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Hitler's Nightmare: This Is How the Allies Hunted down Nazi Submarines

September 20, 2019 Topic: History Region: Europe Blog Brand: The Buzz Tags: World War IISubmarinesBay Of BiscayNazi GermanyU.S. NavyRAF

Hitler's Nightmare: This Is How the Allies Hunted down Nazi Submarines

The inside story.

More top-secret antisubmarine devices in development included the Magnetic Anomaly Detector (MAD), which recorded variations in the Earth’s gravitational field caused by a submerged U-boat. An air-dropped sonar sensor called the sonobuoy showed great promise, as did an acoustic homing torpedo nicknamed Zombie. But the sub hunters’ most effective technological breakthrough was also the most highly classified: ULTRA, the decryption of German military signal ciphers.

Thanks to ULTRA, Allied codebreakers could read nearly every order that Admiral Dönitz gave to his U-boat commanders. Consequently, Coastal Command knew when enemy submarine traffic in the Bay of Biscay was likely to increase. Further, a chain of radio receivers called Huff-Duff (which stood for High Frequency Direction Finding, or HF/DF) helped triangulate a U-boat’s location to within a few miles whenever it broke radio silence to report in or request orders.

Initially, production delays and reliability issues limited the effectiveness of these new weapons. By June 1942, only five Vickers Wellington bombers had been fitted with Leigh Lights, and British-built Mark III centimetric radar would not appear until March of the following year. Worse still, Air Chief Marshal Joubert’s Bay Offensive was in danger of collapsing due to an inadequate number of long-range, radar-equipped patrol bombers. In 1941, RAF Coastal Command warplanes managed to sink just one U-boat in the Bay of Biscay. By the end of 1942, that number climbed to a mere seven submarines killed for thousands of flight hours spent patrolling the bay.

If Coastal Command did not yet possess suitable sub-hunting aircraft, there was an organization that did. The USAAF Antisubmarine Command began to receive in the autumn of 1942 factory-new B-24D Liberator bombers specially equipped to combat U-boats. Fitted with SCR-517 ASV radar, radio altimeters, and long-range navigational equipment, these aircraft were badly needed to reenergize Air Marshal Joubert’s Bay Patrol. It would, however, take British Prime Minister Winston Churchill’s personal intervention to get them into the fight.

Bringing the USAAF To St. Eval

Writing to Harry Hopkins, President Roosevelt’s personal emissary, Churchill asked for a force of USAAF Liberators equipped with microwave radar to work with Coastal Command against U-boats in the Bay of Biscay. Roosevelt deferred the question to General Dwight D. Eisenhower, then commanding Allied forces in North Africa. Ike agreed to Churchill’s request with one caveat: that he reserved the authority to transfer USAAF antisubmarine aircraft from England to Mediterranean bases at any time. Starting on November 6, 1942, U.S.-marked sub-hunter B-24s started winging their way across the Atlantic Ocean toward Great Britain.

Just getting there proved no easy task. While the first three Liberators crossed without incident, ferocious winter storms battered another flight of six planes so badly that five of them had to turn back. One B-24 disappeared without a trace, while the remaining four regrouped to make an arduous but safer journey along the South America-Africa-England route. By November 27, the 1st Antisubmarine (A/S) Squadron occupied its new home, RAF Station St. Eval in Cornwall. Its sister unit, the 2nd A/S Squadron, would arrive in early January.

Conditions at St. Eval proved less than ideal. First, no one knew the Americans were coming. Living and working conditions were Spartan; wartime RAF rations of brussels sprouts and cabbage were described by one USAAF airman as “unbelievably bad,” while gloomy English weather made staying warm a constant struggle. Compounding matters, St. Eval’s ramps and parking areas were already clogged by three squadrons of Coastal Command bombers as well as other RAF aircraft. No hangars existed for maintenance, so mechanics had to work outside. Darkness came early, as did winter winds that numbed the ground crews struggling to keep their planes operational.

Equally challenging was St. Eval’s distance from U.S. supply depots. Couriers drove all day to reach the nearest USAAF warehouse, which may or may not have had on hand the required replacement part. The newly arrived sub-hunter outfits also lacked trained radar repair specialists, postal clerks, and other administrative staff necessary to keep a flying squadron running smoothly. Eighth Air Force lent the A/S units some 66 support personnel until their own ground echelons landed in mid-January.

 

Readying the American Flyers For Combat

The 1st and 2nd Antisubmarine Squadrons quickly adapted to Coastal Command’s tactics and procedures. The Americans learned they would operate under No. 19 Group, flying missions of 10 to 11 hours in duration out to the Bay of Biscay and back. Veteran British aircrews advised the novice sub hunters on how best to approach a wily U-boat, using low cloud cover or the sun to avoid observation. The RAF also warned their USAAF colleagues about a dangerous new threat, long-range Junkers Ju-88 fighters that had been spotted over the bay recently.

 

After a brief settling-in period, USAAF Liberators began flying operational patrols on November 16. The Americans’ first attack on a U-boat took place on December 29, when Captain Douglas Northrop dropped 12 250-pound depth charges on a rapidly submerging sub. That vessel escaped unscathed from Northrop’s strike, as did another U-boat attacked by Lieutenant Walter Thorne’s B-24 two days later. In both cases, the U-boats were detected by ASV radar but managed to crash dive under a barrage of aerial explosives.

January was spent readying the 2nd A/S Squadron for combat. Also that month the 1st Antisubmarine Group (Provisional) was organized with Lt. Col. Jack Roberts (formerly of the 1st A/S Squadron) taking command. The group received administrative support from the USAAF’s England-based VIII Bomber Command but took operational direction from RAF Coastal Command’s No. 19 Group.

Operation Gondola

Coastal Command had big plans for the American sub hunters. From February 6-15, 1943, the Liberators participated with other No. 19 Group warplanes in Operation Gondola, a high-density patrol over the Biscayan approaches. Intelligence suggested that during this period the Bay of Biscay would be filled with as many as 40 U-boats, all unprepared for the long-legged B-24s and their powerful new radar. Ranging far out into the bay, these U.S. Liberators were likely to surprise the enemy in areas they previously believed were safe from air attack.

This new tactic paid off immediately. On February 6, 1st Lt. David Sands caught a U-boat on the surface but overshot the target in his excitement and missed. Sands then made a second pass but managed to drop only two depth charges due to jammed bomb racks. Three days later, another B-24 piloted by 1st Lt. Emmett Hunto dove on a submarine too late. Hunto’s ordnance detonated behind the rapidly submerging boat, which survived unscathed.

February 10 saw several attacks made by 2nd A/S bombers. First Lieutenant John Kraybill pressed in three times on a sub despite heavy antiaircraft fire, only to be frustrated by malfunctioning bomb racks. Lieutenant William Sanford’s Liberator, nicknamed Tidewater Tillie, enjoyed better luck. Catching an unwary U-boat off the Spanish coast later that same morning, Sanford dropped nine 250-pound depth charges on it in three passes. The German submarine was last seen settling by its stern, followed shortly by a large dome-shaped bubble of air rising to the surface. Admiralty officials scored the boat as “probably sunk,” later upgraded to a confirmed kill after ULTRA intercepted German reports indicating U-519 had disappeared in that region without a trace. The USAAF received its first credited sinking of the campaign.

Recent research indicates that Lieutenant Sanford’s crew actually struck U-752 on its way home from operations in the North Atlantic, inflicting minor damage. The fate of U-519 remains unexplained.

Operation Gondola showed what radar-equipped antisubmarine aircraft could do when employed in a maximum effort saturation campaign. During this 10-day surge Allied patrol planes logged 2,260 hours over the bay, resulting in 18 sightings and seven attacks. American B-24s accounted for 72 percent of all U-boat detections and 57 percent of attacks made, with Sanford’s strike on February 10 marking Gondola’s one credited kill.

The USAAF Withdraws From Biscay Operations

Coastal Command’s newly appointed commander, Air Marshal John Slessor, appreciated what these capable U.S.-crewed Liberators could do. Therefore, he was shocked when in March the 1st A/S Group unexpectedly pulled out of St. Eval. For their part, USAAF commanders understood that the sub hunters’ time in England would be temporary—they determined the U-boat threat in North Africa took priority over Coastal Command’s requirements and transferred their most combat-tested A/S outfit to Morocco in response.

This abrupt reassignment deprived Slessor of a powerful asset just as his spring offensives, codenamed Enclose and Derange, were gaining momentum. No. 19 Group would have to carry on solely with British and Commonwealth air units, now receiving new Leigh-Light Wellingtons and four-engined Handley Page Halifax bombers equipped with centimetric Mark III radar sets. In March a squadron of British-marked antisubmarine Liberators also began flying out of St. Eval.

The coming of spring brought both milder weather to the North Atlantic and a corresponding increase in Allied convoy activity. As Admiral Dönitz’ submarines sortied out to strike those convoys, so did Air Marshal Slessor’s maritime patrol aircraft scramble to meet them over the Bay of Biscay’s constricted waters. British bombers sank one boat in March, two more during April, and an impressive seven subs caught transiting the bay during the height of operations in May.