From the top of the white and gale-whipped lighthouse on the Isle of Orsay, a twenty-four-hectare slab of grass-ruffled rock that peeks from the Hebridean sea, the keeper could just make out the ships beginning to gather. The sky was a sheet of grey. High and cold winds thrashed at the ocean which, even this close to land, heaved to form great dips and peaks, aftershocks of the storms a few miles out to sea. Most of the forty-two merchant ships that chaotically assembled during the afternoon of Wednesday 21st April 1943 were in ballast, their bellies ready to be filled with supplies of food and fuel that Britain so desperately needed when, all being well, they arrived on the North American coast in a couple of weeks’ time.
Every one of the ships that formed convoy ONS.5 (Outbound to North America, Slow), or MARFLEET as it was code-named, had sailed in convoy before. Two–the American McKeesport and the British Dolius–had even survived a savaging by U-boats just a few weeks earlier. Still, experience only went so far; in this menacing weather, maintaining a tidy position in the convoy was impossible. In sight of the forsaken Scottish coastline, the boats tossed like toys in a toddler’s bathtub, caught rhythmically in the brushing beam of the lighthouse.
The ‘Slow’ in the convoy’s designation was apt; at best ONS.5 could travel at just seven and a half knots. Anyone watching the sea that day knew that, if the weather endured, there was little chance it would manage even this easy pace on the journey ahead. The convoy’s chosen route would take them into some of the worst weather of the decade, through waters thick with ice. This passage, to the far north, had been chosen to minimise the risk of encountering U-boats; earlier that month three convoys had taken the same route, two of which sustained only small losses, the third making it through untouched.* The chosen course would provide the convoy with air support from nearby coastlines. Still, at the centre point of its journey, the ships would be forced to cross the notorious Gap, where, three years earlier, the City of Benares had been sunk and where, thanks to the deadly weather, there would be no air support to ward off attackers.
The British were unaware that ONS.5’s route was already known to German intelligence, who had successfully intercepted their communications. At the height of his powers, and now, finally, with a sufficient number of U-boats to deploy his wolfpack strategy to its fullest, Grand Admiral Doenitz was poised for battle. In the days that followed, he would dispatch the greatest wolfpack ever assembled to attack a single convoy, one that would eventually consist of five times as many U-boats as escort ships. The odds against survival were great; ignorance may not have been bliss, but it at least allowed the convoy to set sail toward a battlefield from which anyone in possession of the facts would surely have fled.
Even before the ships left sight of the Isle of Orsay’s lighthouse, as many as thirty-six U-boats sat between the convoy and its destination.1 They had been placed following a ‘thorough examination’2 of recent convoy routes and organised by Doenitz into two operational patrol lines, positioned into a great arc across the Atlantic, 500 miles east of Newfoundland. As if to conceal their menace, each wolfpack was named after a bird: one Specht (Woodpecker), the other Meise (Chickadee).
The atmosphere on the convoy ships was muted and fretful. Everyone involved knew that the forthcoming journey across the Atlantic Ocean was going to be long, cold and brutal. Nobody, on either the German or British side, could have known that by the time the first ships to survive the journey spied the North American coastline, the outcome of the Battle of the Atlantic would have been settled via a long and arduous conflict: the Battle of Birds and Wolves.
At 14:00 on Thursday 22nd April, Commander Peter Gretton, graduate of WATU and captain of HMS Duncan, arrived on the scene. Gretton, leader of the convoy’s bodyguards, escort group B7, came flanked by an entourage of fighting ships, the frigate Tay and the corvettes Loosestrife, Sunflower, Snowflake and Pink. The naval ships, sheepdogs to the merchant flock, comprised a modest force to protect a convoy of such immodest size, but the crews were as well rehearsed as any before them.
Gretton, who with captains Walker and Macintyre formed the trio of Liverpool’s greatest U-boat hunters, had a reputation for being a ruthless master. He wouldn’t hesitate to cut loose anyone he considered to be a weak link. ‘Kindness to incompetents seldom provides a dividend,’ he later wrote, ‘whereas severity invariably pays.’* His assiduousness had meant the ships under his charge had spent the last few weeks training and drilling off the coast of Ireland. At WATU, Gretton had seen first-hand, via The Game, the benefit when escorts worked as a close-knit team rather than a collection of autonomous individuals. He later described Roberts’ work as ‘invaluable’ not only thanks to the ‘invention of new search schemes for finding U-boats’ but also in the way the game ‘helped to weld groups together’.3 Roberts had made a number of ‘very stupid officers really think’, Gretton wrote, ‘sometimes for the first time in their lives’, and Gretton had fully absorbed the lessons he learned at WATU.
When he arrived in Londonderry, Gretton endlessly drilled his ships in the WATU-coined operations Raspberry, Half-Raspberry, Observant and Artichoke, each of which would play a key role in the coming journey.4 These exercises had gone, as Gretton put it, ‘rather better than usual’. Despite the disparity between the huge size of ONS.5 and the rather meagre contingent of ships that comprised Gretton’s escort, he believed his team was fully prepared to meet the challenge posed by any waiting U-boats.
For many of the captains under Gretton’s charge, the U-boat threat had been experienced not only through WATU’s game, but in person at sea. Harold Chesterman, a powerful lieutenant with Hollywood looks, had been present two years earlier at the sinking of the SS Aguila, when the twenty-one Wrens and a naval nursing Sister died. Four days later Chesterman’s ship HMS Zinnia, one of the Aguila’s escorts, was herself torpedoed during the same action. Her magazine exploded, and she sank in twenty seconds.
As Chesterman clung, fingers bleeding, to a slowly disintegrating smoke-float in water lumpen with bodies and wreckage, he came to the decision to give up the fight and, rather than prolong his pain, embrace the water. A few feet down, Chesterman, who was twenty-four years old, saw a vision of his young wife, Caroline, begging him to reconsider. He fought his way back up and regained purchase on his float, determined that if he was going to die, it would be by necessity, not choice.5
In the first light of the morning, coughing up blood and oil, he was hauled from the water by a rescuer. Sixty-eight members of Zinnia’s crew perished that night. Chesterman and his captain, Monsarrat’s close friend Charles Cuthbertson,* were among just seventeen survivors–‘shrunken hostages of the sea’, as Monsarrat described them.6 The two men continued to serve together aboard HMS Snowflake until, when Cuthbertson was due to move on, he broke protocol by recommending that the young lieutenant assume command of his ship. Chesterman became the youngest officer to command a major war vessel, and a much-valued member of Gretton’s crack team of escort ships.
Despite the adverse weather, Gretton was in high spirits, and not only thanks to a robust belief in the skill of his escorts and the experience of his captains. While attending WATU he had taken one of the game-playing Wrens, Judy Du Vivier, to dinner just before she had been sent to Londonderry. A forlorn Du Vivier bade goodbye to the striking escort commander, not knowing if she would ever see him again. Shortly thereafter, Gretton learned that he too was to be stationed in Londonderry. Thirty years old and eager to ‘get better acquainted’ with this striking young woman, he wasted no time in arranging a second date.
When the pair next met on 2nd January 1943, the first time they had seen one another since their time together in Liverpool, Du Vivier explained how she had recently recovered from a bout of pneumonia. She was young and fit, she said, but the illness had been serious enough that she had been sent to a medical facility where doctors from the Royal Army Medical Corps had nursed her back to health. This brush with mortality–combined with the persistent advances toward her, as Gretton put it,7 by male members of the British submarine service and Canadian navy stationed at Londonderry–had convinced the young, jut-jawed commander to act. Du Vivier accepted his proposal. The church was booked for the end of May. Now Gretton simply had to make it across the Atlantic Ocean twice: once to collect supplies, and then back home to deliver them in time for his appointment at the altar in five weeks. The safe and timely passage of convoy ONS.5 was, then, of both national and personal importance.
Gretton pulled alongside the convoy’s commodore ship, the Rena, and over a loudhailer finalised plans for the coming journey with its commodore, J. Kenneth Brook, shepherd to the convoy flock. With everything in place, the commodore gave the order for the convoy ships to move into formation. By the time the forty-three merchant ships that comprised ONS.5 had left the British coastline, headed towards Greenland, the light was beginning to fail.
Gretton’s destroyer was a notoriously thirsty vessel whose tanks would be empty after a fortnight at sea. In order to save fuel during the relatively safe first leg of the journey, he positioned her in the middle of the convoy behind the tanker Argon, one of two fuel ships ready to top up, via hoses, any ships that ran low along the way.
On the second day, Gretton attempted to refuel the Duncan, but the waves were too severe. The hose was plucked from its socket by the tugging force of the sea. Gretton realised that without calmer waters it would be impossible to refill from either tanker. There was no respite from the wind and waves. On 25th April 1943 the weather was so tempestuous that the ships, many of which had been knocked out of formation, were only able to progress at two knots,8 a quarter of the speed at which they might sail in fine weather. Visibility was so poor that even at this crawl, two merchant ships collided, leaving one, the Bornholm, with a hole in the engine room.
The next day Gretton signalled Horton at Derby House to say that unless the weather cleared to enable his ship to refuel, he would have to separate from the convoy in order to make an impromptu stop in Greenland.9
‘On the one hand… I did not want to leave my group at such a time,’ Gretton wrote. ‘On the other… I did not like the idea of running out of fuel altogether and having to be towed, possibly at a very inconvenient phase of the operation.’10
Meanwhile Doenitz, receiving reports of convoy sightings, added a third patrol line, Amsel (Blackbird), to his assembled ranks of wolves. The combined total of this force was formidable. Woodpecker contained seventeen U-boats, while Chickadee, to which Doenitz had added more units between the 22nd and 25th April, now had thirty. The new patrol, Blackbird, consisted of eleven U-boats, bringing the number of German vessels ready to intercept any crossing convoy to close to sixty.
In what would be one of the only moments of respite in the journey, the weather cleared shortly after Gretton sent his message to Derby House, and a few hours later the Duncan successfully refuelled.
At midday on 26th April, just as Gretton and ONS.5 entered the longitudes where the wolfpacks were assembled, the Germans made changes to the naval Enigma code settings that scrambled the messages sent between BdU, the U-boat headquarters, and the U-boats. In England, the Government Code and Cypher School, which intercepted and decoded these German messages, was abruptly blinded, unable to read the signals that, for months, had alerted ships to the whereabouts of U-boats and their plans.
Without precise information, the best that the Submarine Tracking Room in London could tell Horton, who was attempting to direct ONS.5 from his office at Derby House, was that the three U-boat groups were ‘in the general area off Newfoundland’.11 This blindness meant that nobody in the Royal Navy, least of all Gretton, knew that on 27th April, sixteen new U-boats had been instructed by BdU to assemble into a fourth wolfpack, Gruppe Star (Starling), east of Greenland, directly across the convoy’s path.
The German war diary, written on 27th April, made clear the target of all this activity: ‘The object of [Starling] is the interception of the next ONS convoy at present proceeding in the North… A slow south-west-bound convoy is expected there on 28 April.’12 BdU’s estimate was correct. At 09:00 on the 28th, even before Starling had properly assumed its formation, the lookout in the conning tower of U-650 spotted a thatch of mastheads on the horizon, belonging to the ships of ONS.5.
U-650’s captain, Ernst von Witzendorff, signalled the sighting to Doenitz and Godt and, as he had been taught, began trailing the convoy, writing: ‘I am closing them to see what we have.’ For Doenitz, the stage was set for what would surely be a successful action. At 10:43, BdU sent a message ordering all sixteen U-boats within Starling to ‘attack on basis of Witzendorff’s report’. One of the subsequent messages that passed between the U-boats was picked up by convoy ships Duncan and Tay, who used their ship-mounted huff-duff sets–direction-finding equipment that enabled any two boats fitted with the contraptions to identify the source of a high-frequency radio transmission, and thereby pinpoint a U-boat–to estimate the hunter’s position.
Aware that the convoy was being shadowed, Gretton dispatched Chesterman’s ship, Snowflake, to investigate, while simultaneously altering the convoy’s course thirty-five degrees to starboard. Snowflake found nothing. The weather again closed in and the wind began to blow ‘like the bells of hell’, as Gretton later wrote in his report. As visibility shrank to just three miles Gretton quietly fretted that the U-boat may have been just one member of a much larger pack. Then, in the early evening, Duncan picked up a U-boat close on the port bow. He made chase, ordering Tay to make a parallel search to port. Forty minutes later Duncan’s bridge spotted a telltale cloud of spray, where the waves had struck a U-boat conning tower.
As Duncan approached, the U-boat dived. After dropping a pattern of ten depth charges, Gretton and Robert Sherwood, captain of Tay, executed the first WATU operation of the journey, Observant, a search of the area in a square shape, each ‘side’ two miles long, with the U-boat’s last known position at its centre.
As the weather worked against the convoy, so too it worked against the U-boats. Despite Gretton’s fear that the convoy was currently surrounded by a flock of attackers, only four of Starling’s U-boats had managed to rally to U-650. It was enough to unsettle Gretton. That evening, he listened in dismay as each member of the wolfpack made its evening report to BdU. The sound on the huff-duff was, as one report put it, like ‘a chattering of magpies’. Darkness fell and with it the likelihood of an attack rose.
The air escort that ONS.5 had enjoyed from 24th April had been discontinued at midnight on the 27th, since, up until that point, there had been no Admiralty reports of U-boats in the vicinity. For now, Gretton and his handful of escort ships would face the U-boats alone.
‘The night,’ as Gretton wrote, ‘promised to be a busy one.’13
In Derby House, from his eagle’s-eye office Horton studied the huge map on the wall opposite, with its concentration of ships and, thanks to Gretton’s reports during the past few hours, U-boats clustered south of Iceland. It was clear that ONS.5 desperately needed support. Horton scanned the plot for possible back-up, and his eye fell on HMS Oribi, crewed by the newly engaged John Lamb, fiancé to Christian Oldham.
Lamb’s ship was a member of the newly formed support groups, a rather plain name for highly trained, quick-moving flotillas that were sent into the Atlantic with the express purpose of providing impromptu assistance wherever it was required. The support group would, essentially, loiter in the ocean, waiting to be dispatched to the nearest emergency. The Oribi was currently escorting the convoy SC.127, en route from Sydney to Halifax. Horton estimated that it could be spared and, if it made good time, could be with Gretton within a day or two.
The idea for these elite naval groups was devised months earlier by Sir Percy Noble, but he never had control of a sufficient number of spare ships to implement the plan. When Horton took over from Noble, he was equally convinced that this kind of flexible, hard-punching force would be decisive in the Battle of the Atlantic. On his first day at Derby House, Horton wrote to the Admiralty to press the ‘urgent need’ for these support groups. His appeal was rejected: there simply weren’t enough quick-footed warships available.
Horton changed tack. He reasoned that since convoys still had to cross the Gap in the middle of the Atlantic unaccompanied, why not reduce the number of ships in the escorts either side of the area by one, and form the spare ships into support groups that could operate with more flexibility inside the Gap? After all, this was the only area of the ocean where the U-boats could still act with impunity and so represented the most perilous leg of the journey for the convoys. Again, the Admiralty denied Horton’s suggestion.
In March 1943, as the battle between the U-boats and the Allied escorts was in crescendo, 1,120 merchant seamen, escort sailors and passengers were killed in just four battles against U-boats. Two thirds of the 110 Allied ships lost to U-boats that month were travelling in escort. In Derby House, where the mood was bleak, Horton reasoned that the losses were not the result of failings in the tactics devised by Roberts and the Wrens, but by the simple fact that the number of escort ships protecting the convoys was no longer sufficient in the face of such devastatingly large wolfpacks.
Horton needed evidence to take to London to prove that the support groups he was petitioning for would have diminished the losses of the past month. Once again, it was the results of a wargame that substantiated his claim.
On 15th March, four weeks before ONS.5 gathered at the Isle of Orsay, the Wrens had plotted on the main wall at Derby House the progress of two real convoys, HX.229 and SC.112, each headed toward three wolfpacks totalling thirty-eight U-boats. Concurrently, one of Roberts’ colleagues, Captain Neville Lake, added three fictional support groups to the wall, shadowing the real convoys.
Lake hoped to estimate what effect such reinforcements might have on the looming battle. He populated his support groups with markers to represent real warships that were currently under construction, or nearing operational capability, and used his ghost escorts to support the real convoys, fending off wolfpacks while the battle played out in almost real time on the map. As well as adhering to the current weather conditions, Lake took into account fuel consumption and the depletion of depth charges to ensure that his exercise, overlaid on the real battle, was as accurate as possible.
Although many of the Wrens forced to play out Lake’s game while simultaneously trying to plot the real battle were frustrated (they described it as ‘Lake’s folly’14), the final results were clear and, for Horton, conclusive. At the end of the battle for HX.229 and SC.112, which German radio reported as ‘Die grösste Geleitzugschlacht aller Zeiten’–‘the greatest convoy battle of all time’15–twenty-one Allied ships lay on the ocean floor. Lake estimated that, had his fictional support groups been real, at least eight ships would have been saved.
A few days later Horton was summoned to London for a meeting with Churchill and other high-ranking members of the Anti-U-Boat Committee. Lake hurriedly wrote up his notes from the game and handed the docket to his commander-in-chief, just as Horton was leaving to board the night train from Liverpool to London.
At the meeting the following day, Churchill was in a dark mood. Oil stocks were below danger levels and, as he put it, the U-boats were once again threatening the prosecution of the war.
‘What are you going to do about it?’ Churchill bluntly demanded of Horton.
‘Give me fifteen destroyers and we shall beat the U-boats,’ Horton replied.16
Churchill banged his fist on the table.
‘You admirals are always asking for more and more ships,’ he said. ‘When you get them, things get no better.’
The prime minister’s outburst was forgivable; assets in any war, on any side, are always finite. The miserable task of a leader is to balance the scales in order to achieve equipoise between a rising number of needs and a diminishing allocation of resources. Choosing his moment, Horton slid Lake’s wargame report across the table. Churchill glanced at it, then looked more carefully. Finally, he adjourned the meeting so that he and Admiral Harold Stark, commander of US naval forces in Europe, could study it in more detail. When Churchill reconvened the meeting, he looked up from the docket at Horton.
‘You can have your fifteen destroyers,’ he said.
When he returned to Liverpool, Horton told Lake that he ‘had never admired the prime minister more than in that moment’. Horton later described how Lake’s game achieved what two admirals had been unable to do in years of trying. Western Approaches finally had its support groups.
By the final week of March 1943, Churchill had made good on his promise: Horton had more than twenty new destroyers at his disposal, which he divided into five support groups ready to dash to wherever assistance was required.
As first lieutenant of HMS Oribi, John Lamb was a crew member on the third of these five elite support groups. It was an intimidating role. For the past three years, escort crews would cross the ocean hoping to avoid any and all contact with U-boats. Lamb was one of the first sailors to charge into the Atlantic with the express aim of hunting the hunters. Action was inevitable. And so it came.
Seven days after the Oribi left port, the ship received a signal from Horton ordering it to detach from its current escort, and make its way, at an urgent speed of twenty knots, to assist Gretton and the weather-beaten boats of ONS.5. In Belfast Castle, Christian Oldham watched her fiancé’s ship break away from the safety of its convoy, and begin to make its way across the plot, toward the needle-bed of freshly pinned U-boat markers.
The atmosphere at Derby House was doubly muted. While everyone was aware of the massing of U-boats in the Atlantic, tragedy had already arrived at the bunker. Three nights earlier, on 25th April, a signal arrived, probably from ONS.5, that required an alteration to the main plot. At that moment, Patricia Lane, a young member of the Women’s Auxiliary Air Force, was teetering high on the ladder used by the young women to reach the pins and string. The ladders could be slid, at speed, parallel to the map via tramline tracks at the top and bottom.
‘One quickly got used to them and acquired a splendid balance, seeing how far the elastic would stretch when putting up the convoy routes,’ wrote Mary Carlisle, a Wren who routinely worked the plot. (Like June Duncan, Carlisle had also cheated her way past the medical into the Wrens; while Carlisle benefited from a photographic memory, she was burdened with poor eyesight. Fearing she might fail to read the alphabet from the far wall during her eye test, Carlisle learned the position of the letters on the standardised test card in advance.17)
Patricia Lane, however, was less experienced than the Wrens, as the WAAF only climbed the ladder once a day, at midnight, to chalk up flight schedules for the next day’s convoys. When the signal came in, one of the Wrens grabbed the ladder, and pushed it eastward to the trouble spot on the plot. Patricia lost her balance, slipped and fell onto the hard floor. She was whisked out of the plotting room and taken to a nearby hospital, where she later died of her injuries. The Wren who had grasped the ladder was taken off the watch in shock, but as the threat to ONS.5 continued to build, the work had to continue. Since Patricia had died while serving at a secret headquarters, her death was unreported. As a result of the tragedy, all Wrens were made to wear a safety harness (‘a positive nuisance’, according to Mary Hall) while working on the main plot at Derby House.
While the majority of the action the Wrens faced was experienced at a distant remove through the micro-drama of maps and tokens, death would at times more closely touch their world. Elsie Pearsal, who had worked for an income-tax office prior to the war, joined the Wrens as a cook, for ‘a change of pace.’
‘I had come straight from income tax,’ she said. ‘I didn’t know how to boil an egg.’18
Pearsal was sent to Blundellsands hotel in Liverpool, where she cooked for the Wrens working at Derby House. The ingredient list from which the cooks had to improvise ambitious meals was impoverished: dried tomatoes, onion and apple. The Wrens would fill great metal pans with water and stir and stir the mixture to make suet pudding.
‘It took two Wrens to pour the mixture, which smelled of petrol,’ she recalled.
Once cooked, the Wrens would carry the food from the hotel along the street to two Victorian houses, where those stationed in Derby House would come to eat. On one occasion Pearsal and another Wren were struggling to manoeuvre a great and cumbersome pan of vegetable soup into one of the houses. As they made it through the front door, Pearsal considered saluting the quarterdeck, then, feeling the slop of the heavy pan, decided against it. Moments later a Wren officer walked into the hallway.
‘Without thinking my hand shot up,’ Pearsal recalled. ‘Peas and carrots went all over the thick floor mat by the entrance. I was eighteen years old.’
Pearsal and the other young Wren cooks would exercise on the beach each day. In formation, they would pass through Waterloo, on the Mersey, and from the bridge see the ships in Gladstone Dock. On the beach the Wrens would march and exercise under instruction. One morning they were turned away and told there would be no drills that day.
‘We later found out that the previous night a ship had been mined and overnight bits of bodies had swept onto the beach,’ she said.
Rumours of the washed-up bits of body on the beach, like the news of Patricia Lane’s death in the plotting room, spread quickly through the Wrens. Each provided a reminder, in its grim and respective way, of the risks and stakes, direct and indirect, to their work.
On 29th April, four days after Patricia Lane’s death, Gretton received news that his escort was to be joined by Lamb’s ship the Oribi, and four other vessels from the third support group, currently en route from Iceland.19
Gretton’s prediction that the previous night would be a busy one had proved correct: the Duncan had detected and seen off four separate U-boat advances, in a tempestuous sea where even the simple act of reloading the depth charges was a life-threatening endeavour. No ship in the convoy had been sunk or damaged. Two of the U-boats involved in the attacks, U-386 and U-528, had been so severely damaged by depth charges that they had been forced to withdraw to base. Despite the success, Gretton remained nervous. The Oribi and its sister ship, HMS Offa, were still hours away, and the weather had worsened to an ‘astonishing’ degree, by Gretton’s appraisal, ‘even for the North Atlantic’.*
Frustrated at the previous night’s failure, on the morning of 29th April, Kapitänleutnant Wilhelm von Mässenhausen of U-258 slipped inside the convoy, using the technique pioneered by Kretschmer, and sat at periscope depth starboard of the convoy’s fourth column. Somehow the U-boat evaded the ASDIC sweeps of the patrolling escort ships, allowing von Mässenhausen to successfully fire at the American freighter, McKeesport.
An alarm bell woke Gretton, sleeping after the night’s work, and, at 07:30, one minute after the torpedo struck, he ordered the next WATU-coined manoeuvre of the journey: Artichoke. As one destroyer powered at maximum ASDIC speed toward the wounded ship, all others in the escort turned outward and performed a fifteen-knot sweep in line. U-258 managed to slip away. The McKeesport, listing to one side, managed to maintain convoy speed for almost fifty minutes while taking water, before the order was finally given to abandon ship at 08:15. The sixty-eight men on board were picked up by the crew of the Northern Gem, one of the two rescue ships attached to B7 Group to pick up survivors of U-boat attacks. One man, a Swede called John Anderson, later died of exposure, the only fatality of the day.
The Oribi joined the escort in the early hours of 30th April, and there were no more attacks on the convoy. By mid-morning the weather had eased enough that Lamb’s ship was able to refuel. It was the first time that the Oribi had attempted to do so at sea and, as a gale again whipped up, the inexperienced crew botched the job.
‘She made such a mess of the oiler’s gear that no one else could refuel that day,’ Gretton wrote of a snag that was to have life-altering consequences for the commander of ONS.5’s escorts. A cluster of U-boats continued to shadow the convoy but, as the storm returned once again, blown in by a force-ten gale, none of them dared surface to mount an attack, even though their targets were static and strewn.
‘Although the engines were turning, we were just sitting there stationary’, said Howard Goldsmith, leading sick-berth attendant on Chesterman’s Snowflake.20
The wretchedness of the situation is captured in Commodore Brook’s logbook, where he wrote: ‘Half convoy not under command, hove to and very scattered.’
As soon as Gretton had alerted Derby House of the wolfpack, the Admiralty had ordered renewed air cover to provide ONS.5 with some support. Despite the atrocious conditions, aircraft continued to make fly-bys throughout the day. Some signalled the position of icebergs, and of straggling ships. One American bomber forgot to switch off its navigation lights, an oversight that worked in the convoy’s favour when the globe-like, flashing beacons caught the attention of U-381, which sent a frenzied signal to Doenitz reporting a sky-borne secret weapon, ‘a light like a planet, that went off and on’.21
The combination of extreme weather and aircraft support precluded any action between the U-boats and the escort ships. Then, after an uneventful day, on 2nd May the storm eased, giving Gretton, his escorts and a Liberator from the Reykjavik squadron opportunity to round up stragglers and gather the flock back into formation. The convoy was now far enough north that ice, not waves, presented the gravest danger. Duncan again attempted to refuel, but the need for the tethered ships to wend around icebergs frustrated the manoeuvre.
The weather forecast for the coming days was dire. Gretton calculated that he now had only enough oil to make Newfoundland at modest speed. The exertion of action involving U-boats could empty the Duncan’s fuel tanks before it reached land and force the destroyer into the ignoble position of having to be towed to the North American coast, further endangering the ships it was supposed to be protecting.
After ‘much heart-searching’, Gretton made the decision to leave ONS.5. At 16:00, he passed command of escort group B7 to Lieutenant Commander Robert Sherwood, the highly experienced, thick-bearded and roughly spoken captain of HMS Tay.
‘We were most depressed,’ Gretton later recalled.22 WATU had invented the tactics and Gretton had drawn up the game plan, but now Sherwood would be the one to execute it.
Duncan wasn’t the only destroyer that had to leave ONS.5 due to fuel depletion that day. Three other members of the support group were similarly detached from the convoy, and Sherwood signalled Derby House to say that if weather conditions didn’t improve to allow refuelling, Offa and Oribi would be the next to go. Surrounded by ice and, having entered the Greenland air gap, now sailing under skies empty of air support, Convoy ONS.5 proceeded through the night with a woefully diminished force of protectors. As the merchant ships entered the most perilous leg of the journey, just three of its former seven-strong posse of bodyguard destroyers remained.
At Derby House, recognising the convoy’s vulnerability, Max Horton ordered another support group consisting of five warships to ‘proceed at best speed’ to reinforce the exposed convoy. It would, however, be two days before these ships could reach ONS.5’s position.
Following his promotion, Doenitz had moved the U-boat headquarters from France to the Hotel am Steinplatz in Berlin, which had been furnished for the purpose, so that he could continue to keep a close hand in directing the sea war.23 From his position Doenitz saw that not only did he have a unique window of opportunity to strike, he also had unparalleled resources with which to execute a major attack.
Frustrated by the wolfpack’s failure to halt the convoy’s progress during the past week, he ordered Starling, which by now had lost some of the original U-boats, and gained a few replacements, to rendezvous with Woodpecker’s seventeen vessels.
At 18:00 on 3rd May 1943, BdU signalled to the wolfpacks a stern command that made Doenitz’s expectations clear: ‘DO NOT HOLD BACK. SOMETHING CAN AND MUST BE ACHIEVED WITH 31 BOATS.’
As Gretton and his ship, Duncan, departed the scene, he could not have known that, as he later put it, the story of what happened next would be ‘the most stirring of convoy history’.