In March 1943, Grand Admiral Dönitz’
U-boats are on the attack – they sink 108 Allied vessels that month alone.
Allied officials are desperate, and some fear a German victory in the Atlantic
is imminent. If the Allies lose the Atlantic, Britain loses its lifeline – and maybe even the
war. But by May 1943, it will be the U-boats limping home in defeat. So how, in just two
months, did the U-boats go from hunters to hunted? From 1939, German U-boats threaten Allied
shipping. Although German surface raiders do play a role, Admiral Karl Dönitz hopes his
submarines can wage a so-called ‘tonnage war’ against British merchant vessels. This means
sinking enough merchant shipping to either massively degrade British military capabilities,
or better yet – force London to surrender. At first, the Germans have some success.
Dönitz calls summer 1940, “the happy time”, in which U-boats easily target mostly isolated
merchantmen, sinking 471. When the US joins the war in 1942, this increases to 1,160. The
U-boat crews' term this the “second happy time” or even “American Shooting Season”.
For British Prime Minister Winston Churchill, the Atlantic is the critical theatre
on which all others depend, and by late 1942 it is one of the few areas in which
Germany remains decisively on the offensive. In November 1942, U-boats alone sink 768,000 gross
tons of Allied shipping, their peak for the entire war. As a result, Churchill asks his allies for
more assistance. He also lays down new guidelines for referring to the German submarine threat:
“Enemy submarines are to be called U-boats. The term “submarine” is to be reserved
for Allied underwater vessels. U-boats are those dastardly villains who sink our
ships, while submarines are those gallant and noble craft which sink theirs.” (Gannon)
At the Allied Casablanca conference in January 1943, US leaders agree to prioritise the
Atlantic and delay the invasion of France and Germany until 1944 . Although some commanders
accept reluctantly, others understand it is impossible to use the United Kingdom as a base
for invasion with a lingering U-boat threat. But even with promises of more US support, issues remain. Across the allied
effort there is significant demand and internal competition for scant resources.
Meanwhile, Dönitz has more U-boats than ever. In 1939, Dönitz had just 39 subs, but by early
1943 he has around 300 and more are being build. Then, when Grand Admiral Erich Raeder’s resigns
as Navy Commander-in-Chief in January 1943, Hitler promotes Dönitz to the top naval position . Hitler
tells Dönitz to maintain the pressure in the Atlantic, although the admiral remains realistic
about the challenge in a radio broadcast: “The harsh realities of the submarine
war [means that] even more difficult times lie ahead of us.” (Van der Vat 289)
With a submariner in command of the entire German navy, the Allies also expect the U-boat menace to
grow. One area of concern is the Mid-Atlantic Air Gap, a favoured U-boat hunting ground known to
allied seamen as “Torpedo Junction”. By 1943, partly thanks the massive expansion of the
Royal Canadian Navy, Allied warships can provide end-to-end escort, but they’re still too few and
remain vulnerable without air support. Airbases in the UK, Iceland, US and Canada have been
improving coverage, but there’s still a gap of up to 1,000-km gap off the Cape of Farewell. Allied
commanders try to close it with escort carriers – including retrofitted civilian vessels – or
Very Long-Range bombers like the B-24 Liberator, but until January 1943, British Coastal Command
only has 6 VLR Liberators. The majority go to the bomber offensive against Germany or the Pacific.
Meanwhile, in December 1941, the German navy’s Beobachtungsdienst intelligence service cracked
the British Naval Cipher No. 3. By intercepting British communications, they organise group
attacks on convoys. U-boats locate about 70% of convoys thanks to codebreaking.
Allied resources are also drained by the 1942 Operation Torch landings in North
Africa, and the Battle for Tunisia in early 1943. The Royal Navy diverts 125 destroyers
and other escort ships to Torch, while fuel demands for African operations mean North Atlantic
convoys have less fuel to out-manoeuvre U-boats. The result is an increase in sinkings
in early 1943. In March alone, German U-boats and surface ships sink 120
Allied ships globally, totalling 704,000 tons – 484,000 of which sinks in the Atlantic.
This rapid increase in tonnage sunk – 74% over the previous month – is often seen as a major
crisis. A March 1943 British memorandum claimed: “...[T]here is insufficient shipping to allow
us to develop the offensives against the enemy, which have been decided on. Every ship sunk makes
the situation worse... We can no longer rely on evading the U-boat packs and, hence, we shall have
to fight the convoys through them.” (Haslop 210) A December 1943 Allied report even goes so far to
suggest victory in the Atlantic – and therefore the entire war - was threatened.
More recent research though, has questioned the crisis idea. The supposed
March crisis mostly focuses on two convoys, which suffer disproportionate losses – 22 of
90 merchant vessels sunk. Overall, however, only 31% of March convoys are attacked, much lower
than the 52% attacked in November 1942. In fact, in the first quarter of 1943, sinkings are
lower than any 1942 quarter. The allies are also building more ships than they are losing, with a
net gain of 2 million gross tons by March 1943. Perhaps most significantly, there is nothing in
German sources which portrays March as a moment of imminent victory. In fact, within two months,
the U-boats withdraw from the Atlantic in defeat. Just as the March convoy battles are raging, the
Allies meet in the Atlantic Convoy Conference to better pool resources and standardise
procedures. The top priority is closing the mid-Atlantic Air Gap and taking the fight
to the U-boats. The Commander-in-Chief of the Western Approaches is optimistic:
“I really have hopes now that we can turn from the defensive to another and
better role – killing them.” (Redford 74) Early 1943 also sees several tactical,
technological and military developments all coming to fruition around the same time. Ultra
intelligence, from the cracked German Enigma is the most well-known tool available
to the Allies, but it was by no means the only one – or even the most important.
Ultra can provide a general location of most U-boats, which are tracked by the men and women in
London’s Submarine Tracking Room . Convoys reroute around them – an effective tactic. But Ultra
intelligence is slow, and sometimes it takes up to 72 hours to de-crypt German communications. There
are also periodic blackouts when Germans alter their settings – including almost all of 1942.
And, as the number of U-boats at sea increases, the likelihood of evading them decreases. Ultra
is vital as a wider strategic tool but cannot pinpoint U-boats preparing to attack.
That’s where other technology comes in. By early 1943, more allied escorts are equipped
with better sonar and radar equipment. Underwater ASDIC sonar can listen for submerged U-boats,
gauging range and bearing. Not only does this reveal approaching U-boats, but allows for
more accurate use of anti-submarine weapons, like the Hedgehog and depth charges.
Meanwhile, ships and aircraft equipped with the new 10-centimetre radar can detect U-boats
on the surface. None of these tools are perfect, but when combined with others, they create
a near impenetrable network of defences: “The first indication of a U-boat attack would
be from the ASDIC people who would pick up a contact... you could hear these pings... and the
difference between the ping and the pong is the distance how far the submarine is away. When they
think they’re right over the top of the submarine, the order is ‘Fire’. That means the depth-charges
go... A colossal volume of water would come up... it was almost like lightning going
across the water. In daytime it’s a fantastic thing to see.” (Bailey 67/68)
German submariner Anton Staller aboard U-188 is on the receiving end of a
depth charge attack in March 1943: “Alarm bells shrilled loudly... “Destroyer
on the starboard bow... Range about 5,000 meters!”... A quick glance at the manometer
showed me that we were at 100 meters, at the same instant for the first time I heard
ahead of us the roar of exploding depth charges. Now I discovered how appalling loud these sounded
under water. Though fearful I concentrated on my hydrophone wondering if I would ever hear
anything again in my life... ” (Willman 49) Another important Allied development is High
Frequency/Direction Finding, known as HF/DF or “Huff Duff”. This can detect German U-boat
radio communications out to 25 kilometres, close enough to pursue and attack. It greatly
outranges surface radar and helps allow escorts to be more proactive. The technology existed
since 1942, but in 1943 it’s much more available, with at least 2 HF/DF equipped ships per convoy.
With this comes more powerful anti-submarine weapons and better organisation. Previously 6
escorts were considered adequate to protect 24 merchantmen, but civilian experts led by Professor
P. M. S. Blackett, find that eight escorts can protect 48 merchant ships just as effectively.
This combines smaller convoys into larger ones and frees up escorts which can become mobile support
groups assisting specific convoys under attack. And finally, there are more Very Long-Range
bombers and escort carriers. By May, Coastal Command has 49 VLR bombers, up
from 17 in February. Although dwarfed by the hundreds of bombers attacking German
industry, this number is enough to close the air gap. Aircraft like B-24 Liberators, Whitley
bombers and Sunderland and Catalina Flying boats, become vital submarine killers, quickly
accounting for around half of U-boat losses. The combination of new tools and tactics
is devasting to the U-boat fleet. In April, the battle balances out, as the Allies
lose 39 merchantmen but sink 15 U-boats. May 1943 is the decisive month, especially the
voyage of convoy SC-130. Heading to Liverpool from Halifax, Nova Scotia, the convoy has 37
merchantmen and 8 escorts, several equipped with High Frequency Direction Finding and new
10-cm radar. German naval intelligence identifies the convoy and gathers up to 25 U-boats in three
wolfpacks to attack to attack. Donau 1 and 2 approach from the south-east, while Wolfpack
Iller is already in the area. The plan is to attack the convoy in the airgap, but British
Ultra intelligence is aware of this. However, a system failure means the information is not
passed to the escort commander. Even so, when the attack opens on May 18, the escorts proactive
sweep for the U-boats and spoil their attacks, while the convoy also makes evasive turns. Soon
the battle moves within the range of approaching Allied aircraft which hound the U-Boats
and force them to submerge. By May 21st, U-boat command abandons the attack.
The Allies sink three U-boats and damage another with no losses. On board one of the sunken
U-boats - U-954 – is Admiral Dönitz youngest son, Paul, who dies with the rest of his crew.
The SC-130 battle is the pinnacle of a terrible month for the Kriegsmarine, in which
they lose a total of 41 U-boats – almost 25% those operational . Kapitänleutnant Peter-Erich Cremer
at U-Boat Staff Headquarters later recalled: “This May situation was quite out of hand: as I
was soon to learn, the number of boats that failed to return from patrol reached... more than one a
day, and there was talk of “Black May”.” (Gannon) On May 24, Dönitz orders his U-boats to
withdraw from the Atlantic until better equipment and countermeasures are available.
So why did things go so wrong, so fast for the U-boats? Allied developments are one factor,
but there were also German weaknesses. Firstly, the Germans had poor intelligence on Allied
capabilities, especially High Frequency Direction Finding, radar, and Enigma decryption. As
a result, submariners didn’t know how to avoid or compensate for them. Secondly, Dönitz’s
top-down approach required constant radio reports, especially before an attack . This gave British
Ultra and HF/DF detection more chances of locating them. During the SC-130 battle, there were 104
HF/DF reports, allowing the Allies to pinpoint the U-boats. Thirdly, the Kriegsmarine lacked
reliable air cover. Dönitz demanded more from Hermann Göring’s Luftwaffe, but Göring resisted
diverting resources away from his own interests. The increase in U-boat numbers also didn’t
mean a proportionate increase in sinkings, although the sheer number of active
U-boats still worried the Allies: “By April 1943 the average kill per U-boat at sea
had sunk to 2,000 tons. This might be interesting as a sort of sporting score, but the number of
U-boats operating had so greatly increased that it was of little significance in solving the problem.
When Daniel Boone, who shot fifty bears a year, was replaced by fifty hunters who averaged one
each, the bears saw no occasion to celebrate the decline in human marksmanship.” (Van der Vat 316)
But individual U-boat performance and crew experience, were dropping quickly. In
1940, U-boat commanders had on average two years' experience. In 1943 this was only
8 months. Most U-boat captains killed in May 1943 had only one or two patrols to their name.
In 1940, 2% of U-boat captains were responsible for 30% of sinkings. All these so-called “aces”
had entered the Kriegsmarine before 1935, but by 1943, the veterans of the early war were
gone. Roughly 850 U-boats – about 75% of the total built and crewed during the war – would never
damage an Allied merchantman. In November 1940, the average tonnage sunk per U-Boat per day
was 430 tonnes. In January 1943, it was 65. From 1939 to early ‘43, the Atlantic is the
only theatre in which Germany successfully maintained the offensive. But now even there,
they are in retreat. Dönitz’s withdrawal is not meant to be permanent though. He fast-tracks new
U-boat developments and shifts back to a smaller group tactics, but the U-boat wolfpacks
never make a meaningful return. Instead, the Atlantic becomes the logistical
highway for the Allied invasion of Europe. Two years after “Black May” for the German U-Boat
fleet, Admiral Dönitz becomes Head of State and Supreme Commander of the Armed Forces of Nazi
Germany. After, that is, Adolf Hitler and Joseph Goebbels commit suicide in the Reichschancellery
bunker as the Red Army is closing in on the city centre during the climax of the Battle of
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