During the spring of 1942, the massive U-boat pens at the French Atlantic bases were completed and brought to peak efficiency. Owing to the diversion of U-boats to the Mediterranean and the Arctic and to delays in the arrival of new boats assigned to the Atlantic, there were ample berthing spaces and repair crews to accommodate promptly all boats in need of refit. Hence the home base turnaround time of many boats was sharply reduced. This development, plus the sailing of six new boats (three IXs, three VIIs) from Germany to the Atlantic force, enabled Dönitz in April to order the largest U-boat force yet to American waters: thirty-one boats—fourteen IXs and seventeen VIIs.
These thirty-one boats were to be resupplied, where necessary, by two U-tankers. These were Wilamowitz-Mollendorf’s U-459, which had sailed in March and was still on station in the mid-Atlantic, and the new Type XB minelayer,* U-116, commanded by thirty-six-year-old Werner von Schmidt, which, owing to the failure of the SMA (moored) mine, had been temporarily released to Dönitz. However, while U-116 was en route to the operational area on April 29, a Coastal Command Hudson depth-charged and damaged her near Rockall Bank and she was forced to abort to Lorient for repairs. This mishap delayed U-116’s deployment for twenty-two days, disrupting the planned resupply operations for the April boats.
The damage to U-116 was a direct result of intensified Coastal Command air patrols in the Bay of Biscay. These radar-equipped aircraft caught and damaged two other new boats sailing from Germany in April: the Type IX U-172, and the Type VII U-590. The last was hit by a Whitley of Squadron 502, piloted by Edward Cotton. Both were compelled to return to France for repairs, delaying their departures to May, thus reducing the total number of April boats that reached America waters to twenty-nine.
Of these twenty-nine, sixteen were Type VIIs, of which nine had made prior patrols to the Americas. Three were commanded by Ritterkreuz holders: Giinther Krech in U-558; Reinhard Suhren in U-564; and Gerhard Bigalk in U-751. Twelve of the sixteen were to refuel from the tanker U-459 while she was still on her maiden voyage or while she was on a hurriedly arranged second voyage in early June.
Dönitz assumed correctly that the easy times in American East Coast waters were coming to an end. The April VIIs were certain to confront intensified—perhaps even lethal—ASW measures, especially from airplanes. It was also likely that the Americans had finally initiated coastal convoying. If so, the VIIs were to find the hunting very difficult. It would not be prudent for U-boats to attack inshore convoys in the shallow waters of the continental shelf at any time, day or night. There were not enough VIIs to mount sustained night pack attacks against offshore convoys, assuming they could be found. Should conditions in coastal waters prove to be unfavorable as believed, Dönitz had plans for some VIIs to refuel at sea and patrol to the less well defended Gulf of Mexico and Caribbean Sea.
Reinhard Suhren in U-564, who wore Oak Leaves on his Ritterkreuz, was the first of the April VIIs to arrive. After refueling from U-459, he briefly overlapped Peter Cremer in U-333 in Florida waters, arriving in early May. Cruising close to shore in shallow waters from Cape Canaveral to Fort Lauderdale, in merely one week, May 3 to 9, Suhren attacked and claimed five ships sunk (including two big tankers) for 30,000 tons. However, two of these ships, the 9,800-ton British tanker Eclipse and the 3,500-ton American freighter Delisle, survived the torpedo hits and were towed into ports and repaired, reducing Suhren’s confirmed bag for the week to three ships sunk for 20,400 tons, including the 7,000-ton Panamanian tanker Lubrafol.
Probing farther south to Miami, on May 14 Suhren sank the neutral 4,000-ton Mexican tanker Potrero del Llano, named after Mexico’s once-great oil fields near Tampico. Suhren claimed the vessel was sailing blacked out and that there were armed escorts in her vicinity, making her a legitimate target. The Mexicans insisted the vessel had bright spotlights illuminating the Mexican flags painted on her sides. Whatever the truth of the matter, the Mexican government seized upon the incident to declare that as of May 22 a state of war was to exist with Germany. Thereupon, Dönitz advised the Atlantic boats that all Mexican ships were fair game and to beware of ASW measures in Mexican waters.
On that same day, May 14, the United States Navy initiated an organized merchant-ship coastal-convoy system to replace the ragged (but effective) Bucket Brigade, between Key West and Norfolk. The plan was to sail a forty-five-ship convoy, escorted by not less than five warships as well as land-based aircraft, nonstop in each direction every three days. The first convoy, KS 500 (Key West, Southbound) sailed from Norfolk on May 14. Its counterpart, KN 100 (Key West, Northbound) sailed on May 15. The schedules were arranged so that all ships passed Cape Hatteras in daylight with maximum available air cover. Although the value of dimouts and blackouts remained in question, some cities along the southern coastline cooperated by imposing them.
Cruising off the Florida Keys on May 17, with all torpedoes expended, Suhren in U-564 spotted what was probably a section of KS 500. He tracked “fourteen ships escorted by four destroyers” rounding Key West and going west into the Gulf of Mexico. He broke radio silence to convey this important intelligence to Dönitz, then he set a course for home, overclaiming an impressive six ships for 34,000 tons sunk. However, his confirmed score—four ships for 24,400 tons, plus damage to two others—was the best patrol of the April VIIs.
On the final leg of his patrol in the Bay of Biscay, Suhren confronted a new and formidable hazard. After eighteen months of R&D and bureaucratic delays, RAF Coastal Command had finally (on June 1) put in service the aircraft-mounted Leigh Light, designed to illuminate U-boats during the last mile of the approach, when ASV meter-wavelength radar was blind. As part of intensified ASW air patrols in the Bay of Biscay, five twin-engine Wellingtons of Coastal Command Squadron 172 had been fitted with these lights.
While Suhren was approaching the French coast on the night of June 4, Squadron Leader Jeaff H. Greswell picked up an ASV contact and commenced the first combat approach with a Leigh Light. His target was the Italian submarine Luigi Torelli, commanded by Augusto Migliorini, outbound from Bordeaux to the West Indies. Greswell homed on Torelli by radar, then switched on the Leigh Light, but owing to a faulty setting in his altimeter, his approach was too high and he saw no sign of a submarine. However, Migliorini, mistaking the Wellington for a German aircraft, fired recognition flares, precisely pinpointing his boat. On a second approach with the Leigh Light, Greswell got Torelli squarely in the brilliant beam and straddled her with four shallow-set 300-pound Torpex depth charges from an altitude of fifty feet. The blasts savaged the boat, forcing Migliorini to abort.*
Suhren reached France safely the next day. He found the Kerneval staff in a minor uproar about the attack on Torelli. Notwithstanding repeated assurances to the contrary by technical authorities in Berlin and elsewhere, it seemed obvious that the British had managed to miniaturize radar to fit in aircraft. Dönitz demanded that the technical services immediately produce a “radar detector” or FuMB (an abbreviation of the German phrase for “Radar Observation Equipment”). Thanks to prewar R&D by the French firm Metox-Grandin, to which they had earlier gained access, the Germans were able to quickly produce a prototype receiver and a small, crude, diamond-shaped, dismountable aerial made of wire and wood that could be set up on the bridge of a U-boat while it was on the surface. Astonishingly, this primitive FuMB (known as the “Biscay Cross”) was capable of detecting meter-wavelength radar emissions at up to 18.6 miles and to warn of them by emitting a “whistling” or “humming” noise. Dönitz issued orders to equip all U-boats in the Atlantic force with a FuMB, but the order could not be carried out fully until early September.
The other fifteen VIIs of the April group sailed for the Americas day by day. Inasmuch as the weather in Canadian waters had dramatically improved and Dönitz wished to hold Allied ASW forces there to the greatest extent possible and to disrupt North Atlantic convoy sailings to and from Halifax, Sydney, and St. John’s, he directed four of the boats to patrol off Newfoundland and Nova Scotia. The other eleven were to continue south to the United States East Coast and to the Bahama Islands, east of Florida. If the planned refuelings with U-459 were successful, five of the Type VIIs were to go further yet and explore the distant Caribbean Sea and the Gulf of Mexico.
Three of the four boats assigned to patrol Canadian waters had made prior patrols to the Americas: Heinz-Otto Schultze in U-432, Karl Thurmann in U-553, and Viktor Vogel in U-588. The fourth was the Type VIID minelayer U-213, commanded by Amelung von Varendorff, who had made one prior patrol in the defense of Norway. Before attacking any shipping, von Varendorff had first to carry out an unwelcomed special mission: to land an Abwehr agent on the coast of New Brunswick.*
Two of the four Canada-bound Type VIIs, Thurmann’s U-553 and Vogel’s U-588, were diverted for several days in the futile hunt for the big troopship convoy AT 15-NA 8. Released from that duty, both approached Canadian coastal waters behind schedule. On May 6 Thurmann shot at a freighter escorted by a “corvette,” but the torpedo failed or missed and the escort drove him off with depth charges. On the following day, an aircraft dropped three close “aerial bombs,” which caused considerable damage to the boat. Seeking a “quiet” area to make repairs, Thurmann limped through Cabot Strait into the Gulf of St. Lawrence, a large, shallow, landlocked body of water at the mouth of the St. Lawrence River,† which to then had not been penetrated by U-boats.
The other VII, Viktor Vogel in U-588, took up station directly off Halifax, Nova Scotia. On May 9 he attacked and damaged the 7,500-ton American freighter Greylock. Harassed by ASW air and surface patrols, Vogel slowly inched south to Cape Sable. Near there on May 10, he sank the 4,000-ton British freighter Kitty’s Brook. His attacks temporarily froze the Boston-Halifax-Boston convoys and other fast ships sailing alone.
After completing repairs to U-553, Thurmann, on his own initiative, decided to explore the Gulf of St. Lawrence. He crawled slowly northwest toward Anticosti Island, which lies off the Gaspe Peninsula in the broad estuary of the St. Lawrence River. While U-553 was incautiously cruising the surface on the afternoon of May 10, an American B-17, based at Gander, saw and attacked her, dropping five bombs or depth charges from an altitude of about 2,300 feet. Although these explosions caused severe damage to the boat, Thurmann pressed on toward Anticosti. The American airmen were dilatory in reporting their attack to other Allied ASW forces in the area, so no follow-up air-sea hunt was mounted and the danger U-553 presented to the river traffic was not immediately appreciated.
In a remarkable and bold thrust, which was to be likened to Prien’s penetration of Scapa Flow, Thurmann reached the mouth of the St. Lawrence River by the early hours of May 12. Within the first four hours of daylight, he spotted five big, outbound, oceangoing freighters and shot torpedoes at four. He claimed sinking three ships and a hit for damage on the fourth. Postwar records credited two freighters sunk: the 5,400-ton British Nicoya and the 4,700-ton Dutch Leto.
The presence of U-553 in the Gulf of St. Lawrence caused an uproar. Dönitz, the U-boat staff, the Canadian government, and Allied ASW forces were equally thunderstruck. The Allies temporarily froze all gulf and river shipping, extinguished navigation lights, and saturated the gulf with ASW air patrols. With nine torpedoes remaining, Thurmann lay low for a week, making repairs, eluding enemy aircraft and warships, and patiently waiting for the resumption of ship traffic. Finally, on May 21, he gave up and exited the gulf via Cabot Strait. Upon receipt of Thurmann’s report, Dönitz replied with congratulations. Praising Thurmann by name, Berlin propagandists crowed over his feat, implying that U-boats were operating with impunity in the Gulf of St. Lawrence.
Meanwhile, the third VII of the group assigned to Canadian waters, von Varendorff in the Type VIID minelayer U-213, arrived to land the Abwehr agent. Logged aboard U-213 as Kriegsmarine lieutenant “M. A. Langbein,” the agent carried forged papers in the name of “Alfred Haskins” of Toronto. His probable mission was to report the sailings of Halifax convoys and other military information. He had a portable radio transmitter-receiver, civilian clothes, and $7,000 in U.S. currency. Entering the Bay of Fundy, von Varendorff landed the agent via rubber dinghy on Melvin’s Beach, near the town of St. Martins, New Brunswick, in the early hours of May 14.* Von Varendorff then explored the Bay of Fundy for enemy merchant ships, but found none.
The fourth and last of the Canada-bound boats, Schultze in U-432, reached the Nova Scotia area in mid-May. He cruised south to Cape Sable, where on May 17 Vogel in U-588 sank the 2,100-ton Norwegian freighter Skottland but missed the British freighter Fort Binger, which was manned by a Free French crew who aggressively counterattacked Vogel by gun and drove him off. East of Cape Sable that same day, Schultze in U-432 attacked and sank by gun the 325-ton Boston-based fishing trawler Foam. At about this same time, von Varendorff in the VIID minelayer U-213, having found no shipping, exited the Bay of Fundy at Cape Sable.
The U-boat staff was puzzled that none of the four boats assigned to Canadian waters had found a major convoy. Believing the Allies may have shifted the routes farther offshore, Kerneval ordered Vogel, von Varendorff, and Schultze to recon-noiter an area about 200 miles southeast of Cape Sable. Leaving the Gulf of St. Lawrence, Thurmann in U-553 replaced the three boats in the Cape Sable area and explored the Bay of Fundy.
Taking up the assigned stations well to the southeast of Cape Sable, Vogel, Schultze, and von Varendorff found no convoys but encountered numerous ships sailing alone. On May 21 and 23, Vogel in U-588 sank two by gun and torpedo: the 3,300-ton American freighter Plow City and the 4,500-ton British freighter Margot.* Having expended all his torpedoes to sink four confirmed ships for 14,000 tons, Vogel set a course for France. Nearby, Schultze in U-432 sank the lone 4,500-ton British freighter Zurichmoor, then returned to the Cape Sable area, switching places with Thurmann in U-553, who was running low on fuel and food. While 240 miles due south of Cape Sable on June 2, Thurmann in U-553 sank the 7,000-ton British freighter Mattawin. Although he was nearly out of food and had but three torpedoes and little fuel remaining, Thurmann was reluctant to head home. However, on June 11, a Catalina found and attacked U-553, dropping two close depth charges which disabled the port diesel and forced Thurmann to abort. On May 26, von Varendorff in the VIID minelayer U-213 chased a freighter for eight hours to achieve a favorable firing position, but all three torpedoes missed.
Three of the four April boats that were assigned to Canadian waters did not refuel. Von Varendorff in the VIID minelayer U-213, which had 50 percent greater fuel capacity than a VIIC (169 tons vs. 113 tons), had no need to replenish. Upon completing his patrol of sixty days, during which he successfully landed the Abwehr agent but sank no ships whatsoever and came home rather soon, von Varendorff drew a stern rebuke. Thurmann in U-553 and Vogel in U-588 carried out patrols of sixty-seven and fifty days, respectively.
Returning to the Cape Sable area, Heinz-Otto Schultze in U-432 had a busy time. On May 31 he sank a 1,200-ton Canadian coaster. On June 2 he sank by gun two small American fishing trawlers: the 41-ton Aeolus and the 102-ton Ben and Josephine. Citing these sinkings and that of the trawler Foam, some historians were to condemn Schultze for ruthlessness. But apparently Dönitz and/or the U-boat staff encouraged such attacks in the belief that fishing trawlers and other small craft reported U-boat sightings by radio.*
While about seventy miles southwest of Cape Sable on June 9, Schultze in U-432 found a convoy. He reported twelve freighters escorted by “two destroyers, two corvettes, and a blimp.” Since no other boats were nearby, Kerneval authorized Schultze to attack alone. Firing a full bow salvo at two big freighters, he claimed sinking one 8,000-tonner and damaging another, but the records confirmed only damage to the 7,000-ton Norwegian vessel Kronprinsen. Low on fuel and torpedoes, Schultze set a course for France, refueling from U-459 on the way. Since his claims and credits for this and prior patrols exceeded 100,000 tons, he was awarded a Ritterkreuz.†