On Aug. 27, 1941 Lockheed Hudsons of RAF Coastal Command’s 269 Squadron performed a remarkable mission, something never repeated during the war: they captured a U-boat unassisted by surface ships.

At the start of World War II, few thought the U-boat would be as devastating as it proved to be. But convoys and sonar-equipped escorts soon proved inadequate to defend the Allies’ merchantmen, and the RAF’s only offensive weapon was the anti-submarine warfare aircraft. For RAF Coastal Command, the first two years of the war were the hardest.

Although starved of resources, operating with outdated aircraft and often useless weaponry, they were still the only force that could take the fight to the U-boats as demonstrated on Aug. 27, 1941 when Lockheed Hudsons of 269 Squadron performed a remarkable mission, something never repeated during the war: they captured a U-boat unassisted by surface ships.

U-570 was on its first war patrol. As told by Mark Lardas in his book Battle of the Atlantic 1939-41, the U-boat was three days out of Trondheim and everything was going wrong. The air compressor was malfunctioning. The diesels were not tuned, causing unpleasant vibrations. The hydrophones (passive listening gear) had been knocked out after U-570 bottomed out heading to Trondheim. Plus the crew was seasick. A seasick sailor in a crowded U-boat, vomiting into buckets around your close-packed crewmates, was a good way to get everyone else seasick.

It surfaced at 1050hrs, just as a patrolling Hudson was overhead and attacked it with depth charges. The attack was ferociously noisy, but did not seriously damage U-570. Its crew was green and seasick, however, and its captain, Hans-Joachim Rahmlow, inexperienced. Both now panicked. Convinced the forward part of the ship was filling with chlorine gas, from seawater mixing with battery acid, the crew sealed off the bow and the captain ordered the ship to surface and be abandoned. The crew quickly crowded onto the deck and conning tower.

RAF Coastal Command Lockheed Hudson.

Unwilling to plunge into the freezing Icelandic water, and being strafed by the Hudson which originally attacked it, U-570 surrendered, the crew waving white shirts and boards. The pilot of the Hudson ceased fire, calling other aircraft to join him. These included another Hudson (armed with depth charges) and a Consolidated Catalina from 209 Squadron which sank U-452 two days earlier. U-570’s skipper sent out an uncoded radio message for help, and had the U-boat’s secret equipment pitched overboard. This included the Enigma code machine.

In response to this radio call, U-boats and surface ships rushed to the scene. The swarm of aircraft kept the U-boats away, and an armed trawler arrived at 2200hrs, near sunset, and took possession of the prize. Despite an attack by a Norwegian-manned Northrup unaware it had been surrendered the next morning, the British managed to bring U-570 safely to Reykjavik.

While the secret papers and Enigma machine were gone, U-570 proved an intelligence bonanza, providing a wealth of information about the Type VII submarine. Nor was the destruction of its Enigma machine a loss. Britain already had one, taken from U-110, captured by surface warships. U-110’s crew was unaware the Enigma machine had been seized, the boat having sunk under tow to Iceland after its secret equipment had been removed.

U-570’s capture could not be concealed, so having its skipper radio its code equipment had been destroyed kept the Germans from realizing their Enigma code had been cracked and the British were reading it. Eventually, after operation testing ended, U-570 was commissioned into the Royal Navy as HMS Graph, spending the rest of its active career hunting U-boats.

The German U-Boat U-570 enters dock at Barrow-in-Furness after its capture.

Battle of the Atlantic 1939-41 is published by Osprey Publishing and is available to order here.

Photo credit: Crown Copyright