Ambush at Sea: The GI Slaughter Before D-Day
Introduction
In the early hours of 28 April 1944, off England’s southern coast, a routine D-Day rehearsal spiraled into one of World War II’s deadliest training disasters. Exercise Tiger was designed to emulate the Utah Beach landings in Normandy, testing over 30,000 American troops and scores of landing ships. Instead, German fast attack E-boats intercepted the convoy in Lyme Bay, unleashing torpedoes that sank three Landing Ship Tanks (LSTs) and claimed nearly 750 American lives. Two days before Pearl Harbor veteran Rear Admiral Don P. Moon would warn, “Nothing in war goes as planned,” but few anticipated such carnage so close to home.
This article revisits that tragic night—its geography, unfolding drama, aftermath, and how it is remembered today. Map references pinpoint key locations, while museum and source citations guide further exploration into the “slaughter before D-Day.”
Map & Location Context
Lyme Bay and the adjacent Slapton Sands were chosen for their resemblance to Utah Beach: a wide, gently sloping shingle shoreline backed by dunes. Precise coordinates and grid references helped planners simulate Normandy’s terrain.
- Slapton Sands, Devon
– Ordnance Survey Grid: SX 825 445
– Latitude/Longitude: 50.2806° N, 3.6639° W - Lyme Bay Ambush Zone
– Approximate center: 50.2940° N, 3.6930° W
– Radius: 5 km from Slapton shoreline - Start Bay Evacuation Point
– OS Grid: SX 830 412
– Latitude/Longitude: 50.2490° N, 3.6720° W
These map references are displayed on navigational charts held by the National Maritime Museum and the Defence Geographic Centre in Taunton.
Prelude to Disaster
Operation Tiger was planned as a full-scale dress rehearsal for the Utah Beach assault, involving:
- 6 Landing Ship Tanks (LSTs) carrying infantry, vehicles, and fuel.
- 14 smaller landing craft (LCIs and LCTs) serving as control vessels.
- Escort by British Motor Torpedo Boats (MTBs) and Royal Navy destroyers.
A critical miscommunication arose when two destroyers were reassigned to counter a rumored U-boat threat, leaving the convoy lightly protected. Allied signals intelligence had intercepted German radio traffic hinting at E-boat patrols in the area, yet this warning failed to reach the LST captains. Troops aboard had undergone only basic drills in lifejacket inflation and abandonment procedures.
By 2100 hours on 27 April, nine LSTs and their escorts steamed from Torbay toward Slapton Sands for Section 1 landings. Radio silence was ordered to maintain D-Day secrecy, inadvertently preventing coordination when the first torpedo struck.
The Night of the Attack
Shortly after midnight, Kriegsmarine E-boats of the 5th Schnellboot-Flottille, operating from Cherbourg, vectored onto the unsuspecting convoy. Witness accounts and after-action reports highlight the following timeline:
- 00:15 – First sighting of fast-moving dark silhouettes on the radar scope of MTB-717.
- 00:22 – E-boat S-130 fires two torpedoes; both strike LST-507 amidships.
- 00:23 – Flames erupt aboard LST-507; hundreds of gallons of diesel fuel ignite the waterline.
- 00:30 – E-boats close in to launch a second salvo; LST-531 is hit and begins to sink.
- 00:35 – Friendly fire erupts as LST-515, in confused darkness, shoots at LST-496, mistaking her silhouette for a German vessel.
Ships were lost rapidly. Men, many unable to afford time to inflate lifejackets properly, succumbed to hypothermia and drowning in 10 °C water. Rescue craft, arriving only after dawn, pulled survivors from burning oil slicks.
Aftermath and Secrecy
By sunrise, three LSTs were sunk, two heavily damaged, and nearly 750 American soldiers dead or missing. The official Allied casualty report understated losses, citing 300 fatalities to preserve secrecy and morale ahead of the Normandy invasion.
Surviving officers were bound by security orders to withhold details; families received curt telegrams citing “miscellaneous naval accident.” Internal investigations criticized the reassignment of destroyers and poor communication of radar contacts. The true toll of Exercise Tiger remained classified until 1946, when declassified intelligence memos and oral histories revealed the scope of the disaster.
Importantly, ten officers privy to the Utah Beach plan were aboard LST-507 and LST-531. Had any been captured, the entire Overlord strategy risked compromise.
Museums and Memorials
Remembrance of Exercise Tiger has grown through dedicated exhibits and memorials. The following table summarizes key venues preserving the tragedy’s legacy:
| Museum / Memorial | Location | Highlights | Coordinates | Website |
|---|---|---|---|---|
| Slapton Sands Memorial (Tank Memorial) | Slapton Sands, Devon | WWII Sherman DD tank wreck; interpretive panels | 50.2806° N, 3.6639° W | https://defenceheritage.com/listings/the-sherman-tank-memorial/ |
| South Devon Area Museum | Totnes, Devon | Section on Exercise Tiger; oral history kiosk | 50.4322° N, 3.6830° W | https://southdevonareamuseum.co.uk/ |
| National Maritime Museum | Greenwich, London | Maps, naval logs, personal artifacts | 51.4810° N, 0.0077° W | https://www.rmg.co.uk/national-maritime-museum |
| US National D-Day Memorial | Bedford, Virginia, USA | Utah Beach exhibit; lists of Exercise Tiger dead | 37.4895° N, 79.4661° W | https://www.dday.org/ |
| Cherbourg Maritime Heritage Centre | Cherbourg-en-Cotentin, France | E-boat records; Kriegsmarine orders | 49.6336° N, 1.6194° W | https://cherbourgrenord.fr/heritage-centre |
Visiting these sites offers layered perspectives—from tactical naval operations to personal narratives of loss and survival. For other places of interest related to D-Day, check out the D-Day Centre, Fort Henry, the D-Day Story and Tyneham Village.
Conclusion
Exercise Tiger stands as a stark reminder that even meticulously planned operations can falter under war’s unpredictable forces. The tragedy at sea claimed more lives than some early Normandy engagements, yet remained obscured for decades. Today’s memorials and museums bring long overdue recognition to the young GIs who perished in training for the greatest amphibious assault in history. By retracing those dark hours through maps, artifacts, and first-person accounts, we honor their sacrifice—and ensure that the “slaughter before D-Day” is never forgotten.
Source References
- Small, Ken. The Forgotten Dead: Why 946 American Servicemen Died off the Coast of Devon in 1944 and the Man Who Discovered Their True Story. Atlantic Books, 2014.
- BBC Archive. “Exercise Tiger – The D-Day Rehearsal That Turned Tragic.” BBC History Online, April 2014.
- United States Army Center of Military History. Exercise Tiger Summary. CMH Publication, 1994.
- National Maritime Museum. LST-507 Action Report, ADM 199/23/45, The National Archives (UK).
- Oral History Interview with Pvt. James “Jim” Harper, US Army Signal Corps, 1978. Library of Congress Veterans History Project.
Photo credit: Stephen and Helen Jones