In April 1944, the Allied military staged Exercise Tiger, a full-scale dress rehearsal for the upcoming Normandy landings, at Slapton Sands in Devon, England. Thousands of American troops boarded Landing Ships, Tank (LSTs) to practice amphibious assaults under live-fire conditions. To ensure absolute secrecy, strict radio silence was enforced.
However, a fatal flaw was introduced before the ships even left port: a simple clerical typo on the communications schedule. The British Royal Navy escort headquarters and the American LST convoy were inadvertently assigned different radio frequencies due to a mismatch in distributed signal manuals. When the primary British escort ship, HMS Scimitar, suffered collision damage and left the convoy for repairs, the remaining replacement escort, HMS Saladin, was unable to establish radio contact with the American ships.
Unbeknownst to the American LSTs, nine German E-boats—fast torpedo vessels—were actively prowling Lyme Bay that night. British shore radar spotted the enemy patrol and frantically transmitted warnings to the convoy, but because the Americans were tuned to the wrong frequency, the messages were never received. In the early morning hours of April 28, 1944, the German E-boats struck the unsuspecting, convoy, sinking two LSTs and heavily damaging a third.
The resulting chaos, cold water, and improperly used lifejackets led to the deaths of 749 American soldiers and sailors in a matter of minutes—a higher casualty count than was suffered by the same units during the actual D-Day invasion of Utah Beach. The tragedy was promptly classified to prevent leaks regarding invasion plans, making this mistyped radio schedule one of the most devastating administrative errors of World War II.