I've known about it for over thirty years now...and my knowledge came from published material that anyone could read.
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 other day, I was watching a film on the Battle of Bastogne, a mere crucial town on the road to Belgium's pivotal port during the last German push called the Battle of the Bulge.
The 82nd and 101st Airborne units were sent in on foot, as some days were required to get the 4th Armored under Patton the 175 miles they had to traverse in icy conditions.
The infantry, with little food, heavy weapons or ammo went in in high spirits to face the German Panzer advance. A Sgt recounts how one of his men didn't have a weapon, let alone ammo. He in its stead, found a good stick, a cudgel if you will and went along repeating as he swung it, "I'll have me a rifle tonight."
In that battle of a few days for one town, ten times our entire KIAs in Iraq were incurred and shrugged off as what it took.
Like they said at Ground Zero to Bush: "...Whatever it takes!"
In my mind, the media has no stomach to defend and represent freedom and just order. They are a cancer in the body of a fighting nation.