sinking 21 ships.
A total of 540,000 tons of allied shipping
was lost during the month.
Only the arrival of the spring gales
put a break on U-boat activity.
In desperation, the British halted their convoys to Russia
in order to provide more escort vessels for the Atlantic.
Some of these were formed into support groups
which could reinforce convoys under severe attack.
Once the gales ceased,
Doenitz deployed an increasing number of U-boats.
Their climax came at the beginning of May 1943,
when no less than 40 U-boats
attacked the west-bound convoy, ONS 5,
sinking 12 ships in 36 hours,
but losing two of their own.
But then the escorts struck back,
sinking four more U-boats
and damaging several others without loss.
This sudden change in allied fortunes in the Atlantic
was to continue for the next two weeks.
More and more U-boats failed to return to their bases.
Eventually, on the 24th of May,
having lost a staggering 31 U-boats so far in the month,
Doenitz decided to temporarily withdraw his Wolf Packs
from the Atlantic.
It was the major point in the battle,
but by no means the end of it.
In September 1943, the U-boats returned to the Atlantic,
this time equipped with a new acoustic torpedo.
But the Allies were able to counter this with a drogue
designed to reproduce the noise of a ships engine,
and which was towed by an escort vessel.
The Germans then introduced snorkels on their U-boats,
which enabled them to spend more time under the water.
Finally, in mid 1944, came the new Electroboat,
capable of underwater speeds of up to 17 knots,
but this and the even faster Walter Boat,
which was driven by hydrogen peroxide when submerged,
appeared too late to altar the course of the campaign.
The cost of the Battle of the Atlantic
was high for both sides.
Of the nearly 1,200 U-boats commissioned during the war,
no less than 65 percent were lost,
yet 23 million tons of allied shipping had been sunk,
15 million of it in the North Atlantic.
The Mediterranean, too, saw much submarine activity
during the first half of the war.
Axis submarines concentrated on ravaging
the weak British supply line to Malta
and had some notable successes.
In November 1941,
German U-boats accounted for their carrier, Ark Royal.
12 days later, U-331 sank the battleship Barham.
In turn, British submarines hurried
the Axis sea communications to North Africa.
By the autumn of 1942, they had,
with the help of aircraft,
almost severed fuel supplies to Rommel's Army,
and forced him onto the defensive.
In the Pacific, the submarine also played a key role.
The Japanese entered the war with 64 boats,
more than the Germans had in 1939.
A further 126 were built during the war,
but almost 70 percent of their total build was lost,
sinking less than a million tons of allied shipping.
The main reason for this poor performance
was that the Japanese placed priority
on attacking warships,
rather than defenseless merchant and supply vessels.
They also generally organized their submarines
in rigid groups,
and allowed their skippers
very little attitude or initiative.
Many Japanese submarines were also lost
in carrying out resupply missions to isolated garrisons.
And as many as 20 at a time were used
to keep their own forces supplied
during the long battle for Guadalcanal.
Most of these subsequently fell victim
to American warships.
If the Japanese submarine fleet failed
to make a significant contribution to the war effort,
the American submarines most certainly did.
Recognizing that Japan's war industry
was totally dependent on the import of raw materials,
the US Navy decided to concentrate submarine operations
on attacking Japanese merchant shipping.
This resulted in serious problems
with malfunctioning torpedoes.
These problems were not resolved until 1943.
Even so, during 1942, American submarines sank
180 Japanese merchant vessels.
Two years later, with the underwater fleet having expanded,
the Allies were able to operate from forward bases
in the Pacific,
and American submarines sank a colossal total of 600 ships,
and then began to run out of targets.
This reduced Japanese imports by 40 percent,
including oil supplies,
so that the Japanese main fleet had to base itself
in the Dutch East Indies,
rather than home waters,
in order to insure that it continued to receive fuel.
Japanese war production, as a whole,
was halved by spring 1945,
and oil shortages had crippled the transportation system.
In contrast, because of the American success,
the US Submarine Production Program
was drastically cut back in 1944.
the American submarines in the Pacific succeeded,
where the German U-boats in the Atlantic had failed.