Kapitänleutnant Hans-Joachim Rahmlow had joined the Kriegsmarine in 1928, and had served nearly all of his career in coastal artillery. However around November 1940 he first set foot on a submarine. His first boat had no patrols under his leadership and he moved to U-570 in May 1941. U-570 was a brand new build Type VIIC U-boat, on her commission date KptLt Rahmlow took command. In August U-570 was ordered to take part in an operation to sink a concentration of allied shipping in the Atlantic.
Plan of U-570
The Icelandic Gap is the stretch of water between Iceland and the UK. It's a strategic position, during the cold war it was the Royal Navy and RAF's main duty to seal this gap and keep Russian forces, especially submarines, bottled up and out of the Atlantic. The same applied in the Second World War, if the British could close this location, then the Kriegsmarine would be contained and unable to get at the supply convoys crossing the Atlantic. In late August 1941 U-570 tested her mettle against the formidable forces arrayed against her.

The weather, as it often is in the Atlantic, was horrific. Four days into her patrol (August 27th) the seas had battered the submarine and most of her crew were seasick. In addition she'd been attacked by a RAF Hudson bomber from 269 Squadron in Iceland, however during the attack run the bombers depth bombs had failed to release, allowing U-570 to escape. So KptLt Rahmlow ordered the morning to be spent submerged. At about 1050 she re-surfaced to face the battering of the sea.
U-570 in heavy seas, you can see the waves over the deck.
Many miles away in the grey stormy sky another Hudson bomber was pitching in the storm. On its sides were the code letters B-L, it was another plane from 269 Squadron, piloted by Squadron Leader James Thompson. Sqn Ldr Thompson had been called to assist the other Hudson after its earlier aborted attack. Suddenly a blip appeared, at a range of 14 miles, on the airborne radar. Sqn Ldr Thompson set up his approach run.

On the U-570 KptLt Rahmlow suddenly heard over the stormy weather the sound of aircraft engines. He immediately ordered a crash dive. Bursting out of the grey mist the Hudson hurtled towards the rapidly submerging submarine. Just as U-570 became fully waterlogged, Sqn Ldr Thompson released his four 250lb depth bombs in a line. They were all fused to detonate at fifty feet. One of the charges detonated just ten metres from the bow, the blast smashed into the bow of the submarine and crumpled it and shorted out the electrics. In the dark and confusion inside the metal coffin it's possible the blast may have knocked KptLt Rahmlow unconscious. The engine room crew suddenly scrambled forward yelling warnings about chlorine gas escaping. The next sound the crew heard was the clang of the watertight doors to the engine room being slammed shut. With no way to get the power back, in darkness and with the risk of choking on chlorine the crew blew ballast and surfaced. They tumbled out of the hatches to man the anti-aircraft guns and fight off the Hudson.

Sdn Ldr Thompson saw the U-570 sitting in a pool of bubbles and froth from his depth bomb and the subsequent surfacing. He turned towards her and the nose gunner fired a burst from his machine gun at the submarine. On board U-570 the crew quickly found that with the pitching of the sea and the submarine it was impossible to lay their AA weapons on the circling bomber. Expecting another stick of bombs at any second they quickly hoisted a flag of surrender.

The Surrender, the flag can just be seen
As the Hudson circled over them the crew destroyed their radio and code books, but beforehand they sent a final message stating "Am not able to dive, and am being attacked by aircraft." This was the last the Kriegsmarine would hear from U-570. They did try to send another submarine to support U-570, however allied action meant she had to remain submerged and couldn't reach the area. Overhead the Hudson radioed for support and was joined shortly by another Hudson which had been en-route to Scotland, and about three hours later by a Catalina flying boat. As the Hudson's ran out of fuel the Catalina was left orbiting the submarine. She had orders that if no allied ships reached the scene by darkness then she was to order the crew off the boat and sink U-570. However it seems the Catalina failed to carry out these orders, as at around 10 pm an anti-submarine trawler arrived on scene and was guided in by flares dropped by the Catalina. With the submarine safely in the possession of the Royal Navy the Catalina returned to base.
The trawler, HMT Northern Chief, informed the Germans that any attempt to scuttle, submerge or any other action not ordered by the trawler would be met with gunfire, and the crew would not be rescued. Overnight several other vessels including two destroyers reached the area.
The next morning a seaplane from 330 Squadron reached the area, spotting the submarine and trawler the Norwegian pilots launched an attack on the U-570 and strafed the HMT Northern Chief, which promptly returned fire. Luckily one of the destroyers saw what was happening and ordered the plane away.
Boarding action!
Using a Carley float three sailors boarded the U-570, and attached a tow rope. The Germans were then transferred off the boat to another trawler and one of the destroyers. The U-570 was then towed by the flotilla to Iceland with a constant stream of aircraft overhead for cover. She was beached around August 30th at Þorlákshöfn.
U-570 on the beach
U-570 was later used for a number of tests and research, she also gave up a few secrets in submarine design which the allies had not yet worked out, such as rubber mountings for the U-boats engines. These meant less noise was transmitted to the hull, making her quieter.
After these tests she was renamed HMS Graph (G for "German" and from the German word Graf) and entered service with the Royal Navy conducting two war patrols. Although she made several attacks, including one on an enemy submarine she failed to score any hits. Eventually lack of replacement supplies meant she was decommissioned and used for target trials of depth charges. After resisting the battering she was sold for scrap, but broke free of the tow rope used to send her to the breaker's yard. Her hulk came to rest on Coul Point, on the west coast of Islay. She remains there to this day.

Of the people involved, the crew of the 269 Squadron Hudson, Sqn Ldr Thompson and Flying Officer Coleman (the Hudson's Bomber/Navigator), each received the Distinguished Flying Cross. KptLt Rahmlow remained a POW and died on 13th of June 1967.

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