Black May (19 page)

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 6
1
°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 interception
¹³
—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 visibility 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.

At 1200 on 26 April, owing to changes unexpectedly introduced by Berlin in naval Enigma settings, GC&CS and the OIC Submarine Tracking Room abruptly ceased reading U-boat traffic, and would not read it again until the afternoon of 5 May, a critical period in ONS.5’s
westward voyage, since it was during those nine days of cryptographic intelligence blackout that Commander Gretton’s convoy would enter the longitudes where U-boat packs were known to be maneuvering in strength.
¹⁶
With what Rodger Winn called “no precise information,” the most that he and Patrick Beesly in the Submarine Tracking Room could tell CinCWA Admiral Horton after 26 April was that three U-boat groups were still thought to be “in the general area off Newfoundland.” As Winn wrote later, “Thus [where ONS.5 was concerned] it was not possible to attempt any evasive routing although the convoy had in the first place been routed as far north as possible to avoid U-boats.'
¹⁷
Three westbound convoys earlier in April, ON.178, ONS.3, and ONS.4, also had been routed north by the tip of Greenland, with small losses to the first two and none to the third.
¹⁸
Perhaps ONS.5 would be as lucky.