Those American tank crews manning the Sherman DD tank as attempting swim ashore 6 June 1944 equipped with and "escape apparatus".
Tankers finding their "swimming" tank foundering and in an almost instantaneous manner rapidly sinking to the bottom that crew in a very confined space without a whole lot of egress available at least equipped with a breathing device that might sustain them underwater for a short period.
"The Davis Submerged Escape Apparatus (also referred to as DSEA), was an early type of oxygen rebreather . . . While intended primarily as an emergency escape apparatus for submarine crews, it was soon also used for diving, being a handy shallow water diving apparatus with a thirty minute endurance, and as an industrial breathing set."
"A small version of the DSEA, the Amphibious Tank Escape Apparatus (ATEA) was produced for use by the crews of amphibious DD tanks such as those used during the Normandy landings"
I can well imagine those Sherman DD tanks foundering and settling to the bottom in extremely rapid fashion. Crews attempting egress EVEN equipped with an ATEA at great risk from drowning. Anyone have an idea of what percentage of those crews in that DD tank battalion at Normandy perishing from the sinking of their tanks?