The arrival in France of four new Type IXs and exceptionally efficient refit operations at the French bases enabled Dönitz to order twenty-one boats to American waters in May: twelve Type VIIs and nine Type IXs. Notwithstanding increasing risks and declining returns, all the Type VIIs and one older, short-range IXB, U-124, were directed to patrol the United States East Coast waters. The eight other longer-range IXs were to be evenly divided between the Gulf of Mexico and the Caribbean. The May boats were to be supported by the tanker U-459 and by the big XB minelayer, U-116, which resailed May 16 after twelve days in port for battle-damage repairs.
By this time codebreakers at B-dienst had developed what the OKM diarist characterized as “excellent” information on the routes and sailing dates of North Atlantic convoys. Noting that the Type IXB U-124 and six Type VIIs were to sail for the Americas at about the same time in early May,* Dönitz ordered them to form a group and rake the North Atlantic convoy routes as they proceeded westward. If they found and attacked a convoy, several purposes could be served. The battle would toughen green U-boat crews, ferret out new Allied detection gear and weaponry, and—hopefully—discourage further transfer of ASW forces from the North Atlantic run to the Caribbean. Should a battle develop, the big XB minelayer U-116 was to sail in exclusive support of the group. After replenishment from U-116, the boats were to proceed to American waters.
Designated group Hecht, the seven boats sailed from French bases May 3 to May 7. Two were commanded by young Ritterkreuz holders: Otto Ites in the Type VII U-94, and Johann Mohr in the Type IXB U-124. Of the other five boats, three were experienced and two were green. Already at sea, vainly seeking her blockade runner, the famous U-96, commanded by a new skipper, Hans-Jürgen Hellriegel, age twenty-four, onetime first watch officer to Engelbert Endrass, joined group Hecht west of the Bay of Biscay, making a total of eight U-boats.
Some of the Hecht boats were fitted with a new defensive device designed to confuse enemy sonar. Known as Bolde (probably derived from kobold, German for goblin or deceiving spirit), it was a perforated or degradable canister filled with calcium hydride that was fired from an internal tube called a Pillenwerfer (pill thrower) and floated at a depth of about 100 feet. When saltwater mixed with the calcium hydride, it generated a great mass of hydrogen bubbles for about six minutes. The bubbles reflected sonar pulses, giving off an echo that, to an inexperienced sonar operator, sounded like a submarine hull. The hope was that by laying a trail of Boldes between it and a pursuing enemy, a U-boat might elude sonar.*
Acting on the “excellent” intelligence on Allied convoys generated by B-dienst, group Hecht raked westward along specific sea-lanes. In the early hours of May 11, one of the experienced boats, U-569, commanded by Hans Peter Hinsch, made contact with a convoy, Outbound North (Slow) 92, in mid-Atlantic. It was escorted by the American escort group A-3. The group was composed of the big Treasury-class Coast Guard cutter Spencer, the modern (1940) American destroyer Gleaves, and four Canadian corvettes, one of which, Bittersweet, was equipped with Type 271 centimetric-wavelength radar. A rescue ship, Bury, trailing the convoy, was fitted with Huff Duff.
Hinsch in U-569 got off a contact report which brought up the two Ritterkreuz holders, Ites in U-94, and Mohr in U-124. The rescue ship Bury DFed Hinsch’s transmissions, but the American escort commander, John B. Heffernan (in Gleaves), failed to appreciate the full extent of the impending danger. That night Mohr easily penetrated the thin, unalert screen. In two separate, close attacks, he fired seven torpedoes at overlapping columns of ships. He claimed sinking five vessels for 19,000 tons and damage to one; postwar records credited him with sinking four freighters (three British, one Greek) for 21,800 tons. Coming in behind Mohr, Otto Ites sank one confirmed freighter for 5,600 tons, from which he captured the captain. The shadower, Hinsch in U-569, claimed one ship sunk but it could not be confirmed.
During the next day, May 12, six of the eight boats of group Hecht made contact with the convoy. The three new arrivals were commanded by green skippers on first patrols: Hellriegel in the veteran U-96, Horst Dieterichs, age thirty, in the new U-406, and Heinrich Müller-Edzards, age thirty-two, in the new U-590. Only one of the six boats had any luck. Ritterkreuz holder Otto Ites sank two more freighters for 8,900 tons. He approached the lifeboats of one sinking ship, the Swedish Tolken, to capture her captain, but gunners still on board the ship drove U-94 off and under. Foul weather and poor visibility thwarted further attacks. Assessing the damage—seven confirmed ships sunk—the staff at Western Approaches severely criticized the performance of the American and Canadian escorts. The Canadian naval historian Marc Milner wrote in his book North Atlantic Run that as a result, the American escort commander, Heffernan, “was quietly moved to another command.”
The easy success of Hecht against this unalert convoy and the miserable hunting off the United States East Coast in May persuaded Dönitz to change the plan. The XB minelayer U-116 replenished the eight boats of Hecht with fuel, food, and torpedoes, but only two of the seven Type VIIs were authorized to proceed to America: Otto von Bülow’s U-404 and Ernst-August Rehwinkel’s U-578. The other six boats of Hecht, commanded by three veteran and three green skippers, were to remain in the North Atlantic to exploit the information on Allied convoys coming from B-dienst.
The information from B-dienst was plentiful, but bad weather bedeviled Hecht. Nearly a month passed before the boats locked firmly onto another convoy. This was Outbound North (Slow) 100, escorted by the well-trained and experienced Canadian group C-1, which, however, had sailed minus one destroyer and one corvette (both in refit), leaving only five ships: the veteran Canadian destroyer Assiniboine and four corvettes, two British and two Free French. All five escorts were equipped with radar (four with Type 271) and the convoy rescue ship, Gothland, was fitted with Huff Duff. Additional protection was provided by the fighter-catapult ship, Empire Ocean, carrying a Hurricane fighter.
Mohr in U-124 found and reported this convoy on June 8. After Hinsch in U-569 made contact and took over as shadower, Mohr closed to attack, but the feisty, battlewise, radar-equipped corvettes blocked his approach. Undeterred, Mohr coolly shifted his attack to the escorts, firing two stern tubes at one “destroyer” and two bow tubes at another “destroyer.” The stern torpedoes missed, but the bow torpedoes hit the British-built, Free French-manned corvette Mimose, which disintegrated in a ball of flames. The other four escorts counterattacked U-124 and drove her off, thwarting Mohr’s attack on the convoy itself. At first light the next day, Assiniboine found four survivors of Mimose, but no more.
By the afternoon of June 9, all six boats of group Hecht were in contact with the convoy, but new problems arose. The three new skippers (Hellriegel, Dieterichs, Müller-Edzards) reported defective engines, probably the result of the hard chase in heavy seas. Dönitz therefore ordered those three boats to withdraw, leaving only Ites in U-94, Mohr in U-124, and Hinsch in U-569 to mount the second attack. Leading the assault that night, Ites sank two British freighters for 11,600 tons and Mohr sank one 4,100-ton British freighter. Later, Hinsch hit and stopped a straggler, the 4,500-ton British freighter, Pontypridd. Then he and Ites put her under with finishing shots, to share credit. Impenetrable fog saved the convoy from further attacks.
Numerous eastbound convoys eluded group Hecht in June. These included troopship convoy AT 16 from New York, combined with NA 10 from Halifax. This formation consisted in total of six troopships escorted by Task Force 35: the battleship New York and nine American destroyers. Three of the destroyers in this formation (Eberle, Ericsson, Roe) peeled off in Halifax on June 16 and escorted the four troopships of convoy NA 11 from there.
Following the battle with Outbound North (Slow) 100, the six boats of Hecht reversed course and combed convoy routes on the return to France, handicapped by Ites in U-94, who also developed engine problems. Ironically, on June 16, Ites found a big convoy, Outbound North (Slow) 102. Composed of sixty-three merchant ships, it was escorted by the American group A 3, which had a new commander, Paul R. Heineman. In view of the known presence of Hecht, A-3 had been beefed up to nine veteran, very alert ships: three big Treasury-class Coast Guard cutters, Campbell, Duane, and Ingham, the four-stack destroyer Leary, the Canadian destroyer Restigouche, and four Canadian corvettes. Most of the ships had radar; Restigouche had Huff Duff.
All six U-boats attempted to mount a loosely coordinated attack on convoy Outbound North (Slow) 102, but it failed. Restigouche DFed the assembly and subsequent chatter and alerted the escorts. The green skipper, Horst Dieterichs in U-406, fired a full salvo of five torpedoes at two “destroyers,” but all missed and the “destroyers” ran him off. Other escorts blocked the approaches of Mohr in U-124. Still others caught and depth-charged Ites in U-94 and Müller-Edzards in U-590 for seven and nine hours, respectively. Lucky to have survived these merciless poundings, both boats limped to France with heavy damage, where they remained for forty-one and forty-seven days, respectively, under repair and training.
Mohr reported that the convoy had escaped in fog and that further pursuit was “hopeless.” However, by chance, at dawn on June 18 he happened upon it again and unhesitatingly and audaciously mounted a lone surface attack in broad daylight, firing four bow torpedoes at three big freighters from long range. He claimed two sinkings and damage to the third ship, but postwar records credited only the sinking of the 5,600-ton American freighter Seattle Spirit. Ringing up on full speed, Mohr eluded the escorts and set a course for Lorient.
The six boats of group Hecht returned to France in the last week of June, during the height of Kerneval’s intense investigation into the possibility that the Allies had miniaturized radar for aircraft and surface-ship use. Calling up Mohr on a new radio-telephone which scrambled his end of the conversations, Dönitz asked if Mohr had detected any sign that the Allies had shipboard radar. Mohr reported that he had been forced to take evasive action seven times during his patrol but had been directly run down and attacked by the escorts only once. He therefore concluded that the Allies had not yet installed radar on the escorts(!).
Including the U-96, which had sailed earlier, the six Hecht boats patrolled for an average of fifty-seven days. They attacked three Outbound North (Slow) convoys, 92, 100, and 102, sinking thirteen ships (including the corvette Mimose) for about 62,500 tons. The Ritterkreuz holders, Otto Ites in U-94 and Johann Mohr in U-124, accounted for 92 percent of the sinkings. Mohr got seven ships for 32,500 tons; Ites got five ships for 25,500 tons. In addition, Ites and Hinsch in U-569 shared credit for one 4,500-ton freighter. The three new skippers, Hellriegel, Dieterichs, and Müller-Edzards, sank no ships.
Although the young Ritterkreuz holders Ites and Mohr had done well as usual, group Hecht as a whole had to be deemed a keen disappointment. The return on investment, including twenty-five days of exclusive support from U-116, was poor. Moreover, the numerous convoy chases were hard on the boats; refits and battle damage repairs averaged forty-three days.* On analysis, it was seen that sinkings by the Hecht boats diminished dramatically when they confronted large, skilled escort groups, as they did in the last convoy, Outbound North (Slow) 102. As in earlier times, foul weather and the fog on the Grand Banks of Newfoundland had spoiled much of the hunting.