refers to a period (May 1943) in the Battle of the Atlantic campaign during World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, when the German
The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...
U-boat arm (U-Bootwaffe
) suffered high casualties with fewer Allied ships sunk; it is considered a turning point in the Battle of the Atlantic.
After February battles around convoys SC 118
Convoy SC-118 was the 118th of the numbered series of World War II Slow Convoys of merchant ships from Sydney, Cape Breton Island to Liverpool.-Prelude:...
, ON 166, and UC 1, Black May was the culmination of the March thru May 1943 crisis in the Battle of the Atlantic.
March had seen the U-boat offensive reach its peak, with a series of major convoy battles, first around convoys HX 228
HX 228 was a North Atlantic convoy of the HX series which ran during the battle of the Atlantic in World War II. It was one of 4 convoy battles that occurred during the crisis month of March 1943 and is notable for seeing the loss of the Escort Group leader Cdr AA "Harry" Tait.-Prelude:HX 228 was...
, SC 121, and UGS 6; then followed the battle for HX229/SC122
The battle around convoys HX 229 and SC 122 occurred during March 1943 in the Battle of the Atlantic, and was the largest convoy battle of World War II. British merchant shipping was formed into convoys for protection against...
, the largest convoy battle of the war.
Allied losses for March totalled 120 ships of 693000 LT (704,122.7 t), of which 82 (476000 LT (483,639.8 t)) 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 Many of the boats heavily involved in March had withdrawn for replenishing; nevertheless the boats still operational in the month remained active.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 four tankers in three minutes, and another three over the next six hours.
Allied losses in April were 64 ships totalling 345000 LT (350,537.3 t); 39 ships (235000 LT (238,771.8 t)) 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 the campaign.
May opened with the battle for ONS 5
ONS 5 was a North Atlantic convoy during the battle of the Atlantic in World War II; the battle surrounding it in May 1943 is regarded as the turning point of the Atlantic campaign....
, a hard-fought clash which saw heavy losses on both sides; 12 ships were lost for the loss of six U-boats. But the tactical improvements of the escorts began to take effect;
The next three convoys attacked saw seven ships sunk, for the loss of seven U-boats.
Finally, convoy SC 130 saw five U-boats sunk (Admiral Dönitz's son Peter was among those lost aboard U-954
) without loss to the convoy.
Shaken by this, Admiral Dönitz ordered a retreat from the Atlantic, in order to recoup; the U-boats were unable to return to the fray in significant numbers until Autumn, and never regained the initiative.
Total allied losses in May were 58 ships of 299000 LT (303,799 t), of which 34 ships (134000 LT (136,150.7 t)) 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
Karl Dönitz was a German naval commander during World War II. He started his career in the German Navy during World War I. In 1918, while he was in command of , the submarine was sunk by British forces and Dönitz was taken prisoner...
— 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; six 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
|| Number lost
| Shore-based Aircraft
| Ship-based Aircraft
| Ship + Shore-Based Aircraft
| Ship + Ship-Based Aircraft
| Other Causes
| Bombing Raid
(Raised and Re-commissioned)
| Total Lost
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 results.
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
The Hedgehog was an anti-submarine weapon developed by the Royal Navy during World War II, that was deployed on convoy escort warships such as destroyers to supplement the depth charge. The weapon worked by firing a number of small spigot mortar bombs from spiked fittings...
, and FIDO
The Mark 24 Mine was a US air-dropped passive acoustic homing anti-submarine torpedo used during the Second World War against German and Japanese submarines. It entered service in March 1943 and continued in service with the US Navy until 1948...
, were coming into use; and new tactics, such as the creeping attack
The creeping attack was developed during the Battle of the Atlantic in World War II as an anti submarine measure.It was first used by 36 Escort Group of the Royal Navy after being developed by the groups commanding officer, Captain "Johnnie" Walker....
pioneered by Capt."Johnnie" Walker
Captain Frederic John Walker, CB, DSO and three Bars, RN was a British Royal Navy officer noted for his exploits during World War II...
, proved 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. While the Admiralty
The Admiralty was formerly the authority in the Kingdom of England, and later in the United Kingdom, responsible for the command of the Royal Navy...
baulked at using convoys as bait, out of regard for Merchant Navy
The Merchant Navy is the maritime register of the United Kingdom, and describes the seagoing commercial interests of UK-registered ships and their crews. Merchant Navy vessels fly the Red Ensign and are regulated by the Maritime and Coastguard Agency...
morale, nonetheless there was no advantage in avoiding U-boat attacks.
Over convoys, the introduction of "Very Long Range" aircraft and escort carriers 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 Bay of Biscay
The Bay of Biscay is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay, in the Spanish...
, to attack boats as they came and went from base, also began to take effect at this stage of the conflict. Operational analysis 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 war.
The Atlantic campaign was a Tonnage war
A tonnage war is a military strategy aimed at merchant shipping. The premise is that an enemy has only a finite number of ships, and a finite capacity to build replacements for them. The concept was made famous by U-boat commander Karl Dönitz, who wrote: The shipping of the enemy powers is one...
; 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 700000 LT (711,235 t) per month to win; this was seldom achieved. Once the huge shipbuilding capacity of the U.S. came into play, this target leapt to 13000000 LT (13,208,650 t) per month. What changed in May was that UBW started to lose, which continued till the end of the war.
The Germans tried to turn the campaign in the Atlantic back in their favour by introducing tactical and technological changes. The first tactical change saw U-boats starting operations in new waters, such as the Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, in the hope that their targets would be less defended. Although the U-boats found fewer escort ships, there were also fewer merchant ships to sink (the majority of ships were of British India). These were called the Monsun Gruppe
The Monsun Gruppe or Monsoon Group was a force of German U-boats that operated in the Pacific and Indian Oceans during World War II...
Another tactical change was to try to counter allied air power by fighting on the surface rather than diving. When U-333
German submarine U-333 was a Type VIIC U-boat of the German Kriegsmarine during World War II. The submarine was laid down on 11 March 1940 at the Nordseewerke yard at Emden, launched on 14 June 1941, and commissioned on 25 August 1941 under the command of Kapitänleutnant Peter-Erich Cremer...
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 defenses.
To facilitate this several U-boats converted to flak U-boats (such as U-441
German submarine U-441 was a Type VIIC U-boat of the German Kriegsmarine during World War II, which served for a short time as an anti-aircraft submarine under the designation U-flak 1....
), 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 Wanze
warning device and T5 Zaunkönig
torpedoes. 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
fitted U-boats, 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 mid-1944.
UBW also experimented with radical new submarine designs, such as the Walther Elektroboot
An elektroboot was the first submarine designed to operate entirely submerged, rather than as submersibles that could submerge as a temporary means to escape detection or launch an attack.- History :...
(the Type XXI
Type XXI U-boats, also known as "Elektroboote", were the first submarines designed to operate primarily submerged, rather than as surface ships that could submerge as a means to escape detection or launch an attack.-Description:...
and Type XXIII
German Type XXIII submarines were the first so-called elektroboats to become operational. They were small coastal submarines designed to operate in the shallow waters of the North Sea, Black Sea and Mediterranean Sea, where larger Type XXI Elektro boats were at risk in World War II. They were so...
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.