Black May

by Michael Gannon

  That brass hat came in December 1942 when he was advanced to command of Escort Group B7, based at Londonderry. There he embarked in the new twin-screw River class frigate Tay, while the destroyer assigned to him, the eleven year-old, 329-foot, D-class flotilla leader H.M.S. Duncan, was refitting in Tilbury docks prior to recom-missioning. The B7 Group had just come off a rough convoy engagement in which the Senior Officer Escort (SO) and his ship had been lost, but Gretton found his ships to be “in great heart.” Throughout January, February, and March, a period of expanding U-boat activity, he led them on cross-Atlantic passages that were, ironically, eventful for their lack of U-boat contacts. “For three months the group ran hard but had nothing to show for it but rust,” he wrote later. “We seemed always to steer clear of the wolf packs, which were then at the height of their success.”2

  Aboard Tay he had his first sea experience with an HF/DF set. The Type FH3 equipment could identify the general position of a U-boat transmitting to base or to another boat on a high-frequency wave band, even indicate whether the U-boat was near or far. More exact “fixing” of a U-boat’s position required the “cross-cut bearing” provided by a second HF/DF-equipped ship, as Duncan would be when recommissioned. Between sailings Gretton worked his officers and technical ratings hard at Londonderry’s asdic and depth charge trainers, radar and HF-DF detection simulators, and the new Night Escort Attack Teacher, where all ranks and ratings who manned detection and communications equipment, the plotting table, or the bridge received intensive and realistic attack drills in nighttime conditions. Time and again they practiced on land the tactical maneuvers they would have to carry out at sea, which bore such code names as Raspberry, Half-Raspberry, Observant, and Artichoke.

  Gretton was relentless in the conduct of these exercises and he was quite prepared to sack anyone who flagged in the effort. Among his Captains he had the reputation of an egotist but a gentleman, a hard man but a fair man. “Kindness to incompetents seldom provided a dividend,” he wrote after the war, “whereas severity invariably paid. As [German Field Marshal Erwin] Rommel said, ‘The best form of welfare is hard training.’ … But the sailor will never admit it.”3 Gretton had no need as yet to purge this group, however, and the men of B7 seemed to have welded into a tautly skilled team.

  Group B7 finally got its blooding in early April when it relieved a Canadian group escorting the fast (nine knots) Convoy HX.231 from New York to the United Kingdom. Entering the mid-Atlantic Air Gap on 4 April, B7 soon had more than enough U-boat contact to make up for its sterile months, as for over four days and nights it battled a pack of fourteen boats. Tay, commanded by Lieutenant-Commander Robert Evan Sherwood, R.N.R., made asdic contact with one of them, U-635, and sank her with a well-placed pattern of depth charges. Another boat, U-632, had been sunk earlier by a Liberator aircraft from Iceland. And U-294, badly damaged by depth charges, was forced to return to base. But six merchantmen were lost in the exchange: three in convoy and three stragglers.

  The first loss, that of the British motorship Shillong, was the worst for Gretton. Loaded with zinc concentrate and wheat in bulk, the 5,529-GRT vessel sank from view within two minutes of being torpedoed, casting her entire crew into the sea. On her search for the U-boat, Tay passed slowly through the bobbing survivors, their life jackets aglow with red lights. Gretton shouted encouragement to them, but knew that pursuing the U-boat was his most urgent duty, lest others be attacked, and that Tay must not lie hove to lest a torpedo remove her from the screen. But, as late as 1964, when he wrote about the men he left to die, he called the moment “my most painful memory of the war…. ”4

  Finally, a mist descended on the ocean swells and ruined the visibility of the U-boats. On 7 April aircraft roared overhead in great numbers. Eventually, landfall was made off the north coast of Ireland, and B7 reentered its home port at Londonderry. Ninety-five percent of the convoy had come through the pack battle unharmed, and B7 had acquitted itself well in its first real trial of pluck and mind. Gretton was pleased—except with the performance of Loosestrife, whose Captain, in his view, had not shaped up to standards, and whom he promptly replaced.

  Waiting for Gretton was the recommissioned Duncan, which not only gave him a destroyer to go with the frigate Tay, but also gave him a second HF/DF set (Type FH4), which made possible cross-cut bearings in combination with Tay’s FH3, which alone during HX.231 had proved “worth its weight in gold.”5 Duncan was also reequipped with the latest asdics, Type 271 10-centimeter radar, and radio transmitters and receivers. On deck she mounted two guns, two torpedoes, and the new forward-firing impact-fused “Hedgehog.” Extra depth charge stowage had been created. His complement of 175 officers and men was unknown and untried, however, and he immediately set them to work jousting with last war-type submarines in the Londonderry exercise area, except on those days when he was asked to review HX.231 with Admiral Horton (CinCWA) in Liverpool, address a large audience of officers on the same operation, and huddle with RAF Coastal Command pilots on how better surface and air escort cooperation might be promoted.

  Then came the date, long predetermined, for ONS.5.

  As he pulled alongside the Commodore’s ship, Rena, Gretton exchanged documents with Brook, whose orders had come from the Trade Division of the Admiralty, and advised him by loud-hailer of the disposition of his forces. Gretton stationed Duncan in the center behind Argon and formed up the rest of his force on the port bow, beam, and quarter, and on the starboard bow and quarter, with the tanker and rescue trawlers astern. The screen in place, Brook signaled his convoy to gather way on course 280°. Notwithstanding the confidence B7 had gained from HX.231, Gretton had every reason at this moment to be apprehensive. He was sailing northwestward into what forecasters told him was atrocious weather with gale-force winds. That meant that his convoy ships, light on the water because they were in ballast, would be buffeted about like so many champagne corks, and that would work havoc with stationkeeping, throw some ships out of control, and leave others stragglers. Maintaining seven and a half knots would be impossible under those conditions. Furthermore, their course, northwest to 61°45’N, 29°II‘W, a position east of Ivigtut on Greenland, and thence southwest along the Great Banks of Newfoundland, would engage his fleet with pack ice and bergs.

  Gretton knew that Western Approaches thought that the northern route was worth the hazard, since aircraft could provide cover south and to the west. Even so, while bombers could fly along much of his route from bases in Northern Ireland and Iceland, ONS.5 eventually would enter the Air Gap longitudes below Greenland that most of those aircraft could not reach. And that was where he assumed the majority of U-boats would be lurking. Were they perhaps already stationed directly athwart his course? Western Approaches had assured him that it had routed ONS.5 through waters that were least expected to be U-boat-infested. It may have informed him, furthermore—the surviving records do not say—that Admiral Donitz had a record number of boats at sea (27 on return passage) and that probably as many as 36 boats were formed into two operational patrol lines, Meise and Specht (Woodpecker), positioned along an arc 500 miles east of Newfoundland.

  It could not give him the source of these data because Gretton, like other commanders of his duty and rank, was not “indoctrinated,” that is, in the know about “Z,” or “Special Intelligence,” which was distributed through one-time pad ciphers to a tightly restricted list of recipients in the source-disguising form called “Ultra.” Nor could Western Approaches inform him that the German communications monitoring and cryptographic service, B-Dienst, had possibly discerned ONS.5’s course from decrypts of the Anglo-American Naval Cipher No. 3 (“Convoy Code”). If that was so, it is not known on exactly what day such information might have been communicated to BdU. B-Service messages to BdU no longer exist. Weekly summaries of B-Service information do exist, in the Bundesarchiv-Militararchiv in Freiburg im Breisgau, but the summary for the week of 19–25 April contains no mention of ONS.5. Decryptions of the convoy code were not
always current.

  An example of the time lag between interception and decryption is the mention of ONS.5 that occurs in the Weekly Summary of 10–16 May, which begins: “The Iceland detachment of ONS.5 consisting of at least three merchant ships [escorted by H.M.S. Vidette] was to leave port at 0715 hours on 23 April in order to rendezvous with the main body [of the convoy] during the daytime of 26 April…. ”6 Obviously, with such a delay this information had no operational value. The first mention of ONS.5 in the weekly summaries dates from 26 April-2 May, and relates to Third Escort Group (EG3), which will be considered below.

  The first week of the voyage went about as Gretton expected. There was the usual mechanical mishap. At 2200 on the first night, the Polish Modlin (3,569 GRT), beset by engine trouble, parted company with the eighth column and returned to the Clyde. At daybreak on the 23rd the weather worsened. High waves and strong winds forced numerous ships out of position. B7 busied itself chivvying stragglers back into line all that day and night. As much as he could, Duncan kept to the center column, No. 6, and maintained the convoy’s slow speed as a means of saving fuel, since the refitted destroyer had been improved in every way except in fuel consumption, for which she was notorious. Her daily consumption at slowest possible speed was 8 percent. At 1630 on the 24th, despite continued heavy seas, Duncan closed with British Lady in an attempt to top up his bunkers, but after the tanker discharged only two of her 600 tons the buoyant wire and rubber hose streamed astern parted, and Duncan had to withdraw and wait for calmer seas. Refueling from Argon was impossible, he discovered, except in mirror-flat water, since the positioning of the American oiler’s canvas hoses would require Duncan to come alongside—too dangerous a maneuver in high seas. The uselessness of Argons precious cargo was foreboding.

  Duncan and Tay made regular HF/DF sweeps for U-boats transmitting to BdU or to other boats, but heard nothing. Actually, there was a U-boat not far ahead on their course, but for some reason, still unclear, it had not made a transmission to BdU since sortieing from Kiel, Germany, on 15 April. B7 would not learn of its presence until later in the evening of the 24th, when the boat was attacked by Boeing Flying Fortress “D” of No. 206 Squadron based at Benbecula in the Outer Hebrides. RAF Flying Officer Robert Leonard Cowey was piloting eight miles northwest of ONS.5 on a plan devised by Coastal Command to give the convoy cover from the afternoon of the 24th to midnight on the 27th.

  At 1725 one of his crew sighted a fully surfaced U-boat ten miles distant. It was U-710, a newly commissioned Type VIIC, on her first war cruise, under an untried commander, Oblt.z.S. Dietrich von Carlowitz, who was probably unaware of the convoy’s proximity. Instead of alarm-diving at the appearance of Cowey’s aircraft, which was normal U-boat behavior, Carlowitz sent a crew to man the anti-aircraft guns on the platform aft the tower. Inaccurate tracers brushed by as Cowey dove the four-engine bomber to the deck and released a stick of six depth charges (D/Cs) that straddled the U-boat at right angles to her track. The brand-new bows heaved vertically from the explosions and the rear gunner watched the hull sink stern-down in a froth of debris. Cowey circled back and dropped another stick into the wreckage, after which he counted twenty-five survivors flailing in the water. There was nothing anyone could do for them. Low on fuel, and his home base closed in by weather, Cowey headed for Reykjavik.7

  For ONS.5, dawn broke on the 25th with the ocean surface in a state of upheaval. Commander Brook struggled to keep his ships in station as howling winds and fierce wave action forced numerous vessels out of line. Brook recorded: “Convoy making 2–3 knots, steering badly.”8 These conditions continued into the night when, at one point, Brook and Gretton could see seven different sets of “two red lights vertical” from ships that were Not Under Control. The inevitable happened, as Duncan signaled Western Approaches:DURING GALE LAST NIGHT NO. 93 BORNHOLM COLLIDED WITH NO. 104 berkel. both damaged. 104 IS CONTINUING BUT BORNHOLM LEFT UNESCORTED FOR REYKJAVIK AT 1400.9 The collision occurred at 2355 when the convoy was proceeding at no more than 2 knots on course 301°. Brook, who did not learn of the accident until the next morning, reported that Bornholm was holed in the Engine Room about 10 feet above the waterline. He commented that progress made against the stormy seas that night was so slight that the convoy was “to all intents and purposes hove-to.”10

  A moderate gale continued through the morning hours of the 26th, when all ships were sighted but scattered. B7 managed to whip in all but No. 81, Penhale, lead ship of column 8, which straggled astern so badly Gretton detached her to Reykjavik, escorted by Northern Spray. During the forenoon hours convoy speed was 3 knots. At 1400 Gretton was cheered by the arrival of the Iceland contingent—B/s second destroyer, H.M.S. Vidette, with the British Bosworth, the Norwegian Gudvor, and the empty U.S. naval tanker Sapelo—which had been homed to ONS.5’s position by HF/DF and an RAF PBY Catalina. Vidette gave Gretton a destroyer not only faster (25 knots) than Duncan but the twenty-five-year-old V&W (Long-Range Escorts) Class vessel also had “longer legs,” owing to the removal of one of her boilers and the installation in the vacated space of extra oil stowage. Vidette was equipped with asdic and Type 271 radar, though not with HF/DF; hence she could not join Duncan and Tay in acquiring cross-bearings on U-boat transmissions. Gretton continued to fret about Duncans ability to continue at sea. Unless the weather cleared, he signaled Western Approaches, he might have to separate and refuel in Greenland.11

  Fortunately, the seas subsided the following morning, long enough for Duncan to top up successfully from British Lady, completing the process at 1100. He was followed by Vidette and the corvette Loosestrife, while RAF Hudsons from Iceland provided cover overhead. Later that day Northern Spray rejoined the convoy. Gretton recorded his position as 61°25’N, 23°49'W, south of Reykjavik and due east of Cape Discord on Greenland. So far there had been no sightings or electronic detections of U-boats. Except for the boat sunk three days before by Fortress “D,” there seemed to be no boats around. If there were, perhaps they were concentrated on a mid-Atlantic convoy known to be on the reciprocal of the same northern course that swept the southern tip of Greenland: The heavily laden SC.128, which departed Halifax on 25 April for the United Kingdom, had been routed to pass north and west of the U-boat groups known to the OIC Tracking Room as of its sailing date.

  Between the 22nd and the 25th the Specht and Meise groups, together with new boats just arrived in the area, had been reshaped by BdU to form three Groups: Specht, Meise, and Amsel (Blackbird). The Specht line, with seventeen U-boats, ran from 54°15'N, 43°15'W to 51°15'N, 38°55'W. An augmented Meise line, with thirty boats, ran from 59°15'N, 32°36'W to 56°45'N, 28°12'W. The Amsel line, with eleven boats, ran from 54°51'N, 32°00'W to 53°45'N, 29°35'W.12 The BdU orders establishing these dispositions originated as part of a plan to catch westbound ONS.4, but that convoy arrived at New York safely and intact. Two other convoys on northern courses, SC.127 (departed Halifax 16 April) and ON.179 (departed Liverpool 18 April) successfully eluded the patrol lines, SC.127 being diverted to a more northerly course on the 26th after the order enlarging Meise was decrypted nearly fourteen hours after its interception13—and just under the wire, as will be shown below. Convoy ON.180 (departed Liverpool 24 April), which trailed ONS.5, similarly would evade the patrol lines. With the majority of U-boats in northern latitudes, two other U.K.-bound convoys that were at sea in this period, HX.235 and HX.236, were safely directed along southerly courses.

  Two entries in the BdU war diary for this period are significant for revealing German operational failures and intelligence misjudgments. The first entry, dated 25 April: An earlier eastbound convoy, HX.234, which sailed the northern route and made port in the U.K. with two ships sunk and one damaged, had been pursued for four days (21–25 April) by no fewer than nineteen boats. The investment of that much energy and time had yielded disproportionately small success. In explaining the failure, Admiral Donitz and Chief of Staff Godt enumerated unfavorable weather, particularly snow and fog; changing visib
ility conditions; the shortness of the nights on the northern route; strong air cover from Greenland and Iceland; and (cited twice) “the inexperience of the large number of new Commanders who were not equal to the situation.”14

  The second entry, dated 27 April: the BdU reflected on the fact that on the day before, convoy SC.127 had suddenly changed to a more northerly heading and had passed untouched through a temporary seam between Groups Meise and Specht, which at the moment were maneuvering to new positions. Furthermore, an intercepted American U-boat Situation Report revealed that the Allies knew exactly where the U-boat groups were deployed as well as their current movements, and had the capability to reroute convoys accordingly. How had the enemy gained such knowledge? The BdU answered: “This confirms, more than ever, the suspicion that the enemy has at his disposal a radar device especially effective in aircraft, which our boats are powerless to intercept.”15

  Of course, it is true that the Allies had 10-centimeter airborne radar, undetectable by any equipment with which the U-boats were then supplied, but its average range sweep was fifteen miles, hardly what would be required to descry the positions of even one wolfpack. Apparently Dönitz and Godt more readily believed in the existence of a (for then) preternatural eye in the sky that laid bare anything that moved across thousands of square miles of ocean than that Allied cryptographers had simply done what B-Dienst had done: cracked the other side’s cipher. That commonsense conclusion—a kind of Ockham’s Razor—never swayed BdU’s mind, and Dönitz himself obstinately refused to entertain the likelihood throughout the war and after it. (He similarly refused to believe at this time, as earlier noted, that the Allies possessed shipborne HF/DF capability.) But had he been aware that cryptographic intelligence was the source of the Allies’ uncanny knowledge, Dönitz would have been greatly encouraged by something else that happened on the day that SC.127 slipped past harm’s way: the Allied cryptographers went blind.