Battle of the Atlantic
is the name
given to the conflicts in the Atlantic Ocean throughout World War II.
Britain, as an island nation, has always been highly dependent on sea-going
trade. During WWII this was even more the case, and Britain needed to import
over 1 million tons of supplies every week to be able to feed and equip
its population and war machine.
The day that war was declared between Britain and Germany, the first
action of the naval campaign started. British naval vessels dredged up
and cut German transatlantic communication cables, forcing the Germans
to communicate to their interests in the Americas by less secure means
for the rest of the war.
The mining threat
Much of the early action by German forces involved mining convoy routes
and ports around Britain. The U-boat fleet, which was to dominate so much
of the battle of the Atlantic, was very small at the beginning of the war.
Mines could be laid by boats, by aircraft, and also by submarines.
The mining was highly effective, and initially involved the use of contact
mines, which meant that a ship had to physically strike one of the mines
in order to detonate it. In most cases the mines were placed in "friendly"
waters to defend against enemy ships and submarines, where they were suspended
on the end of a rope or chain just below the surface of the water. By WWII
most nations had also developed mines that could be dropped from aircraft,
which could then be placed in enemy harbours although they simply floated
on the surface. The use of dredging and nets was effective against this
type of mine, but nonetheless was time-consuming, and involved the closing
of harbors whilst it was completed.
Into this arena came a new mine threat. Most contact mines leave holes
in ship's hulls, but some ships surviving mine blasts were limping back
to port with buckled plates, popped rivets, and broken backs. This appeared
to be due to a new type of mine that was detonating at a distance from
the ships, and doing the damage with the shockwave of the explosion.
These mines were devastating; often ships that had successfully run
the gauntlet of the Atlantic crossing were destroyed entering freshly mineswept
harbors on Britain's coast. More shipping was now being lost than could
be replaced, and Churchill ordered that the recovery, intact, of one of
these new mines was to be given highest priority.
Then the British experienced a stroke of luck in November 1939. A German
mine was dropped from an aircraft laying mines onto mud flats in the Thames
estuary, well above the waterline. As if this was not sufficiently good
fortune, the land happened to belong to the army, and a base, including
men and workshops were close at hand.
Experts were quickly dispatched from London to investigate the mine.
They had some idea by this time that the mines used magnetic sensors, so
they had everyone remove all metal, including their buttons, and made new
tools out of non-magnetic brass. They then safed the mine and rushed it
to labs at Portsmouth, where scientists discovered a new type of arming
The arming mechanism had a sensitivity level that could be set, and
the units on the scale were milligauss. Gauss is a measurement for the
strength of a magnetic field, and so they knew why it went off before coming
into contact with the ship. Using the detector from the mine, they were
able to study the effect of a ship passing over it. A ship, or any large
ferrous object passing through the earth's magnetic field will concentrate
the field at that point. The detector from the mine measured this effect,
and was designed to go off at the mid-point of the ship passing overhead.
From this crucial data, methods were developed to clear the mines. Early
methods included the use of large electromagnets dragged behind ships,
or on the undersides of low-flying aircraft (a number of older bombers
like the Vickers Wellington were used for this purpose). However both of
these methods had the disadvantage of "sweeping" only a small strip at
a time. A better solution was found in the form of electrical cables dragged
behind ships, passing a large current through the seawater. This induced
a huge magnetic field and swept the entire area between the two ships.
The older methods continued to be used in smaller areas, the Suez Canal
continued to be swept by aircraft for instance.
While these methods were useful for clearing mines from local ports,
they were of little or no use for enemy controlled areas. These were typically
visited by warships only, and the majority of the fleet then underwent
a massive de-gaussing process, where their magnetic fields were reduced
to such a degree that it was no longer "noticed" by the mines. This started
in late 1939, and by 1940 British warships were largely immune for the
few months at a time until they once again built up a field. Many of the
boats that sailed to Dunkirk were de-gaussed in a marathon four-day effort
by hard-pressed de-gaussing stations.
The Germans had also developed a pressure-activated mine and planned
to deploy it as well, but they saved it for later use when it became clear
the British had beaten the magnetic system. They were then sown across
likely invasion areas off the coast of France. This system had the disadvantage
of requiring a periodic resetting of the trigger mechanism, so they were
attached to chains and cables so they could be pulled to the surface and
reset. Unlike the contact mine, however, in this case the mine lay on the
ocean floor, and the cable ran to a float on the surface.
In 1944 General Erwin Rommel timed the resetting so that the mines would
be at their best effectiveness during late April and into May - the best
time for an allied invasion of France during the early summer. In June
they were getting past the point of effectiveness and he ordered them pulled
in for maintenance. The allies launched D-Day on June 6th, and the mines
could not be replaced until it was too late.
The happy time
Prior to the war the admiral of the U-boats, Karl Doenitz, had advocated
a system known as the wolfpack
, in which teams of U-boats would
gang up on convoys and simply overwhelm the defending warships accompanying
them. He also developed a theory of destroying an enemy fleet, not by attacking
their ships directly, but by cutting off their supplies so they could not
be used – an economic war. In order to be effective he calculated
that he would need 300 of the latest Atlantic Boats
(the Type VII),
which would create enough havoc among British shipping that she would be
knocked out of the war.
However the U-boat was still looked upon by much of the naval world
as a poor-man's weapon, and deliberately hunting merchant ships to be used
only by cowards. This was true in the Kriegsmarine as well, and the Grand
Admiral, Erich Raeder, successfully lobbied for monies to be spent on large
capital ships instead. These were of even more dubious use considering
the huge British fleet facing them, and even Raeder himself suggested they
would be wiped out very quickly in the event of war.
Thus the U-boat fleet started the war consisting mainly of the short
range Type II which was useful primarily for mine-laying and operations
in and around the British coastal areas. They had neither the range nor
the supplies to operate far from land, and as a result the RAF was able
to counter the U-boats to some degree with standing patrols by Coastal
Command aircraft. Early operations of aircraft against the U-boats were
somewhat comical, but the crews gained experience quickly and the Western
Approaches were soon cleared of the threat.
Meanwhile Royal Navy destroyers were being equipped with increasingly
powerful sonar systems (known to the RN as ASDIC) and were able
to block the exits into the North Sea and the Channel with some success.
ASDIC was unable to find U-boats on the surface where they spend the vast
majority of their time, but with aircraft cover forcing them underwater,
running to the Atlantic could be a somewhat dangerous operation.
However with the fall of France the Kriegsmarine gained direct access to
the Atlantic ocean. Huge fortified concrete ports for the U-boats were
built, which resisted any successful bombing throughout the course of the
war. Most of the U-boat fleet was moved to these bases where they also
had excellent air cover, making it much harder for both the RAF and RN
to do anything about it.
In addition the new Type VIIc design started arriving in large numbers
in 1940. The VII was much more powerful than the Type II it replaced, including
both a rapid-fire 88mm deck gun and four forward tubes. It also was much
larger than the Type II, and could spend long times at sea, well away from
land. Earlier VIIa and VIIb's had already reached service in small numbers,
but the c was put into full production and eventually 585 of them would
The Type VII dramatically increased the problems for the British. The
boats would operate long distances from shore, meaning that they were well
out of the range of land-based aircraft to harass them. The only counter
was the Royal Navy's ships, but there were far too few of them to cover
the vast amount of the sea that these boats operated in.
The RN had yet to institute the policy of convoys, primarily because
it slows all of the boats down to the speed of the slowest member. The
few Type VII's already delivered were able to escape into the Atlantic
at night and then wait for ships to pass. They would then run on the surface
and hunt down the scattered cargo ships with their gun. The early operations
were spectacularly successful, and the U-boat crews were heroes to the
people in the motherland. The crews referred to this as the 'happy time'.
The RN quickly introduced a convoy system which allowed them to concentrate
their warships near the one place the U-boats were guaranteed to be found
– the convoys. This had some effect, but not what they had hoped.
The speed of these newer boats compared to their WWI counterparts meant
that they could often run to the front of the convoy, wait for the convoy
to sail into into torpedo range underwater, fire a salvo, and leave long
before the escorts could get to them.
However the German effort also had problems of its own. Their torpedoes
continued to fail with an alarming rate, and the director in charge of
their development continued to claim it was the crews' fault. Eventually
this came to a head when one U-boat ace shot three perfect hits into the
side of the HMS Ark Royal, only to watch all three explode harmlessly far
away from the ship's side. Scenes like this continued until the matter
was finally taken to hand in April 1940, although it wasn't until early
1942 that the problems were completely addressed.
Another issue was finding the convoys in a very large ocean. The Germans
had nowhere near the number of patrol boats or tracking stations needed
to make accurate fixes from shore. Instead they had a small handful of
very long range aircraft (namely the Fw 200 Condor) used as spotters. To
this they added codebreaking efforts, which eventually succeeded in breaking
the British Merchant Marine code book, allowing them to time the convoys
as they left North America from Halifax, Nova Scotia.
But the primary source of tracking was the U-boats themselves. They
were strung out in lines across the North Atlantic waiting for a passing
convoy. When spotting one, they would radio the position back to Kriegsmarine
headquarters, where a furious effort would break out to vector other U-boats
onto the attack. As the numbers of U-boats and the proficiency of the headquarters
grew, they were eventually able to consistently form the wolfpacks that
At the same time a number of technical developments looked set to aid
the Allies. Firstly, new depth charges were developed that fired in front
of the destroyers rather than simply dropping them over the side as the
destroyer passed over. The sonar contact was lost directly underneath the
boat, and the U-boats often used this to escape. In addition, depth charges
were fired in patterns, to 'box' the enemy in with explosions. The shockwaves
would then destroy the U-boat by crushing it in the middle of these explosions.
A device used to achieve this was called Hedge-hog, a nick-name
derived from the firing spindles. This fired twelve charges at precisely
timed and angled trajectories to hit a point in front of the ship.
Aircraft ranges were also improving all the time, but the Atlantic was
far too large to be covered completely (at the time). A stop-gap measure
was instituted by fitting ramps to the front of some of the cargo ships
known as CAMs, armed with an obsolete plane such as the Hawker Hurricane.
When a German spotter plane approached, the fighter was fired off the end
of the ramp with a large RATO rocket, eventually ditching in the water
to allow the pilot to be picked up by one of the escort ships.
One of the most significant developments was improved direction-finding
radio equipment. A new design enabled the operator to instantly see the
direction of a broadcast. Since U-boats had to surface to radio, they gave
their positions away as soon as they radioed in the position of a convoy.
A destroyer could then engage the U-boat, preventing a coherent attack
on the convoy.
In general the Royal Navy slowly gained the upper hand through until
the end of 1941. Although they were doing limited damage to the U-boats
themselves, they were managing to keep them from the convoys to an increasing
degree. Shipping losses were high, but managable.
This changed when the US joined the war, by declaring war against Japan
in retaliation for Pearl Harbor. Germany then declared war on the US and
promptly attacked US shipping.
Dönitz had only 12 boats of the Type IX class that were able to make
the long trip to the US east coast, and half of them were removed by Hitler's
direct command to counter British forces. One of those was under repair,
leaving only five ships to set out for the US on the so-called
Drumbeat (Paukenschlag). What followed is considered by many
to be one of the most victorious naval campaigns since the Battle of Trafalgar.
The US, having no direct experience of modern naval war on its own shores,
did not employ shore-side black-outs. The U-boats simply stood off the
shore of the eastern sea-board and picked off ships as they were silhouetted
against the lights of the cities. Worse, the US commander, King, was a
terrible anglophobe and rejected the RN's calls for a convoy system out
of hand as the whimperings of weaklings. Instead he saved the US's destroyer
fleet for action in the Pacific against the Japanese, leaving the U-Boats
free to do what they wanted.
The first boats started shooting on January 13th, 1942, and by the time
they left for France on February 6th they had sunk 156,939 tonnes of shipping
without loss. After six months of this the statistics were equally grim.
The first batch of Type IX's had been replaced by Type VII's and IX's refueling
at sea from modified Type XIV Milk Cows (themselves modified Type
IX's) and had sunk 397 ships totalling over 2 million tons.
It wasn't until May that King saw the error of his ways and instituted
a convoy system. This quickly led to the loss of seven U-boats. But the
US did not have enough ships to cover all the holes, and the U-boats continued
to operate freely in the Caribbean and the Gulf of Mexico (where they effectively
closed several US ports) until July.
The U-boat crews called this the second happy time.
Operation Drumbeat did have one other effect. It was so successful that
Dönitz's policy of economic war was seen even by Hitler to be the only
effective use of the U-boat, and he was given complete command to use them
as he saw fit. Meanwhile Dönitz's commander, Raeder, was being demoted
as a result of a disastrous operation in which several German capital ships
had been beaten off by a small number of RN destroyers. Dönitz was eventually
made Grand Admiral of the fleet, and all building priorities turned to
With the US quickly arranging convoys, ship losses to the U-boats quickly
dropped and Dönitz realized his boats were better used elsewhere. At the
end of July 1942 he shifted attention back to the North Atlantic, where
the battle would enter its final terrible phase.
By this point there were more than enough U-boats spread across the
Atlantic to allow several wolfpacks to attack the same convoy. In most
cases 10 to 15 boats would attack in one or two waves, following the convoys
by day and attacking at night. Losses quickly started ramping up, and in
October 56 ships of over 258,000 tones were sunk in the limited area between
Greenland and Ireland that was still free of the ever-increasing allied
Operations died down over the winter, but in the spring they started
up again with the same ferocity. In March another 260,000 tones were sunk,
and the supply situation in England was such that there was talk of being
unable to continue the war effort. Supplies of fuel were particularly low,
and any attempt to form massive US armies in England were hopeless.
It appeared that Dönitz was winning the war. And yet March was the
end of the battle. In April losses of U-boats shot up while their kills
ships fell dramatically. By May the wolfpack was no longer. The Battle
of the Atlantic was won by the allies in two months.
There was no one reason for this, but a number of them that conspired
to all take effect at almost the same time. The result was a huge blow
that Dönitz was unable to recover from. The four major changes were largely
Among these was the introduction of an effective sea-scanning radar
small enough to be carried on the patrol aircraft. Although they had long
been known to be able to detect a surfaced boat from many miles, the aircraft
themselves had limited range. This changed with the improved supply of
the very long range Shorts Sunderland and B-24 Liberator aircraft, which
could cover much larger areas of the ocean.
But even they couldn't cover it all. The remaining holes were closed
by the introduction of the small escort carrier. Flying Grumman Avengers
primarily, they formed into the same convoys and provided air cover and
patrol all the way across the Atlantic.
In addition the British introduced the new River class frigates, built
with a single purpose in mind - killing U-boats. They were faster, better
armed, and had better radar and ASDIC. Formed into hunter-killer groups
(one of the major tactical reasons for the victory) by the new commander
of the Western Approaches, they would sail far from the convoys in small
groups, making it almost impossible for the wolfpacks to form up under
their constant harassment.
But by far the single biggest element to the victory was the cracking
of the Enigma code machine. This had been a running battle between upgrades
to the machine and British efforts to crack it, dating back well before
the war. By 1943 the machine had lost the race and an increasing amount
of German naval radio traffic was being read. The Royal Navy knew where
the packs were forming and sent in the hunter-killer groups to destroy
The efforts were so successful that it's a wonder the Kriegsmarine didn't
realize that this was happening. It appears that they seemed to have some
idea, but repeated questions by Dönitz sent to German's intelligence services
always resulted in claims there was no way the code could be broken. One
would think that simply looking at the statistics would be enough –
U-boat losses dropped every time a new version of the code was introduced
– but time lags, luck, pigheadedness, and astounding efforts
on the British part kept this from ever becoming clear.
In the next months the vast majority of the U-boat fleet would be sunk,
typically with all hands.
With the battle won, US supplies started to pour into England for the eventual
invasion of France. This was clear even to the Germans, who became desperate
to re-start the battle.
Several attempts were made to salvage the Type VII force. Notable among
these attempts were the fitting of massively improved anti-aircraft batteries,
radar detectors, and finally the addition of the Schnorkel device to allow
them to run underwater off their diesel engines to avoid radar.
None of these were truly effective however, and by 1943 allied air power
was so strong that the U-boats were being attacked right in the Bay of
Biscay as they left port. Their short lives consisted of watching in fear
until they were sunk by the one plane they didn't see.
The last, and most impressive, attempt to re-open the battle is the stuff
of legend. Since even before the war the rocket designer Hellmuth Walter
had been advocating the use of hydrogen peroxide (known as Perhydrol
as a fuel. His engines were to become famous for their use in rocket powered
aircraft - notably the Me 163 Komet - but most of his early efforts were
spent on systems for submarine propulsion.
In these cases the hydrogen peroxide was reduced and the resulting gases
used to spin a turbine at about 20,000rpm, which was then geared to a propeller.
This allowed the submarine to run underwater at all times, as their was
no need for air to run the engines. However the system also used up tremendous
amounts of fuel, and any boat based on the design would either have to
be absolutely huge, or have terribly limited range.
Thus the system saw only limited developement even though a prototype
was running in 1940. But when problems with the existing U-Boat designs
became evident in 1942, the work was stepped up. Eventually two engineers
came up with a simple solution to the problem.
Instead of running the submarine 100% on the perhydrol, use it strictly
for bursts of speed when needed. Most of the operations would then be carried
out as with a normal boat, using a diesel engine to charge batteries. However
while a conventional design would use the diesel as the primary engine
and the batteries for short periods of underwater power, in this case the
boat would run almost all the time on batteries in a low-speed cruise,
turning on the perhydrol during attacks. The diesel was now dedicated entirely
to charging the batteries, which it needed only three hours to do.
The result was the elektroboot, finalized in January 1943. Although
the design would remain a paper-tiger, it did look impressive indeed. When
underwater the Type XXI managed to run at 17 knots, faster than a Type
VII running full out on the surface and almost as fast as the ships attacking
her. For most of the trip it ran silent underwater on batteries, surfacing
only at night, and then only to Schnorkel depth. Weapons were likewise
upgraded, with automated systems allowing the torpedo tubes to be reloaded
in less than 1/4 the time, firing homing torpedoes that would attack on
their own. Even the interior was improved, it was much larger and fitted
with everything from showers to a meat refrigerator for long patrols.
The design was to be produced in two versions, primarily the Type XXI,
and smaller numbers of the smaller Type XXIII. Both they were much larger
and more difficult to build than the existing designs, the Type XXI taking
some 18 months. Work didn't really get started until 1944, and only small
numbers were ever built. In their few uses, the designs proved invincible,
trivially avoiding attacking ships and never even being seen by the patrol
The Battle of the Atlantic: Hitler's Gray Wolves of the Sea and the
Allies' Desperate Struggle to Defeat Them
, by Andrew Williams.