LONDON — They went by air and by sea across the Channel to the beaches of Normandy.

In history’s greatest amphibious invasion, almost 7,000 vessels and 11,500 airplanes supported the 156,000 Allied soldiers who crossed from Britain to five beaches in France 75 years ago on June 6, 1944 — D-Day.

Beyond the cinematic re-enactments of noise and chaos and bloodletting, it is hard for subsequent generations raised on Europe’s expectations of peace — or, at the most, on the menace of the Cold War — to imagine how a truly hot war might have been.

Only a handful of veterans, now in their 90s and beyond, survive to recall how it was to spill from steel-sided landing craft into chilly seas to advance neck-deep in water toward beaches enfiladed by German snipers and machine-guns, strewn with land mines and bodies and barbed wire. Or to spring into the night from low-flying aircraft to secure bridges inland.