The intelligence derived from breaking Enigma transmissions — the product was known as Ultra in Britain, because it had the highest of all security classifications — was of vital importance in fighting the Battle of the Atlantic. The identification of U-boat movements through Ultra intercepts allowed convoys to be directed away from their patrol lines, aircraft to be vectored to their positions and escort groups of destroyers and frigates to be hurried to their concentration areas. The cipher war in the Battle of the Atlantic swayed one way and another. British naval codes, particularly the Long Naval Code No. 3, were read by the Germans while the British were reading Enigma. At the end of 1942 and well into 1943, the British lost the U-boat key altogether, with calamitous results for convoy sailings. Overall, however, Ultra intelligence was a crucial factor in the winning of the Battle of the Atlantic against the U-boats.
This description of the effects of escort attack on a U-boat during a convoy battle graphically conveys the horror of a successful depth-charging. By November 1943, to which this episode dates, the Battle of the Atlantic was largely won. A determined U-boat could still inflict damage unless relentlessly attacked and kept down, as U-333 was by HMS Exe, a River-class sloop, one of the hundreds of small ships that were the mainstay of the Allied effort in the Atlantic battle. Kapitan-leutnant Cremer survived this, his second, patrol, against Convoy SL (Sierra Leone) 139, but was sunk on his fifth, in July 1944. A majority of U-boats were sunk on their first patrols. The U-boat force lost 70 per cent of its manpower during the war, the highest proportion of casualties suffered by any arm of service in any combatant country.
On 13 November the sailing was reported of a convoy with ships from Gibraltar and North African ports which next day joined up with a Sierra Leone convoy about 100 miles south of Cape St Vincent and now consisted of 66 freighters: it was code named SL 139/ MKS 30. To start with it was accompanied by 40th Escort Group, but during the passage to Britain 7th and 5th Escort Groups were fetched from other convoys and the 4th from Belfast, so that the 66 merchant ships were gradually surrounded by 28 escort vessels: frigates, corvettes, destroyers and the Canadian anti-aircraft cruiser HMCSPrince Robertwhich had come from Plymouth — the Luftwaffe now had only a fitful presence over the ocean, but reconnaissance aircraft and even bomber formations were occasionally spotted. RAF Wellingtons from 171 Squadron in Gibraltar provided air protection, reinforced by Mosquitos and Beaufighters off Cape Ortegal. Direct convoy protection was then to be assumed by aircraft from Cornwall (RCAF [Royal Canadian Air Force] 422 Squadron and RAF Liberators from 453 Squadron).
Against this doubly and trebly screened convoy we had the Schill Groups I, II and III in three stop lines about a day’s sailing apart. Air Command Atlantic was involved with 25 long-distance bombers of type HE [Heinkel] 177. This time the convoy battle promised to be both vast and varied.
On 16 November the convoy was first sighted by a German aircraft, and thereafter there were several sightings. In the morning hours of 18 November the ships sailing up from the south came into action against the U-boats on watch in the north. The scene was roughly midway between the Azores and the Portuguese coast. This was a grey November morning after a clear moonlit night. The sickle stayed for a long time in the sky before it was properly light. Small clouds came up. A slight wind was blowing from the north-east, and when the sun shone in the course of the morning it showed a sea stirred into a slight swell by the winds of recent days. U-333 was moving underwater and when I occasionally raised the periscope spray splashed against the lens. The empty horizon was a sharp dividing line which in the rhythm of the sea rose up, then disappeared behind the wave-tops. The clock showed 11.30.
It was relatively quiet in the boat. Amid the gurgle and wash of the water came other sounds, weak at first, then growing stronger. The operators signalled ships’ propellers from the south. I let things start gently and hung on the periscope. After a while the silhouette of a great many freighters appeared. Fourteen rows of ships were coming in their full width with foaming bow waves directly towards me. It was a unique sight: the expected convoy SL 139/MKS 30. Chance would have it that U-333 was the first boat to intercept the enemy.
In front sailed two escort vessels, clearly destroyers. U-333 lay roughly in the middle between them, in an attack position which would probably not recur. I only needed to let myself drop into the convoy and attack like a pike in a carp pond. All tubes were ready for an underwater shot, flooded and with bow caps open. All I had to do was lie still, let the enemy draw closer and then: at him with a roar! But everything turned out quite differently.
The destroyers were signalling to one another. The right-hand one was zig-zagging continually while the left kept to a straight course. I had my periscope up again, hoping it would not be noticeable in the light motion of the sea, when suddenly I saw an aircraft flit past my lens barely 30 metres above the water. At the same moment the locating signals of the enemy Asdic [sonar — underwater sound-ranging system] struck the U-boat’s side with their horrible ping-ping-ping-ping, so loud I might have sent them out myself. We had been discovered. Involuntarily everyone held his breath.
The left escort, it turned out to be the frigate Exe, was already turning towards us and in a moment was so close I could distinguish details on deck. I intended to fire a spreading salvo of three into the convoy and had already ordered ‘salvo ready’, meaning after previous misses to be on the safe side and let the ships come closer, despite the menacing frigate whose sailors I could now see running to and fro. I was still staring obstinately through the periscope when a pattern of ten depth charges exploded with a deafening roar round the boat. We had got into the middle of a carpet.
The effect was terrible and is hard to describe. Suddenly everything went black and everything stopped, even the motors. In the whirl of the shock waves the rudderless boat was seized like a cork and thrust upwards. There was a cracking and creaking noise, the world seemed to have come to an end, then crashes and thuds as the boat was thrown on to its side and everything loose came adrift. I managed to grab the steel strop on the periscope, then my legs were pulled from under me. We had collided with the frigate’s bottom which was now thrusting away above us, steel against steel. Certainly the British were no less shaken than we, seeing that [according to a British after-action report] ‘just before the first charge exploded, the ratings on watch in the boiler room heard the periscope scrape down the side’ ...
Seconds later, the periscope broke off. The swaying boat reared up, struck the hull of the Exe with its conning tower and the control room and listening compartment immediately flooded. The water quickly rose above the floor plates. The light of a torch lying on the chart table showed a picture of devastation. All the indicator gear was hanging loose, the glass was splintered, light bulbs had burst. Cable ends spread in bundles through the control room, the emergency lighting accumulators [batteries] had torn free. Before I even got to the depth-keeping controls the boat was again shaken by the heaviest depth charges. Like a stone we slipped backwards towards the ocean bed which here lay 5,000 metres below.
From the engine room the hydrostatic external pressure, indicating depth, was passed on from mouth to mouth and the fall of the boat stopped by blowing the tanks with compressed air. It rose slowly, then faster and faster until it had to be flooded again so as not to shoot out of the water like an arrow. Beams from the torches flicked over the walls glistening with moisture. It trickled and poured. As none of the pumps was working the water that had come in was transferred in buckets from hand to hand from the lower-lying stern — where it was already above the coaming of the alleyway hatch — into the central bilge. Gradually the boat swung back from the slanting position to the horizontal.
Fortunately the switchboard was still dry, there was no short circuit. We could put back the knife switches which had fallen out and in feverish haste got the electric motors working. Though the noise of the port propeller shaft showed that damage had been caused, its turning again was music in our ears.
My log says: ‘Decide to hold the boat by all possible means and slowly go deeper. Damage very great and cannot yet be assessed.’
From the British viewpoint we were ‘in the centre of the (first) pattern when it exploded’ and ‘the first attack must certainly have damaged the U-boat so severely that it was unable to surface.’ When an oil patch was sighted at 11.56 and a sample was collected it was believed we had sunk.
But in fact we had let ourselves drop from 60 to 140 metres. Meanwhile the entire convoy in its whole length went thumping past us overhead. In such a situation that is about the safest place for a stricken U-boat, particularly as any hydrophone [acoustic] contact is lost in propeller wash. Nothing can touch one, unless perhaps a ship is torpedoed and falls on one’s head.
But hardly was the mass of the ships past than we were overwhelmed with a drumfire such as I had never yet experienced. And that is saying a lot. It began at midday and went on till 20.55 like a continuous thunderstorm, now close, now further away, the heavy-sounding depth charges and the lighter Hedgehogs [multi-barrelled mortar bombs]. And each time we thought, ‘Now there’ll be a direct hit,’ but in fact the explosions detonated further away, we had to wipe the cold sweat from our faces. So-called heroism has not much to do with it. And when finally the torture ended and the great silence began we refused to believe it, but stood there wide-eyed, gasping and struggling for breath, waiting for the next series.
Luckily we had little time for reflection. There was too much to do. The worst damage had to be repaired. Damage to instruments (speed and trim indicators, water and pressure gauges, depth recorder) belonged to the lesser evils. Broken telephones and radio could be accepted. Even a destroyed fire-control panel lost significance for survival, particularly as the heads of all the torpedoes in the tubes had been dented, not to mention the plastic cap of my acoustic torpedo which I had thought so important ...
But the starboard diesel had been thrust sideways and fallen from its base, and this was more than problematical. Now by the sweat of our brow we had to wedge and support it with beams. And hardly less serious was the port propeller shaft, which had been bent and was hammering loudly. To complete our misfortune, the radio installation was so badly damaged that despite trying three times I was only able to send a short mutilated signal.
Air was running out. Our bodily exertions had used it up quicker than usual and it had to be improved with potash cartridges and oxygen. There was a stink of battery gas — the ventilation lines had been broken - and of watery oil. Eventually the fug became chokingly thick, and compressed air was getting short. After nine hours of depth charging which had thoroughly shaken the boat and had necessitated our repeatedly blowing the tanks to maintain station, there was hardly any compressed air left. The boat was tending to lose depth again and could be kept trimmed only with difficulty. I had to go up regardless, and so, one hour after the last charge had exploded and the great, perhaps deceptive silence had fallen, I brought U-333 to the surface.
Up above it was dark. Sea state 5 to 6 with heavy swell, the slim outline of the boat hiding in the troughs. Somewhere there was a destroyer, but she spotted nothing. The watch came up and we inspected the scope of the exterior damage. The forward net-cutter was broken, the bridge cowling bent forward. Both periscopes were useless, the attack periscope bent, the night-sighting periscope broken. Radio direction-finder and anti-aircraft guns had gone, as though shaven off. The lurching boat had a list. It was only just floating above water, and I had another shock, in so far as one was capable of more, to see air bubbles surging from both sides. Apparently all the ballast tanks had cracks. U-333 could float only to a limited extent.
The diesels would not start. Despite repeated blowing, the boat would not stay on the surface but slowly sank downwards by the stern. We had to submerge again so as not to drown on the bridge. Last man down as always, I shut the conning tower hatch — or tried to. This time it stuck. Meanwhile the boat was submerging completely and streams of water poured through the opening. I clung to the wheel until I fell into the control room. We blew the last of the compressed air into the tanks and the hatch slowly emerged from the swirling water. I had swallowed a great deal, was soaking wet and numbed, but with the help of the 2WO , was clearheaded enough to find the curious cause of the defect: part of a blade knocked off from the propeller of the frigate Exe had slipped and blocked the hatch.
Things were against us — as though a renewed attempt was being made to do away with us. After many experiments we finally got the port diesel going — it began to function ‘slow ahead’ — and eventually the starboard diesel started as well. The ballast tanks were no longer airtight, but with the exhaust gases we blew into them we could roughly keep a balance with the water coming in. But the boat was still more or less unstable and threatened to drop away under our feet. And somewhere water was continually dribbling inboard where we struggled with the damaged pumps. We had no alternative but to move ‘dynamically’ and gently get away.
Next day already on the way home I wrote in the log: ‘Surfacing goes better’, and the day after, ‘considerably better, which means I have got accustomed to the condition of slowly sinking.’ Though that speaks volumes, it says nothing about our wet feet. Yes indeed, we had been given a pasting. My people patched everything possible with what lay to hand. That was very little. And so we went hobbling home with a wreck. And with all the iron around us, navigated with the magnetic needle alone, for the gyro compass too was broken.