refers to a period (May 1943) in the
Battle of the
campaign during World War
, when the German
) (UBW) suffered high casualties with fewer
Allied ships sunk; it is considered a turning point in the Battle
of the Atlantic.
Black May was the culmination of the period of crisis in the Battle
of the Atlantic, which occurred between March and May 1943.
March had seen the U-boat offensive reach its peak, with a series
of major convoy battles, first around convoys HX 238, and SC 121;
then followed the battle for HX229/SC122
, the largest convoy battle
of the war.
Allied losses for March totalled 120 ships, of 693,000 tons of
which 82 (476,000 tons) were lost in the Atlantic. The UBW lost 12
U-boats during this time.
A Royal Navy report later concluded “ The Germans never came so
near to disrupting communications between the New World and the Old
as in the first twenty days of March 1943” ,.
April saw some respite for the allies, as UBW was unable to
maintain such a large presence in the Atlantic in April. Many of
the boats heavily involved in March had withdrawn for replenishing;
nevertheless the boats still operational in the month remained
active.A particular shock at the end of April was the attack by
U-515 on convoy TS.37, which saw the loss of 4 tankers in 3
minutes, and another 3 over the next 6 hours.
Allied losses in April were 64 ships totalling 345,000 tons; 39
ships (235,000 tons) were lost in the Atlantic.UBW lost 15 boats
from all causes.
However the following month saw the strategic and tactical
advantage swing to the allies, where it remained for the rest of
May opened with the battle for ONS 5
hard-fought clash which saw heavy losses on both sides; 12 ships
were lost for the loss of 6 U-boats.But the tactical improvements
of the escorts began to take effect;The next three convoys attacked
saw 7 ships sunk, for the loss of 7 U-boats.Finally, SC 130, saw 5
U-boats sunk, without loss to the convoy.
Shaken by this, Adm Doenitz ordered a retreat from the Atlantic, in
order to recoup; the U-boats were unable to return to the fray in
significant numbers 'til the Autumn, and never regained the
Total allied losses in May were 58 ships of 299,000 tons of which
34 ships (134,000 tons ) were lost in the Atlantic.
May 1943 saw the U-boat strength reach its peak, with 240
operational U-boats of which 118 were at sea, yet the sinking of
allied ships continued to decline. May 1943 also saw the greatest
losses suffered by U-boats up to that time, with 41 being destroyed
in May 1943 — 25% of the operational U-boats.
On 24 May 1943 Karl Dönitz
, shocked at the defeat suffered
by the U-boats, ordered a temporary halt to the U-boat campaign;
most were withdrawn from operational service.
May had seen a drop in allied losses coupled with a disastrous rise
in U-boat losses;18 boats were lost in convoy battles in the
Atlantic in the month,14 were lost to air patrols; 6 of these in
the Bay of Biscay.With losses in other theatres, accident, or other
causes the total loss to the U-boat arm in May was 43 boats.
|Cause of Loss
|Ship + Shore-Based Aircraft
|Ship + Ship-Based Aircraft
(Raised and Re-commissioned)
This was the worst month for losses suffered by UBW in the war so
far, nearly 3 times the loss in the previous worst month, and more
boats than had been lost in the whole of 1941.Equally significant
was the loss of experienced crews, particularly the junior officers
who represented the next generation of commanders.Black May
signalled a decline from which UBW never recovered; Despite various
efforts over the next two years the U-boats were never able to
re-establish the threat to allied shipping they had posed..
This change was the result of a combination of the sheer numbers of
allied ships at sea, allied air power at sea, and technological
developments in anti-submarine warfare.These had been introduced
over the period; these came to fruition in May, with devastating
Tactical and technical developments
The first and most important factor in the allied success was that
the escorts were getting better; escort groups were becoming more
skilled, and scientific analysis was producing more efficient
tactics.New weapons such as the Hedgehog
, and FIDO
, were coming into use; and new
tactics, such as the creeping attack pioneered by Capt."Johnnie" Walker
devastatingly effective.Support groups were organized, to be
stationed at sea in order to reinforce convoys under attack, and to
have the freedom to pursue U-boats to destruction, rather than just
drive them away.The advantage conferred by ULTRA
, conversely, became less significant at this
stage of the campaign. Its value previously had been to enable
convoys to be re-routed away from trouble; now that the escorts
could successfully repel or destroy attackers there was little
reason to do so.Whilst the Admiralty
baulked at using convoys as bait, out of regard for Merchant Navy
morale, nonetheless there was no
advantage in avoiding U-boat attacks.
Over convoys, the introduction of "Very Long Range" aircraft and
to close the air gap
had a major effect in both repelling assaults and destroying
U-boats.The re-introduction of air patrols over the
Biscay, to attack boats as they came and went from base,
also began to take effect at this stage of the
was used here too, to improve the efficiency both of
attack methods and the weapons in use.
Numbers were a factor in allied success, though the effect was more
than sheer numbers alone; both UBW and the Allies had many more
vessels operational in 1943 than they had at the beginning of the
The Atlantic campaign was a Tonnage war
UBW needed to sink ships faster than they could be replaced to win,
and needed to build more U-boats than were lost in order not to
lose.Before May 1943 UBW wasn’t winning; even in the worst months,
the majority of convoys arrived without being attacked, whilst even
in those that were attacked, the majority of ships got through. In
HX.229/SC.122, for example, nearly 80% of the ships arrived
safely.At the start of the campaign UBW needed to sink 700,000 tons
per month to win; this was seldom achieved. Once the huge
shipbuilding capacity of the United States came into play, this
target leapt to 1.3 million tons per month.What changed in May was
that UBW started to lose, which continued till the end of the
The Germans tried to turn the campaign in the Atlantic back in
their favour by introducing tactical and technological changes.
tactical change saw U-boats starting operations in new waters, such
as the Indian
Ocean, in the hope that their targets would be less
Although the U-boats found fewer escort ships,
there were also fewer merchant ships to sink (the majority of ships
were of British India
called the Monsun Gruppe
Another tactical change was to try to counter allied air power by
fighting on the surface rather than diving.When U-333
came under attack from an aircraft in
March 1943, rather than diving, she stayed on the surface and shot
down the attacking aircraft. It was hoped that this success could
be repeated if U-boats were given better anti-aircraft
To facilitate this several U-boats converted to flak U-boats
), but proved unsuccessful. At
first, this gave the Allies a shock but they soon welcomed attempts
by U-boats to prolong their surface stay. Additional defences
against aircraft was offset by the U-boat having to remain on the
surface longer, increasing the chance of the submarine's pressure
hull being punctured. The gunners' effectiveness was limited by the
lack of protection from strafing aircraft, and Allied pilots often
called in surface reinforcements to deal with such flak boats.
Furthermore, the extra anti-aircraft guns caused drag when the
U-boat was submerged. The U-333 incident had proved to be the
exception rather than the rule and the flak experiment was
abandoned after six months; the best defence for U-boats against
aircraft was to dive if attacked.
New technologies were also seen as a way to regain the advantage.In
mid-1943, two new technologies were introduced to the U-boats: the
warning device and T5 Zaunkönig
The Wanze warning device was designed to give U-boats advanced
warning of aircraft in the hope U-boats could dive before the
aircraft started its attack run. The T5 Zaunkönig torpedoes were
designed to zigzag in the hope that they would have a better chance
of finding a target within a convoy.
The first Schnorkel
which went into service in August 1943, utilized the Schnorkel
extendable breathing tube which allowed the U-boat's diesel engines
to run submerged for longer periods. However, the Schnorkel
suffered from technical problems and did not see wide use until
UBW also experimented with radical new submarine designs, such as
the Walther Elektroboot
and Type XXIII
None of the new tactics or technologies could reverse the tide of
war for the U-boat arm and heavy losses of U-boats continued. After
May 1943, the rate of loss of U-boats was greater than the rate at
which new U-boats were commissioned, and the number of operational
U-boats slowly declined.
- Miller, David. U-Boats: the Illustrated History of the
Raiders of the Deep. Washington: Brassey’s Inc, 2000.
- Stern, Robert C. U-Boats in action. Squadron/Signal
- Stephen Roskill : The War at Sea
1939-1945 Vol II (1956). ISBN (none)
- Dan van der Vat : The Atlantic Campaign (1988) ISBN 0 340 37751
- Axel Neistle : German U-Boat Losses during World War II (1998).
ISBN 1 85367 352 8