That was my recollection as well . . . I just did some Google searches, and here's one comment relating to why the disaster was covered up almost immediately:
"Nobody knows for certain how many U.S. soldiers and sailors died in the so-called Battle of Slapton Sands. It was a top-secret operation. General Eisenhower feared that if German intelligence learned the details of the mock invasion, he might have to postpone or even cancel D-Day."
The English press does tend to be overly dramatic at times...as well as their military historians. Montgomery is a case in point.
Imagine this in the modern media.
I have no difficulty believing that.
But history is lies agreed upon.
Battle of Slapton as it relates to WW2.
The U.S.S. Maddox as it relates to the Vietnam War.
The U.S.S. Liberty, as it relates to the 1967 Israeli preamptive attack on Egypt.
The U.S.S. Indianapolis as it relates to the Atomic Bomb dropped in WW2.
Watergate as it relates to the reason for the break-in.
Waco as it relates to the charges against the Branch Davians
The recorded history of each of the above events differs considerably from what is now known.
The dirty little secret of the Gulf War is that "friendly fire" accounted for 13,974 of the 58,226 names etched on the walls of black granite panels.
I've been told that is war.
For the same reason Churchill did not evacuate locations he knew were going to be hit with Vbombs. Didn't want the Hun to know we had broken their code.