“Black May” – Biscay Bay in May 1943 Part II

As for new attacks on the Biscay bases, which the Admiralty’s earlier Memorandum advocated, the U-boats and their essential services were sheltered under impenetrable concrete, Harris reminded the Committee, and the 10,000 tons dropped recently on the bases at Lorient and St.-Nazaire had, as the Admiralty themselves conceded, no appreciable effect on U-boat operations. (Slessor, too, was critical of the bombing, at this stage, of the Biscay bases, “which was actually quite useless and resulted merely in spoiling several nice old French towns.”) Chief of the Air Staff Portal spoke up in support of “Bomber” Harris, as he was known in the Force, saying of the U.S. Navy and Admiralty proposals that he deprecated the transfer of any of Harris’s bombers to Bay patrols on the strength of “a theoretical calculation.”

But the Bay Offensive had its own determined champions, including First Lord of the Admiralty A. V. Alexander, who pointed out that “without the Bay Offensive we cannot hope to kill sufficient U-boats to get the upper hand in the Battle of the Atlantic, whilst on the other hand it is believed that we can with an adequately equipped Bay offensive sink sufficient U-boats to destroy their morale.” Alexander announced that the Admiralty had revised downward their estimate of the number of additional long-range bombers required: from 190 to 175 if the U-boats possessed new 10cm detection gear, to 55 if they did not. The First Lord reminded the Committee that the enemy could run but he could not hide: “He cannot withdraw from the Bay.” First Sea Lord Pound expressed his conviction that “the provision of additional aircraft in the Bay of Biscay [was] an absolute necessity and not a luxury in the anti-U-boat campaign.” And U.S. Admiral Stark said that unless the Allies got the better of the U-boat, “we should be in a bad way.” By increasing the Bay patrols, he submitted, “we should be able, for the first time, to carry out an all-out offensive against the U-boats.”

Of course, the Prime Minister had the last word, and it was not favorable to the Bay proponents. With only limited forces, he said, it was not possible to devote the maximum number of aircraft to every theater. The distribution must be commensurate with the results obtained, and so far air cover over menaced convoys, as argued by Slessor, and the bombing campaign against Germany, as argued by Harris, were the most productive theaters for the effort and resources invested. Granting that “even if the Bay of Biscay patrols resulted in sinking only three or four U-boats a month and did not reach the higher figures mentioned in some of the Papers, this must be regarded as a very important object,” Churchill decided that aircraft for that purpose could not be supplied by denuding the essential missions of Coastal and Bomber Commands. Taking a cue from Averell Harriman’s suggestion that the Chiefs of Staff in Washington might find it possible to divert aircraft from other allocations to the Bay, the Prime Minister charged the Air Ministry and the Admiralty with the responsibility for consulting on an estimate of the balance of requirements that might be communicated to the U.S. Government. Oddly, the only Committee member to have his nose put out of joint by these proceedings was Slessor, one of the winners in the debate. Displaying what had all the earmarks of a fit of pique, he railed at the Admiralty for blindsiding him with the Williams Plan and its request for 190 additional first-line heavies, “without discussing it first with the man most directly concerned, namely myself.” Thirteen years later, he was still annoyed, writing in his autobiography: “I only received my copy of the paper the day before it was down for discussion, and went immediately to the First Sea Lord to tell him that I strongly disagreed with this method of tackling the problem, which I described as slide-rule strategy of the worst kind.… ” Slessor took satisfaction from recording that, “The Admiralty paper met with very little luck in the U-boat Committee the next day, where I remember one light-hearted Minister saying, ‘C’est magnifique, mats ce n’est pas la guerre!”

On 4 April he submitted to the A.U. Committee a set of counterarguments to the Williams Plan, explaining in his memoirs that “nothing could be more dangerously misleading than to imagine that you can forecast the result of a battle or decide the weapons necessary to use in it, by doing sums.” He went on to aver that, “The most important factors in any battle are the human factors of leadership, morale, courage and skill, which cannot be reduced to any mathematical formula”; which human factors, the reader will remember, Captain Gilbert Roberts had insisted to Commander Gretton were no longer enough in the Battle of the Atlantic. Taking on Williams’s operations research directly, Slessor wrote: “Summarizing my objections to the principle of strategy by slide rule, I urged that the problem should be tackled from a less scientific but more practical angle.”

It is hard to imagine a more tortured position for Slessor to have taken. It was the very science of O.R.S. that had made his angles practical, a fact that he himself recognized by the close working relationship to O.R.S. that he forged straightaway upon becoming AOC-in-C in the preceding month, and by the very science (and “sums”) he employed at length in his own Paper before the A.U. Committee on the threatened convoy-Bay patrol option.

Furthermore, in denigrating slide-rule strategy in his autobiography, he seems to have forgotten that in the foreword he wrote to Professor Waddington’s 1946 book, O.R. in World War 2, he praised “strategy by slide-rule” by name, and acknowledged that “No one who knows the true facts can have any doubt that a great deal of the credit for what is perhaps still not generally recognised as the resounding victory it was, namely the Battle of the Bay and the defeat of the U-boat in 1943, is due to men like Blackett, Williams, Larnder, Baughan, Easterfield and Waddington himself.” Raushenbush’s name he seems not to have known, although the name appears prominently in the Stark Plan, where he is identified as its author, and that was the Plan whose calculations Slessor acknowledged to the A.U. Committee near the end of May, as will be seen, as having been vindicated by events in the Bay.

Slessor’s letter to the A.U. Committee of 4 April was not taken up by that body. Instead, during the days that followed, Slessor was persuaded to make a complete volte-face. It may have been the Air Ministry or the Admiralty, or both, whose heavy hand wrought this singular reversal—the record does not say—but when the time came for the A.U. Committee to petition the U.S. Joint Chiefs of Staff for additional longrange bombers for the Bay, it was Slessor who was tapped to draft the document. With the fervor of a convert, brought to his new faith by either conviction or thumbscrew, Slessor gave the case for the Bay Offensive its most striking language yet. Signed by him, First Sea Lord Pound, and Admiral Stark, the telegram to Washington read, in part:

The one place where we can always be certain of finding U-boats is the Bay. Setting aside the relatively small proportion that pass into the Atlantic North-about [from German ports], the Bay is the trunk of the Atlantic U-boat menace, the roots being in the Biscay ports and the branches spreading far and wide, to the North Atlantic convoys, to the Caribbean, to the Eastern seaboard of North America, and to the sea lanes where the faster merchant ships sail without escorts.… It is a strategic problem which can only be solved by an appropriate deployment of our joint resources, designed to concentrate the necessary force at the decisive point in the battlefield of the Atlantic. We are aware that the United States, like Great Britain, has not enough aircraft to meet in full their many commitments and to afford really adequate protection to the coastal shipping on their long coast lines. But if we strike a decisive blow at the trunk in the Bay, the branches will wither.

In their telegram the three signers called the Bay “second only to the convoy routes” as a strategic priority in the Battle of the Atlantic. They noted that 150 “first-line” aircraft were already engaged in the Bay Offensive, and that thirty to forty longand medium-range aircraft could be added to the force through recall of a Leigh Light squadron from Gibraltar, new construction, and borrowing. These new figures led to a revision of the number of additional aircraft needed. Hence, to make up the 260-aircraft requirement stipulated in both the Stark and Admiralty Plans, Coastal sought from the U.S. Joint Chiefs six squadrons totaling seventy-two long-range anti-submarine aircraft, drawn, the signers underscored, “from the forces already allocated [at the Atlantic Convoy Conference in Washington the previous month] to the Atlantic theatre.” At that conference the U.S. side predicted that 217 aircraft of suitable type and equipment, including 56 VLR, would be available “in excess of’ immediate Atlantic requirements.

It was important, the signers added, that the squadrons be made available “at the earliest opportunity” so as to take advantage of the period when the U-boats were without a 10-centimeter search receiver. (The A.U. Committee Minutes of their 14 April meeting, which contain a first draft of this communication, indicate that the Committee backed the four-month offensive proposed in the Stark Plan as against the twelve-month offensive proposed by the Admiralty.) The six squadrons would be accommodated at bases in southwest England. A reinforcement on that scale, the signers believed, “might well have results decisive to the issue of the Battle of the Atlantic.”

But Washington’s reception of the British telegram was cool. While sympathetic to the plans for an intensive operation in the Bay, the Joint Chiefs responded on 1 May, they had to report, regrettably, that the aircraft that they had predicted to be “in excess of” immediate requirements did not and would not in fact exist. The number of ASW aircraft cited in the document produced by the Convoy Conference, Admiral King explained, was based on figures “the origin and accuracy of which could not be entirely vouched for and which apparently had raised hopes as to the availability of aircraft which facts did not now warrant.” This reply, appearing so casually dismissive of a formal Allied agreement, caused understandable resentment in England, where a new telegram was drafted asking, if the numbers produced by the U.S. to the Convoy Conference were in error, would the U.S. kindly send the correct figures as quickly as possible?

Another and longer interval ensued before King and the other Joint Chiefs replied, in part because these matters were not exactly in the foreground of King’s interests at the time, since he was then engaged in one of the most contentious interservice rows of the war over the question, Who would control American anti-submarine air squadrons, the Navy or the Army Air Force Anti-Submarine Command? Slessor, who would personally observe these bitter turf battles during a visit to the States in June, said later: “The whole atmosphere in Washington was poisoned by inter-service jealousy and suspicion.”

On a belief that the reader would not want to be wearied by a recital here of that tedious tangle of disputes, which resulted in the Army’s withdrawal from anti-submarine work in the fall of the year, we shall leave that to the parti-pris literature and say simply that, try as Slessor did, he never succeeded in obtaining the seventy-two aircraft requested for the Bay; and it was not until October (!) that he could count any appreciable number of reinforcements from the American side. In that month Coastal had three U.S. Army and one U.S. Naval operational squadrons based at Dunkeswell in Devonshire and two U.S. Naval squadrons that were still working up at St Eval. But by October, it must be recognized, the planned Second Bay Offensive was over, having been waged by the aircraft that Coastal already had in hand, and the crisis of the U-boat war had passed.

Before the telegrams began passing between London and Washington, and Army and Navy air interests began crossing swords across the Potomac River (though invited by the Army’s War Department in 1942 to occupy all of the second floor and part of another in the newly erected Pentagon, an invitation that Secretary of the Navy Frank Knox readily accepted, the Navy Bureau Chiefs, not wanting to live cheek by jowl with the Army or Army Air Forces, objected strongly to moving there, and would not do so until 1948), Coastal had mounted another Bay trial, Operation Enclose II, which ran from dusk on the 5th to dawn on the 13th of April. With fewer aircraft (86) than were used in the first Enclose (115), but with three more L/L Catalinas of No. 210 Squadron, the operation was positioned over the same ribbon of sea as before and with the same deceptive 1.5-meter A.S.V. flooding at night.

During the period, twenty-five U-boats transited the ribbon (as against twenty-eight estimated). The total of 980 flying hours produced eleven sightings, more of them at night than in daylight for the first time, and four attacks, leading to the nighttime sinking of U-376 (Kptlt. Friedrich Marks) by L/L Wellington “C” of 172 Squadron, and damage to U-465 (Kptlt. Heinz Wolf) by Catalina “M” of 210 Squadron Fewer aircraft and fewer flight hours had produced the same results as those achieved by the original Enclose. And other U-boat crews, having affected narrow escapes, no doubt experienced what Raushenbush called “sheer funk.”

With the demonstration of higher efficiency in the repeat of Enclose, it was decided, even before that operation was concluded, to launch a full-scale, long-term intensive patrol over a larger ribbon between 8½° and 12° W under the code name Operation Derange. A total of 131 individual aircraft, all that were available at the moment, though well below the 260 considered necessary by Raushenbush and Williams, were committed to the new operation, which was to begin at dawn on 13 April and to continue “until further notice.” Included in that number were three new squadrons, a rocm. L/L Wellington squadron, No. 407, an ordinary Wellington squadron, No. 311, and a Whitley squadron, No. 612.

Up to the end of April, eighty-one U-boats crossed the Derange ribbon, either inbound or outbound, and during that period a total of 2,593 day and night flying hours resulted in thirty-six sightings and twenty-two attacks. The percentage of sightings made to hours flown represented no improvement over Enclose II. But one kill was made and two outbound boats were so badly damaged that they were forced to return to Brest and St.-Nazaire, respectively. The 10cm.-equipped Liberator “D” of 224 Sqdn. dropped six D/Cs on the previously damaged U-332 (Hüttemann) 25 seconds after she had dived, sinking her, northwest of Cape Ortegal, Spain, on the morning of the 29th. Damaged were U-366 (Kptlt. Hans Hornkohl), depth-charged by L/L Wellington “R” of 172 Sqdn. on the night of the 26th; and U-437 (Oblt.z.S. Hermann Lamby), depth-charged by L/L Wellington “H” of 172 on the night of the 29th.

The principal effect of the twenty-two Derange attacks in April, however, was to induce exasperation at BdU, where the Operations staff had grown weary of reports from Commanders during Enclose, Enclose II, and now Derange that despite their Fu.MB (Metox) gear, they were being surprised at night like deer in a car’s headlights. On 27 April, Admirals Donitz and Godt made a fateful decision, which they signaled to all Commanders. Standing War Order No. 483 was forthwith revised to require boats (1) to maintain maximum submergence at night through the Biscay transit area, and (2) to fight it out with aircraft on the surface in the daytime if surprised while charging batteries. This decision would lead to heavy U-boat losses during May and the summer months—twenty-six kills and seventeen U-boats damaged in ninety-seven days and nights—causing it to be called by historians “a major tactical error,” resulting from, as Slessor represented it, “the stupidity of the enemy.”

British aviation historian Alfred Price argues that in April only two out of a dozen anti-submarine squadrons in Air Vice Marshal Bromet’s No. 19 Group were fitted with both Leigh Light and 10-centimeter radar, and hence were not numerous enough to cause more than the loss of “a few U-boats to air attack without warning.” But in April the ratio of nighttime L/L-Iocm. hours flown inside the Enclose and Derange ribbons to nighttime hours flown by unequipped aircraft was 777 to 428, and L/L Wellingtons made seven night attacks without Metox warning between 26 and 29 April, resulting in two outbound U-boats seriously damaged, U-566 and U-437, which had to abort their departures.

No doubt this nighttime coverage got BdU’s attention, and the Dönitz/Godt duumvirate decided that placing their battery-charging boats on the surface at night under the sudden surveillance of searchlights was a more perilous course than was deploying them on the surface in daylight, when at least their lookouts had a reasonable chance of sighting the enemy’s approach in time to bring anti-aircraft armament to bear. They would then have both a warning and a defense, neither of which they had under the lights. Perhaps Dönitz and Godt were not as “stupid” as Slessor thought. They were simply wrong. If the plan was to surface during the daylight hours, then the U-boats should have been instructed to dive upon sighting aircraft. They did not have the firepower to fight back successfully. And one downside to maximum submergence, whether by day or by night, was greatly increased transit time, which translated into reduced opportunities to sink shipping.

In making the decision to spend the battery-charging hours on the surface in daylight, Dönitz and Godt likely were influenced by U-333’s flak success against a Wellington and U-338’s success in downing Halifax “B” of 502 Sqdn., both in March; and by U-79’s protracted machine-gun defense on 12 April that forced Liberator “M” of No. 86 Squadron to break off an attack—details of which BdU transmitted to all boats as an incentive. (Three L/L Wellingtons were unexplainedly lost in the Bay during April.) But these three successes, it turned out, were thin reeds on which to base so dangerous a general policy.

And so, on the cusp of May, the Battle of the Bay entered a phase that had not been predicted by either Raushenbush or Williams, a phase in which the secret use of 10-centimeter radar counted less than either boffin had anticipated, since the night had effectively been taken away from the equation.38 Though Bromet’s No. 19 Group maintained night patrols at about the same level from April through August, night sightings decreased sharply at the end of April and the battle from 1 May forward became mainly one of mano-a-mano combat in daylight, and let the metal fall where it may. The essential point that should not be lost here is: displaced by the German decision as the top-drawer weapon in the Bay, the Leigh-Lighters nonetheless had proved for a second time that they were the controlling threat. Even now, in a passive role as menace-in-being, by slowing the passage of U-boats through the Bay, they saved numerous merchant ships from torpedo-wrought deaths.

Bromet’s bombers were ready for this May battle. Based mostly in Devon, Cornwall, and South Wales, they had trained to near-perfect pitch, absorbing the lesson from O.R.S. in 1942 that it was not the weapon but the man that counted. And they had mastered the tactical doctrine long earned by O.R.S. calculations and combat experience. Foremost in anti-U-boat operations was sighting. Two lookouts, the doctrine held, must keep a continuous watch from ahead to 90° on either side of the aircraft, and to prevent errors through fatigue, they should be relieved every half hour.

An efficient A.S.V. watch must also be maintained, except that A.S.V. Mark II (metric) must not be used in daylight unless visibility was under three miles, or the aircraft was flying above heavy cloud, or the gear was required for navigational purposes. No restrictions were placed on A.S.V. Mark III (centimetric). To avoid eye fatigue, radar operators should be relieved every forty-five minutes. The optimum altitude for detecting and surprising a U-boat was judged to be 5,000 feet where there was no cloud or where cloud bases were above 5,000. When cloud density was not more than 5/Ioths and below 5,000, aircraft should patrol 500 to 1,000 feet above cloud tops. When clouds were more than 5/Ioths and below 5,000, aircraft should seek concealment by flying as near the cloud base as possible. When a sighting was made, altitude should be lost as quickly as possible in order to be no more than 300 to 500 feet off the deck when three-quarters of a mile to a mile from the target.

The pilot should make the decision as to whether flying an indirect course toward the target was required, either to provide time to get the bomb bay doors open (where aircraft were so equipped) or to avoid an increase of speed that would throw off the bomb intervalometer setting. (Squadron Leader Terence M. Bulloch, cited in chapter 3 for his successes—altogether in his career he would sight 28 U-boats, attack 19, sink 4, and severely damage 3, becoming the most decorated ASW pilot in Coastal—deviated from the rule of fast descent by stalking a sighted boat from cloud cover, and only when positioned to make an attack up or down the boat’s track at an angle of about 20° would he initiate his dive. Bulloch did not fly patrols in May, but spent the month instead testing a new rocket-propelled weapon, to be used in action for the first time on 23 May, at the Aircraft and Armament Experimental Establishment at Boscombe Down.)

During the final stage of the run-in, aircraft should descend to 50 feet and deliver their attack as nearly as possible along the track of the U-boat, taking their point of aim according to the following data:

(1) The time from the release of a depth charge from 50 feet to detonation at the shallow setting (25 feet) is approximately 5 seconds (2 seconds in the air and 3 in the water).

(2) If the U/Boat is in process of crash-diving, her speed will be approximately 6 knots (10 feet per second). Therefore, if the U/Boat is attacked while some part of the hull is visible, the centre of the stick should be aimed 5 x 10 = 50 feet ahead of the conning tower (or its estimated position) at the time of release.

(If the conning tower is itself in sight, however, at the time of release, it is desirable to make this the aiming point, although theoretically the stick will then fall 50 feet behind it.)

(3) If the U/Boat has dived before the depth charges are released, the stick must be aimed a certain distance ahead of the swirl, the apex of which is made by the foremost end of the conning tower. This distance is, of course, that run by the submarine between its final disappearance and the time of detonation of the depth charges. Assuming that the speed of the U/Boat is 6 knots, the distances are as follows:

Time of Submersion: Distance to aim to release of DC’s ahead of swirl

5 sees.    100 ft.

10 sees.  150 ft.

15 sees.  200 ft.

20 sees.  250 ft.

25 sees.  300 ft.

30 sees. 350 ft.

(4) If the periscope only is sighted, the speed of the U/Boat will probably be only about 2 knots, i.e., 3.4 feet per second, hence the stick should be aimed 5 x 3.4 = 17 feet ahead of the periscope at the time of release.

NOTE: An additional allowance must always be made for the underwater travel of the depth charges (40 feet).

If the U-boat had just submerged, the approximate length of its diving swirl (100 feet) could be used as a yardstick for estimating the distance ahead that D/Cs should enter the water. It was unlikely that a D/C attack would be successful, however, if the U-boat had been submerged for more than 30 seconds, in which case baiting tactics might be employed: In these maneuvers, the aircraft set course from the position of the swirl to a distance of at least 30 miles and remained outside that range for not less than 30 minutes; then it returned to the same position, taking advantage of cloud, sun, or weather conditions for concealment, in the expectation that the U-boat would have surfaced again. When a surfaced U-boat used its flak against the aircraft—most boats were then equipped with one 20mm cannon and several machine guns on the bridge—the decision on how to respond rested with the aircraft Captain, but the Tactical Instruction made it clear what was expected of him: “He must remember that the primary reason for his existence is, for the time being, to kill U/Boats and that a U/Boat on the surface presents a much better chance of a kill than one submerged.”

The point was made that a U-boat’s bridge made a very unstable gun platform in any kind of sea and particularly if the sea was beam-on, and that even a large aircraft properly handled and using its forward guns presented a fleeting, dangerous, and difficult target. Aircraft Captains should therefore press home their attacks against enemy fire, preferably from dead ahead, “making full use of the front guns to kill the U/Boat’s gun crews or at least to keep their heads down.” (The U-boats, for their part, were instructed when under attack to keep the aircraft on a stern bearing in order to present a small target—though, ironically, this helped the aircraft to drop a D/C straddle up track—and to use all available flak and machine gun fire simultaneously. When the aircraft began its final run in, the U-boat should initiate evasive maneuvers at maximum speed using full helm. In cases where a strong cross-wind was blowing, the U-boat’s avoiding action should be to windward in order to take advantage of the aircraft’s drift sideways.)