During one of the pre D-day practice landings at Slapton Sands German E-Boats got through the Destroyer screen and sank the Transport Libreville with 800 US troops on board.
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The assault at Slapton Sands was known as Exercise Tiger, one of several rehearsals conducted in preparation for the momentous invasion to come. So vital was the exercise of accustoming the troops to the combat conditions they were soon to face that commanders had ordered use of live naval and artillery fire, which could be employed because British civilians had long ago been relocated from the region around Slapton Sands. Individual soldiers also had live ammunition for their rifles and machine guns.
In those early hours of 28 April off the south coast in Lyme Bay, a flotilla of eight LSTs (landing ship, tank) was plowing toward Slapton Sands, transporting a follow-up force of engineers and chemical and quartermaster troops not scheduled for assault but to be unloaded in orderly fashion along with trucks, amphibious trucks, jeeps and heavy engineering equipment.
Out of the darkness, nine swift German torpedo boats suddenly appeared. On routine patrol out of the French port of Cherbourg, the commanders had learned of heavy radio traffic in Lyme Bay. Ordered to investigate, they were amazed to see what they took to be a flotilla of eight destroyers. They hastened to attack.
German torpedoes hit three of the LSTs. One lost its stern but eventually limped into port. Another burst into flames, the fire fed by gasoline in the vehicles aboard. A third keeled over and sank within six minutes.
There was little time for launching lifeboats. Trapped below decks, hundreds of soldiers and sailors went down with the ships. Others leapt into the sea, but many soon drowned, weighted down by water-logged overcoats and in some cases pitched forward into the water because they were wearing life belts around their waists rather than under their armpits. Others succumbed to hypothermia in the cold water.
When the waters of the English Channel at last ceased to wash bloated bodies ashore, the toll of the dead and missing stood at 198 sailors and 551 soldiers, a total of 749, the most costly training incident involving U.S. forces during World War II.
Allied commanders were not only concerned about the loss of life and two LSTs -- which left not a single LST as a reserve for D-Day -- but also about the possibility that the Germans had taken prisoners who might be forced to reveal secrets about the upcoming invasion. Ten officers aboard the LSTs had been closely involved in the invasion planning and knew the assigned beaches in France; there was no rest until those 10 could be accounted for: all of them drowned.
A subsequent official investigation revealed two factors that may have contributed to the tragedy -- a lack of escort vessels and an error in radio frequencies.
Although there were a number of British picket ships stationed off the south coast, including some facing Cherbourg, only two vessels were assigned to accompany the convoy -- a corvette and a World War I-era destroyer. Damaged in a collision, the destroyer put into port, and a replacement vessel came to the scene too late.
Because of a typographical error in orders, the U.S. LSTs were on a radio frequency different from the corvette and the British naval headquarters ashore. When one of the picket ships spotted German torpedo boats soon after midnight, a report quickly reached the British corvette but not the LSTs. Assuming the U.S. vessels had received the same report, the commander of the corvette made no effort to raise them.
Whether an absence of either or both of those factors would have had any effect on the tragic events that followed would be impossible to say -- but probably not. The tragedy off Slapton Sands was simply one of those cruel happenstances of war.
Meanwhile, orders went out imposing the strictest secrecy on all who knew or might learn of the tragedy, including doctors and nurses who treated the survivors. There was no point in letting the enemy know what he had accomplished, least of all in affording any clue that might link Slapton Sands to Utah Beach.
Nobody ever lifted that order of secrecy, for by the time D-Day had passed, the units subject to the order had scattered. Quite obviously, in any case, the order no longer had any legitimacy particularly after Gen. Eisenhower's Supreme Headquarters, Allied Expeditionary Force, in July 1944 issued a press release telling of the tragedy. Notice of it was printed, among other places, in the soldier newspaper, Stars & Stripes.