Exercise Tiger Exercise Tiger , or Operation Tiger , was the code name for one in a series of large - scale rehearsals for the D - Day invasion of Normandy , which took place on Slapton Sands or Slapton Beach in Devon . Coordination and communication problems resulted in friendly fire deaths during the exercise , and an Allied convoy positioning itself for the landing was attacked by E - boat s of the German Kriegsmarine , resulting in the deaths of 946 American servicemen . The incident was under the strictest secrecy at the time due to the impending invasion , and was only nominally reported afterward ; as a result it has been called " forgotten " . Exercise . Landing Operations . In late 1943 , as part of the build - up to D - day , the British Government set up a training ground at Slapton Sands , Devon , to be used by Force " U " , the American forces tasked with landing on Utah beach . Slapton Beach was selected for its similarity to Utah Beach : a gravel beach , followed by a strip of land and then a lake . Approximately 3 , 000 local residents in the area of Slapton , now South Hams District of Devon , were evacuated . Some had never left their villages before being evacuated . Landing exercises started in December 1943 . Exercise Tiger was one of the larger exercises that would take place in April and May 1944 . The exercise was to last from 22 April until 30 April 1944 , and covered all aspects of the invasion , culminating in a landing at the Slapton Sands beach . On board nine large tank landing ship s ( LSTs ) , the 30 , 000 troops prepared for their mock beach landing . The landing also included a live - firing exercise . Protection for the exercise area came from the Royal Navy . Two destroyer s , three Motor Torpedo Boat s and two Motor Gun Boat s patrolled the entrance to Lyme Bay and Motor Torpedo Boats watched the Cherbourg area where German E - boat s were based . The first phase of the exercise focused on marshalling and embarkation drills , and lasted from 22 to 25 April . On the evening of 26 April the first wave of assault troops boarded their transports and set off , the plan being to simulate the Channel crossing by taking a roundabout route through Lyme Bay , in order to arrive off Slapton at first light on 27 April . Friendly fire incident . The first practice assault took place on the morning of 27 April and was marred by an incident involving friendly fire . H - hour was set for 7 : 30 am , and was to be preceded by a live firing exercise to acclimatize the troops to the sights , sounds and even smells of a naval bombardment . During the landing itself , live rounds were to be fired over the heads of the incoming troops by forces on land , for the same reason . This followed an order made by General Dwight D . Eisenhower , the Supreme Allied Commander , who felt that the men must be hardened by exposure to real battle conditions . The British heavy cruiser was to shell the beach with live ammunition , from H - 60 to H - 30 ( i . e . 6 : 30 to 7 : 00 am ) giving the beachmasters half an hour to inspect the beach and declare it safe . Several of the landing ships for that morning were delayed , and the officer in charge decided to delay H - hour for 60 minutes , until 8 : 30 . This message was received by " Hawkins " , but not by a number of the landing craft , with the result that troops were landing on the beach at the same time as the bombardment was taking place . British Marines on one vessel recorded in its log book ( the only log which has since been recovered from any of the boats ) that men were being killed by friendly fire . " On the beaches they had a white tape line beyond which the Americans should not cross until the live firing had finished . " But the American soldiers said they were going straight through the white tape line and getting blown up . Battle of Lyme Bay . On the day after the first practice assaults , early on the morning of 28 April , the exercise was blighted when a convoy of follow - up troops was attacked by nine German E - boats in Lyme Bay . Of the two ships assigned to protect the convoy , only one was present . , a corvette was leading the nine LSTs in a straight line , a formation which later drew criticism since it presented an easy target to the E - boats . The second ship which was supposed to be present , HMS " Scimitar " , a World War I destroyer , had been in collision with an LST , suffered structural damage and left the convoy to be repaired at Plymouth . Because the LSTs and British naval headquarters were operating on different frequencies , the American forces did not know this . When other British ships sighted the E - boats earlier in the night and told the corvette , its commander failed to inform the LST convoy , assuming incorrectly that they had already been told . British shore batteries defending Salcombe Harbour had seen silhouettes of the E - boats but had been instructed to hold fire so the Germans would not find that Salcombe was defended . The E - boats left Cherbourg on patrol the previous evening and did not encounter the Allied patrol lines either off Cherbourg or in the Channel . They spotted the convoy ( convoy " T - 4 " ) , eight LSTs carrying vehicles and combat engineers of the 1st Engineer Special Brigade with a single corvette as escort , and then attacked . Aftermath . As a result of official embarrassment and concerns over possible leaks just prior to the real invasion , all survivors were sworn to secrecy by their superiors . Ten missing officers involved in the exercise had BIGOT - level clearance for D - Day , meaning that they knew the invasion plans and could have compromised the invasion should they have been captured alive . As a result , the invasion was nearly called off until the bodies of all ten victims were found . There is little information about how exactly individual soldiers and sailors died . Various eyewitness accounts detail hasty treatment of casualties and unmarked mass graves in Devon fields . Several changes resulted from mistakes made in Exercise Tiger : The casualty statistics from Tiger were not released until August 1944 along with the casualties of the actual D - Day landings themselves . There is little documentation in official histories about this tragedy . Some commentators have called it a cover - up , but the initial critical secrecy about Tiger may have merely resulted in longer - term quietness . In his book " The Forgotten Dead - Why 946 American Servicemen Died Off The Coast Of Devon In 1944 - And The Man Who Discovered Their True Story " , published in 1988 , Ken Small declares that the event " was never covered up ; it was ' conveniently forgotten ' " . Charles B . MacDonald , author and former deputy chief historian at the U . S . Army Center of Military History , notes that the incident was reported in a press release issued from the Supreme Headquarters , Allied Expeditionary Force , and appeared in the July issue of " Stars and Stripes " . In addition , the story was detailed in at least three books at the end of the war , including , Captain Harry C . Butcher ' s " My Three Years With Eisenhower " ( 1946 ) , and in several publications and speeches in the intervening years . MacDonald surmises that the press release went largely unnoticed in light of the larger events that were occurring at the time , the battle for France in the summer of 1944 , and the fact that they were just glad that the war was over in 1945 . Harison mentioned it in his official Army history of the war ( p . 270 ) and Samuel Eliot Morison also discussed it in his official Navy history , US Naval Operations , vol . 11 , p . 66 . Memorials to the victims . With little or no support from the American or British armed forces for any venture to recover remains or dedicate a memorial to the incident , Devon resident and civilian Ken Small took on the task of seeking to commemorate the event , after discovering evidence of the aftermath washed up on the shore while beachcombing in the early 1970s . In 1974 , Small bought from the U . S . Government the rights to a submerged tank from the 70th Tank Battalion discovered by his search efforts . In 1984 , with the aid of local residents and diving firms , he raised the tank , which now stands as a memorial to the incident . The local authority provided a plinth on the seafront to put the tank on , and erected a plaque in memory of the men killed . Small documents how the local villagers were of more assistance than either the US or UK military officials . Later the American military honored and supported him , when at the same time the UK military were snubbing his efforts . Small died of cancer in March 2004 , a few weeks before the 60th anniversary of the Exercise Tiger incident . In 2006 , the Slapton Sands Memorial Tank Limited ( a non - profit organization , one of whose directors is Small ' s son Dean ) are seeking to establish a more prominent memorial listing the names of all the victims of the attacks on Exercise Tiger .