On 24th April 1943 U-230 had departed from Brest for the the mid Atlantic to join the U-boat Wolfpacks that Doenitz was directing towards Allied convoys. As they moved up to their assigned grid square in the first days of May they were to receive a stream of messages from other U-boats under attack and sinking. The Allies were having remarkable success in the battle surrounding convoy ONS-5. It was a disturbing new development.
Spotting a very large convoy on the 12th May they were forced to crash dive several times by aircraft that appeared to be accompanying the convoy. Then an aircraft dropped a smoke flare and yellow dye to mark their position as they crash dived again. Now they received the undivided attention of the convoy escort destroyers and corvettes.
Late on the 12th a second group of ships took over the attack. Herbert A. Werner, the Executive Officer on U-230 was to write a memorable account of the subsequent hours:
20.00: The new group launched its first attack, then another, and another. We sat helpless 265 metres below. Our nerves trembled. Our bodies were stiff from cold, stress, and fear. The mind-searing agony of waiting made us lose any sense of time and any desire for food. The bilges were flooded with water, oil, and urine.
Our washrooms were under lock and key; to use them then could have meant instant death, for the tremendous outside pressure would have acted in reverse of the expected flow. Cans were circulated for the men to use to relieve themselves. Added to the stench of waste, sweat, and oil was the stink of the battery gases. The increasing humidity condensed on the cold steel, dropped into the bilges, dripped from pipes, and soaked our clothes.
By midnight, the Captain realized that the British would not let up in their bombardment, and he ordered the distribution of potash cartridges to supplement breathing. Soon every man was equipped with a large metal box attached to his chest, a rubber hose leading to his mouth, and a clamp on his nose. And still we waited.
Over 200 canisters had detonated above and around us by 01.00. Several times we had used a ruse in an effort to escape. Through an outboard valve, we repeatedly expelled a great mass of air bubbles. These screens of air floated away on the current, reflecting the Asdic impulses like a large solid body. But our attackers were fooled into chasing the decoys only twice, and both times they left at least one vessel behind, directly over our heads. Unable to sneak away, we gave up the game and concentrated on conserving our power, our compressed air, and our dwindling supply of oxygen.
04.00: The boat had fallen to 275 metres. We had been under assault for twelve hours and there was no sign of relief This day was my birthday and I wondered whether it would be my last. How many chances could one ask for?
08.00; No lessening of the attacks. The water in the bilges rose above the deck plates and splashed around my feet. The bilge pumps were useless at this depth. Whenever a charge erupted, the Chief released some compressed air into the tanks to assure the boats buoyancy.
12.00: The boat’s down angle had sharply increased. Our compressed-air supply was dangerously low, and the boat slipped ever farther away.
20.00: The air was thick, and even more so as we breathed it through the hot cartridges. The Devil seemed to be knocking on our steel hull as it creaked and contracted under the enormous pressure.
22.00: The barrage increased in violence as dusk closed in on the surface. Wild attacks at shorter intervals indicated that the enemy had lost his patience.
By midnight, we had approached the limit for boat and crew. We had reached a depth of 280 metres and the boat was still sinking. I dragged myself through the aisle, pushing and tossing men around, forcing them to stay awake. Whoever fell asleep might never be awakened.
03.10: A thunderous spread rattled down, but without effect. We were closer to being crushed by the mounting pressure than by the exploding canisters. As the echo of the last blast slowly subsided, something else attracted our attention. It was the thrashing of retreating propellers. For a long time we listened to the fading sound, unable to believe that the Tommies had given up the hunt.
04.30: For over an hour there was silence. We spent all that time doubting our luck. We had to make sure, so we turned on our fresh-water producer, went high with the motors. No reaction from above.
Using the last of our compressed air and battery power, the Chief managed to lift the overloaded boat, metre by metre. Then, unable to slow her upward movement, Friedrich let her rise freely and yelled, ‘Boat rises fast fifty metres boat has surfaced!‘ U-230 broke through to air and life.
We pushed ourselves up to the bridge. Around us spread the infinite beauty of night, sky, and ocean. Stars glittered brilliantly and the sea breathed gently. The moment of rebirth was overwhelming. A minute ago, we could not believe that we were alive; now we could not believe that death had kept his finger on us for thirty-five gruesome hours..