Whether out in the North Atlantic, up in the Arctic or throughout the Mediterranean, the cutting edge of German naval power – the U-boat – was being blunted by an increasingly effective Allied response that used intelligence gained through Enigma decrypts, stronger escort groups and more plentiful aircraft equipped with the latest technology to shield more of their convoys from them while on passage. Worse still for Dönitz, improved convoy protection came with an increasing ability to locate and destroy his U-boats whether they operated in groups or as individual entities. In the place where they had formerly thrived the most – the North Atlantic – the monthly returns were very revealing. From 22 February to 22 March, thirty-six U-boats spread-eagled across the ocean had been able to sink two destroyer escorts, a corvette, a landing ship, and a tanker and shoot down three aircraft, but had suffered ten losses and one damaged U-boat in doing so. If it was a sign of the times it was a depressing one for the U-boat arm and its greatest supporter. Unfortunately for both, the results over the next six weeks were even more dismal. Despite the presence of seventeen U-boats between Newfoundland and the Irish coast only two ships and two more enemy aircraft were dispatched, while eight more U-boats were sunk and another one was damaged. Even if they could be sustained in the short term, losses of this kind made little sense. Dönitz had seen enough; for the time being at least the war against trade had to be considered as being lost on the high seas. He could return to it once his new generation of U-boats had made it off the test beds or when he had more schnorchel boats available to him. Meanwhile, he considered that his U-boats might be more profitably used in the coastal waters off the British Isles where there was increasing activity as preparations intensified for a major amphibious operation in the months to come.
Although he saw little choice in pulling back his U-boats from the Atlantic, Dönitz still hoped that they could recapture their past glories in northern Europe. It was a vain hope. In their exploits against four convoys (JW. 57/ RA. 57, JW. 58/RA. 58) stretching from late February to early April, thirty-one of his U-boats were used in six different groups. Despite locating the various convoys and carrying out many attacks on them, they rarely succeeded in penetrating the escort and support group screens surrounding the 158 ships on offer – a fact exemplified by the sinking of only a solitary freighter and a destroyer escort in addition to the shooting down of a patrolling aircraft in many days of sustained activity. In compiling this modest record, nine U-boats were sunk, another one was badly damaged and six accompanying aircraft were destroyed. Dönitz could be forgiven for wondering how long this nightmare might last.
Something was clearly amiss. Acoustic as well as pattern running torpedoes were not striking home with the regularity that they were designed to achieve. Near-misses were not good enough. Were they the product of design flaws, poor marksmanship by his U-boat commanders, or aggressive hunting methods adopted by the enemy? As with most things, the blame for these lamentable failures could be apportioned all round. Nonetheless, one development was becoming very noticeable, namely, that if contact was made with a U-boat, the escort and support groups locating it would continue their pursuit for hours on end and their pattern of depth-charging and the weapons of destruction at their disposal, such as the `Hedgehog’ and the new `Squid’ mortar, would more often than not finally win the day. For this reason, Dönitz realised that his boats must remain submerged for as long as possible so as to avoid detection. This, of course, was the singular advantage which the new schnorchel boats offered. While evading detection was a crucial asset for any submarine, the breathing tube which these new vessels could float to the surface at night time to replenish air supplies was ruled out during daylight hours because it could be spotted by alert and trained observers. Therefore, to preserve oxygen during the day while they remained submerged, the crews of the schnorchel boats were forced into spending many silent hours on their bunks. At night, however, the same privations could be eased with U-boat commanders employing the schnorchel breathing tube while remaining submerged and using their diesel engines to make headway although, admittedly, at a slower pace than if they were travelling on the surface.
Dönitz’s marked lack of achievement in the Arctic was more than matched by the laboriously sterile operations of the Soviet Northern Fleet in attacking German convoy traffic around the Polar Coast. Allied efforts to strike a more emphatic note in these waters were illustrated by their repeated attempts to finish off the damaged battleship Tirpitz which remained in Altenfjorden after the earlier midget-submarine operation of September 1943 had damaged but not sunk her. A sense of frustration grew as the year went on and she remained in existence. Fifteen Soviet bombers tried to destroy her with 1,000 pound (453.6 kilo) bombs on 11-12 February, but only one near-miss resulted from that foray. Although she didn’t represent an imminent danger to Allied shipping in her existing condition, once she had been fully repaired, she would present the same old dangers that the Scharnhorst and the Bismarck had posed before her. `Ultra’ intelligence gleaned through the work of the Bletchley Park cryptanalysts left the Admiralty in no doubt that she had been patched up sufficiently by early April to make her anticipated return journey to a naval base in Germany for a thorough overhaul. An attack was judged vital and Vice-Admiral Sir Henry Moore was asked to launch Operation Tungsten at dawn on 3 April spearheaded by fighter aircraft from four escort carriers to deal with enemy planes and strafe the deck and bodywork of the Tirpitz if she could be found and pave the way for the forty-one Fairey Barracuda bombers from the fleet carriers Furious and Victorious to finish her off with an arsenal of armour-piercing, semi-armour-piercing and high-explosive bombs. Despite a partial smokescreen, Tirpitz was found by the Corsairs and Hellcats, and strafed accordingly and then the Barracudas managed at least fourteen hits or near-misses, in two waves of attacks. Although the damage caused was very significant – Eric Grove describes the upper decks as being `reduced to a shambles’ – the bombs did not penetrate below the armoured deck. Notwithstanding this failing, the damage done was such as to ensure that the battleship was not going anywhere fast and the trip to Germany was put off once more until the new damage could be repaired.
Despite struggling to eliminate the last of the German capital ships in Norwegian waters, the Allies still enjoyed considerable success in this theatre of operations. Apart from the Arctic convoys that largely defied all that the Luftwaffe and Dönitz’s U-boats could throw at them, and the exploits of their own submarine crews in these waters, it was the aircraft of 18 Group Coastal Command that really made a dramatic impact off Norway by waging war on both those conventional and schnorchel-fitted U-boats that were endeavouring to use these waters to gain access to the Atlantic. In a series of attacks they launched over a five-month period from late February to late July, they destroyed seventeen U-boats, damaged fifteen others and forced several others to either return to port or interrupt their transit journeys. Disturbing though these figures were for the officers of the Kriegsmarine, the more worrying aspect was that the schnorchel boats were being identified and picked off in daylight by vigilant air crew that looked for tell-tale signs of a foaming wake left behind by these vessels. Although the U-boats had exacted some revenge by downing five of the Allied aircraft and badly damaging six others, the cost-benefit analysis was distinctly going against the Axis forces in these northern latitudes as it was elsewhere.