Troops coming ashore at Slapton Sands during Exercise Tiger. (Credit: NARA)

In the early morning hours of April 28, 1944, an Allied fleet slinked toward the coast of southern England. Along with a lone British corvette, the flotilla included eight American tank landing ships, or LSTs, each one of them filled to the brim with soldiers from the U.S. Army’s VII Corps. In just five weeks, these same troops were scheduled to land in France as part of Operation Overlord, the Allies’ secret plan to invade Nazi-held Western Europe. Overlord was integral to the Allied strategy for victory in World War II, and to ensure it went smoothly, military brass had organized a sweeping dress rehearsal codenamed “Exercise Tiger.” Before they stormed Utah Beach on D-Day, the men of VII Corps would get in a practice run at Slapton Sands, a picturesque British seafront that bore a striking resemblance to the coast of Normandy.

Exercise Tiger had begun six days earlier, when some 23,000 G.I.s assembled at staging areas in England. After putting to sea just as they would on D-Day, the men circled back for a series of simulated landings on the Devon seacoast, which was dressed up to resemble a warzone. The secluded beach at Slapton Sands had been converted into a maze of mines, barbed wire and concrete obstacles, and the nearby civilian population had been evacuated from their villages. To give the soldiers a taste of the chaos of battle, the British Royal Navy planned to shell the beach with live fire until just moments before the American troops made their mock landing.

Lyme Bay, England. (Credit: Steinsky/Wikimedia Commons)

Supreme Allied Commander Dwight D. Eisenhower was on hand to watch the exercise unfold, but its first wave was plagued by delays and miscommunications. On April 27, a scheduling foul-up had even seen a few of the American Higgins boats land on the beach in the midst of the British Navy’s bombardment. The shelling was quickly called off, but not before the American forces suffered several friendly fire casualties.

Eisenhower and the rest of the officers were hoping for a more orderly landing on April 28, when VII Corps’ second wave of engineers and back-up troops approached the coast in a convoy of eight landing ships. Until then, there had been no threat of enemy intervention in the exercise, but as the flotilla steamed through Devon’s Lyme Bay, it caught the attention of nine German “Schnellboote,” or “fast boats.” Known as “E-boats” to the Allies, these small, nimble raiders were outfitted with torpedoes and 40mm guns. Upon discovering that an Allied fleet was in the region, they immediately sped to intercept it.

Troops coming ashore Slapton Sands during the exercise. (Credit: NARA)

It was around 1:30 a.m. when the German E-boat attack began. As the eight American LSTs lumbered toward the coast, their crews were startled by an eruption of gunfire and the flash of tracer rounds in the night sky. “All hell broke loose,” one American sergeant remembered. The flotilla was caught completely off guard. British forces had been monitoring the approach of the E-boats, but due to an error, they were operating on a different radio frequency than the Americans. To make matters worse, the landing ships’ main escort, a British destroyer called the Scimitar, had sustained damage earlier in the evening and returned to port for repairs. When the shooting started, their only protection was a 200-foot corvette called the Azalea.

The Allies’ confusion turned to panic shortly after 2 a.m., when a German E-boat torpedo careened into the side of an American landing ship called LST-507. Lieutenant Gene Eckstam, a medical officer who was aboard the ship, described hearing “a horrendous noise accompanied by the sound of crunching metal and dust everywhere.” The explosion set the LST ablaze, killing dozens of troops and forcing others to abandon ship. “The assistant navigator and I jumped over the side of the LST into the near freezing water 25 feet below,” radio operator Steve Sadlon later wrote in an account of the attack. “The sea around the ship was covered with an oil slick from the badly damaged LST, and the surface was on fire.”

Troops on Slapton Sands beach during the exercise. (Credit: Library of Congress)

While LST-507 burned, another landing ship called LST-531 was hit by two torpedoes in quick succession and consumed in a ball of flames. As its crew hurled themselves overboard, a fourth torpedo plowed into LST-289, turning its stern into a mangled hulk. LST-289 would manage to stay afloat in spite of its damage, but LST-507 and LST-531 both sank within a matter of minutes. The survivors of the wrecked landing ships huddled in life rafts or floated helplessly in the chilly waters of Lyme Bay. Having not received proper instruction in the use of their lifejackets, many drowned under the weight of their bulky combat gear.

The Allied fleet had scattered and steamed toward the shore during the attack, but once the German E-boats retreated, a lone LST and a British destroyer returned to the scene and began plucking survivors out of the water. By then, hundreds had either drowned or succumbed to hypothermia. The rescuers would recall seeing a mass of dead soldiers bobbing in the bay. “We started stacking bodies on the deck,” veteran Wendell Hoppler later told the Sun-Sentinel newspaper. “We were too busy to stop and think about it. It was very impersonal. But you kept thinking, ‘Thank God it`s not me.’”

The losses from the disaster eventually totaled 749 American sailors and soldiers killed and several hundred more injured, yet they were not immediately made public. With Operation Overlord still looming, the Allies temporarily kept the debacle under wraps out of fear that it might tip off the Germans. They even considered scrapping the Normandy invasion until the bodies of several officers with direct knowledge of the attack were recovered from the bay. The survivors, meanwhile, were threatened with court martial if they spoke of the tragedy to anyone.

Exercise Tiger was the U.S. military’s deadliest training incident during World War II, but it did provide some useful intelligence. In the wake of the ambush, the Allies revamped their radio communications procedures and ensured that their troops were fully trained in the use of their lifejackets. Armed with this new knowledge, American forces would later invade France on June 6, 1944—D-Day. The Army’s VII Corps suffered a few hundred casualties in storming Normandy’s Utah Beach, but looking back, some of its veterans would say that the Exercise Tiger dry run had been even more terrifying. “In comparison to the E-boat attack, Utah Beach was a walk in the park,” Steve Stadlon told NBC News in 2009.

The U.S. military publicly acknowledged the losses of Exercise Tiger in the months after D-Day, but the story was overshadowed by news of the Allied invasion of Western Europe, and it remains little known even today. One of the few reminders of the incident is located at Slapton Sands, where a salvaged Sherman tank sits as a monument to the 749 servicemen who lost their lives in the nearby bay.