Indicadores de Desempeño de una IMF

Bismarck was sunk, but her supply ships were still at large in the Atlantic, and no time was lost

in using them to refuel the "West Group." One U-boat after another came up to lie astern of the tankers, drawing in the oil through their long fuel lines. Claus Korth in U 93 was one of the many captains who refueled in this way, but as he was in the middle of doing so, the tanker signaled: "Enemy destroyer in sight" and almost at the same moment the air was filled with bursting shells. In a trice Korth had disconnected the fuel lines and had begun to dive; through his periscope he could see the destroyer's shells crashing into the tanker's sides, as her crew took to the boats. The one-sided action was soon over; Korth had no chance to counterattack, for the enemy kept carefully out of his range and disappeared as soon as the tanker had sunk.

Korth surfaced and took on board the fifty survivors who, added to his own crew of forty-three, crowded together in every compartment of the U-boat. There was barely room to stand up, let alone lie down. As Korth began his return journey he ran into a convoy, but he reluctantly decided that his boat was too crowded to go to action stations, and he let the convoy go. Back in Kernevel, however, the admiral rebuked him severely. "What on earth have survivors got to do with it? You were sent out there to fight! Our biggest headache is to find the enemy. You find him and then you let him get away, just because you have survivors on board. You could at least have shadowed for the other boats. . . ."

"Never mind, Claus," said the flag lieutenant, as the chastened officer emerged from the admiral's office. "It's not as bad as all that. Come in here." He led the way into the operations room. "We're really up against it. Look at this— it's a new system of charting the dispositions of

all the enemy's warships and merchant ships." He pointed to a number of regional charts. "Information from every source is entered here," he said, "U-boat signals, air-reconnaissance reports, messages from the intercept service and from agents, weather reports from trawlers— everything of interest sighted and reported by German or Italian U-boats or decrypted from enemy messages. It also shows what we think the enemy is likely to have picked up from our boats' sighting reports, or from his own aircraft sighting reports, or from his secret agents. All this is necessary because otherwise we can't find the enemy. You yourselves can't find him— except by chance; and we cannot run a successful campaign on mere chance."

The Bismarck action had shown that the enemy had a radar-location device similar to that of the Germans; and although in June and again in July, German aircraft had reported convoys giving cross bearings for the U-boats to follow, the convoy in each case had taken evasive action before the boats could reach it. It was still uncertain whether this was due to chance, or whether the enemy had managed to escape by using radar or by taking D/F bearings on German radio transmissions.

The German Admiralty now required another ten or twelve boats up north for attacks on the Allied convoys to Russia, but Dönitz protested that he could not spare even one boat from the Atlantic; he maintained that every ton of cargo or shipping destroyed in the Atlantic was potentially a ton lost to Russia. "Our job is to sink ships quicker than the enemy can replace them," he reiterated, "and to do so where it is easiest for us. To split up our forces now will reduce the sinkings. Today each boat is achieving less than in the autumn of 1940."

Another worry was the drop in U-boat construction. A shortage of copper was given as the reason for the production rate falling from twenty-five to fifteen boats every month, but Dönitz would not accept this excuse so long as any copper roofing or bronze statues of doubtful artistic value remained in Europe. The time taken for repairs was also unsatisfactory; out of every 100 days, a U-boat was spending 65 in the dockyards and only 35 at sea. The proportions should have been 40 and 60 days, or even 50-50, but at this time no fewer than 800 dockyard workers were actually being withdrawn from work on U-boats to reconstruct the Hipper's fuel tanks. By an error, one of Dönitz's many minutes on this subject was returned to him, with a revealing marginal comment: "We don't want to become a Navy of U-boats." That summed up the Admiralty's attitude.

Some commanders now reported that even the enemy merchant ships were carrying detecting gear. One of these commanders was Endrass (U 46), who had been Prien's first lieutenant at Scapa Flow, and had since proved himself an outstanding captain. Having sighted a fine large tanker, he approached her as night began to fall. He was quite confident that he had not been observed, but even as he closed the tanker she began to move in short, sharp zigzags; just as he fired his torpedoes she turned straight toward him; it was evident that she was fitted with asdic. The two adversaries circled round each other until dawn, but then one of Endrass's diesel

couplings began to give trouble and he had to abandon the chase while his engineers wrestled for fourteen hours to put the damage right.

The U-boat captains were also worried about the poor performance of their torpedoes. Lieutenant "Recke" Lehmann-Willenbrock was one of many who complained on this score. One ship, he said, required four torpedoes and also some rounds from the gun before she would sink. What was needed was an effective noncontact pistol which would explode the torpedo immediately under the target and thus cause far greater damage than a contact torpedo.

When the search for targets in the extreme western waters proved fruitless, the U-boats were brought back to more easterly areas, since it was preferable to make sure of locating the convoys

even under more difficult conditions of attack, than to miss them altogether in undefended

waters. Moreover there were improved prospects of cooperation with the Luftwaffe. On taking up his post as A.O.C. Atlantic, Lieutenant Colonel Harlinghausen, as an experienced sailor, had immediately understood what the U-boats required. The convoys sailing between Britain and Sierra Leone were going so far out to the west that the German aircraft could only shadow them for a few minutes before shortage of fuel forced them to turn back. All they had time to do was to send out beacon signals; even if they were able to make a proper sighting report, their

navigational fixes frequently lacked accuracy, while their beacon-signal transmissions often did not last long enough for the U-boats to get a proper fix. Harlinghausen now proposed a new system whereby, upon sighting a convoy at the extreme limit of his plane's endurance, the pilot transmitted beacon signals to the A.O.C., who warned the U-boat Command to notify the U- boats. All this required only a few minutes. The aircraft then continued to emit beacon signals which the U-boats could pick up and, before leaving the convoy, the pilot would also signal his position.

This system soon proved its worth. With the help of the aircraft the U-boats were able to maintain contact with a convoy for as long as eight days in succession. The sinking figures rose still higher.

[For Great Britain the summer of 1941 was perhaps the most anxious period of the whole war, for the volume of imports reaching the United Kingdom was steadily diminishing.]

Another source of worry at this time was that the U-boat captains' reports of sinkings were proving less reliable than in the early days. The efficiency of the A/S escorts compelled the captains to deliver their attacks swiftly and then clear out, which provided no opportunity to check the running time of their torpedoes with stop watches or to establish the size of a sinking ship through the periscope. The men on the admiral's staff who kept the secret records began to discover, for example, that the tonnage of the Gibraltar convoys, which consisted mainly of smaller ships, was often overestimated by the attacking U-boats.

One group of boats had been patrolling for three weeks to the northwest of Ireland without finding a single ship; on the other hand, reports were coming in from all quarters of strong enemy air activity. How was it that the British were suddenly able to reinforce their air patrols in the Atlantic? What conclusions should be drawn from the fact that U-boats approaching a

convoy at night were very quickly attacked by destroyers deliberately detached for this purpose? The boats trying to attack the Gibraltar convoys, for example, found that the air and surface escorts had been considerably strengthened. The enemy had made much progress in the technique of denying approach to the U-boats; by day the outer screen prevented them from getting near enough to the close screen to identify the layout of the convoy as a whole, and by night the outer screen moved inward to reinforce the close screen, so forming an impenetrable cordon round the ships.

It was evident that the principal menace lay in the enemy's use of radar, and Commander Meckel, the Staff Communications Officer at U-boat headquarters, was called in to suggest possible antidotes. Meckel's first proposal was to find some way of covering the boats' hulls with a material that would absorb the radar impulses. He went on to say that a search receiver would have to be found that would register the enemy's radar transmissions; there might be some possibility of installing a search radar in the boats such as was used in destroyers and big ships, but he thought that this would have a very limited range in U-boats because of lack of height in the aerial. On being asked if it was possible that enemy aircraft were also using radar to locate surfaced boats, Meckel thought it highly improbable, as the necessary equipment would be too

heavy for an aircraft to carry. He then requested and received permission to discuss these problems with the Admiralty experts in Berlin.