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Supplemental Table of Contents

3.1   U-Boat Offensive

3.2   Countermeasures to the U-boat
3.2.1 Convoys
3.2.2 Aircraft
3.2.3 Scientific and Technical
3.2.4 Sinking of U-boats

3.3   Survey of Results
3.3.1 From the U-boat Point of View
3.3.2 From the Allies Point of View

 

 

Chapter 3

 

THIRD PERIOD

START OF WOLF PACKS; END-TO-END ESCORT OF CONVOYS

APRIL 1941 — DECEMBER 1941

 
3.1  U-BOAT OFFENSIVE

THE FRUITSof the intensified German U-boat construction program, started late in 1939, were beginning to appear as the average number of U-boats at sea in the Atlantic steadily increased from about 18 in April 1941 lo about 36 in August 1941. The main features of U-boat tactics during this third period were the increasing use of wolf-pack attacks forced upon the Germans by the evasive routing of British convoys and the scarcity of experienced U-boat commanders.
  The outstanding successes achieved by escorts in the Northwestern Approaches during March 1941 produced the direct result that, in April, U-boats abandoned the method of close attack on the surface while antisubmarine escorts were in company. The U-boats continued their search for weak spots in the antisubmarine defenses by moving away from the vicinity of England, where air coverage was heavy, and extended their operations further westward where they could attack convoys before the antisubmarine escort had joined. There was also a southward movement of the U-boats with increased activity in the Azores and Freetown Areas.
  April opened somewhat disastrously with heavy attacks, started before the antisubmarine escort had joined, on Convoy SC 26. About five U-boats participated in these attacks, ten ships were sunk, and, in addition, the armed merchant cruiser ocean escort was damaged by a torpedo hit. One of the attacking U-boats was sunk after the antisubmarine escorts had joined. Towards the end of April, four ships were sunk from Convoy HX 121 as a result of the first submerged daylight attack by a pack of U-boats. The shipping losses to U-boats in April were about the same as in March, with 41 ships of 240,000 gross tons sunk. However, only about 30 per cent of the tonnage sunk by U-boats was in convoy in April as compared with 60 per cent in March. About 13 per cent of the tonntrge sunk by U-boats in April was sunk in		 the Azores Area and another 15 per cent in the Freetown Area.
  The total shipping losses, from all causes, amounted to 682,000 gross tons in April 1941, a higher figure than for any previous month in the war. This was due mainly to the heavy shipping losses to enemy aircraft, about 296,000 gross tons, most of these losses occurring in the Mediterranean in connection with the evacuation from Greece and Crete.
  As a result of the heavy attack on Convoy SC 26 at about 28° west longitude, the Iceland routing scheme was adopted earlier than was originally intended. Escorts were based on Iceland, making it possible to meet comovs where the escort from England had to leave, and then to escort the convoys out to about 35° west longitude, the escort there picking up an incoming convoy and then turning it over to an escort group from England. Sunderland and Hudson aircraft were also moved to Iceland to provide air coverage for convoys in waters which could not be covered by aircraft based on England.
  Obviously this considerable increase in the distance over which transatlantic convoys were escorted was only achieved at the expense of weaker individual escorts with each convoy. This was partly compensated by reinforcing the Western Approaches with Asdic-fitted minesweepers. It is equally clear that the use of Iceland necessitated a certain rigidity of routing and tended to make the location of convoys by U-boats and enemy aircraft a simpler business. Against this, the daylight hours in these northern latitudes were rapidly lengthening as the summer months approached and the U-boat danger in daylight was a lesser menace than at night.
  The upward trend in shipping losses to U-boats continued as 58 ships of 325,000 gross tons were sunk in May. Over half the losses occurred in the Freetown Area, where a group of about six U-boats sank 32 ships of 186,000 gross tons during the month. To meet the increased U-boat activity in that area, additional escorts were added to the Freetown forces and
 

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U-BOAT OFFENSIVE17
action was taken to divert all shipping from the Freetown Area, except those ships which must of necessity pass through those waters.
  Attacks on independents continued to increase as only about 20 per cent of the shipping sunk by U-boats in May was in convoy. In addition, the U-boats continued to move further westward and on May 20 located Convoy HX 126 at about 11° west longitude, before the antisubmarine escorts had joined. Eight ships were sunk before the convoy was forced to disperse. This attack forced iho adoption of complete transatlantic escort.
  It was felt that the considerable weakening in the number of escorts with a convoy must be accepted in order to provide some degree of protection throughout the voyage. Complete transatlantic escort was accomplished by basing escort forces in St. John's, Newfoundland, and escorting in stages from England, using Iceland as a refueling base. The Royal Canadian Navy cooperated in these measures by placing all available destroyers and corvettes at the service of the Newfoundland Escort Force. Canada had about 35 ships fitted for antisubmarine service at that time. The first escorts from St. John's sailed on May 31, 1941, and, as a natural sequence to this development, it was decided by the middle of June to escort the convoys all the way from Halifax. The long-endurance corvettes were to run all the way between Halifax and Iceland, with the destroyers being limited to St. John's.
  Areas of U-boat activity in June were further afield and wider spread than before, with reports of U-boats near Newfoundland and south of Greenland. Despite the magnitude of the elfort exerted, the shipping losses showed an improvement over May, with 57 ships of 296,000 gross tons being sunk by U-boats in June. Despite the increasing number of U-boats at sea, the losses were kept down by the efficiency of British countermeasurcs as five U-boats were sunk during June by surface craft. Losses in the Freetown Area were greatly reduced and the U-boats had difficulty in locating the transatlantic convoys.
  When they did finally locate Convoy HX 133 on June 23, the results must have been rather disappointing to the Germans, as only five ships were sunk at the cost of at least two U-boats sunk. This successful defense of this convoy was due in large measure to the fact that, when DF bearings indicated that HX 133 had been sighted by a U-boat, the escort was increased from one destroyer and three corvettes to two		 destroyers, one sloop, and ten corvettes. This was accomplished by taking the risk of stripping the escorts from two OB convoys within comparatively easy reach. Fortunately, one of these OB convoys escaped unscathed while the other suffered the loss of only one ship.
  On June 22, 1941, Germany invaded Russia and this seemed to end the threat of invasion of England for the time being. This released additional air and surface craft to help in the battle against the U-boats. In addition, German aircraft were diverted to the Eastern Front and attacks on shipping by aircraft were greatlv reduced during the last half of 1941.
  The average number of U-boats at sea continued to increase during July and August, but they had very little success as only about 23 ships of 90,000 gross tons were sunk in each of these months. This meant that the average U-boat at sea in the Atlantic was sinking less than one ship a month, a much lower rate than had been experienced in the past. In an endeavor to make the interception of shipping easier the U-boats withdrew to the eastward towards the end of July and concentrated in the waters west of Ireland and to the east of 25° west longitude. This placed them at a focal point of shipping where they could intercept both the East-West and the North-South convoys. However, the U-boats had no better luck there in August than they had in July. By this time, even the Gibraltar and Freetown convoys had more or less complete end-to-end escort. Towards the end of August, there were indications that the U-boats were resorting to long-range attacks on convoys, probably firing a browning salvo, and also to deliberate attacks on escorts. This policy of attacking escorts might have proved more profitable in the earlier days of the war, when the number of escorts with convoys was much smaller and when the general escort situation was much tighter.
  In addition to the defensive successes scored in August, this month was marked by one of the outstanding events of the U-boat war, the surrender of U-570 to a Hudson aircraft on August 27, 1941. U-570 left on her first cruise on August 24 and was at sea for only 74 hours before she surrendered. The U-boat came to the surface at 1030 on the 27th, the precise moment the Hudson from Squadron 269 was overhead. The U-boat tried to crash dive but the Hudson was too quick for her, diving from 500 feet to 100 feet, and dropping four depih charges. Captain Rahmlow, believing the U-boat more seriously damaged
 

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4SUBMERGED DAYLIGHT ATTACKS ON INDEPENDENTS
 

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Title5
 

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6Title
 

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SURVEY OF RESULTS 7

 

 

 

 

 

 

 

 


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