Against a working total of roughly 2,400 barges, only about 800 were powered, and most of those were considered too weak to handle Channel currents unaided. Tugs would tow the barges across before releasing the powered vessels for the final approach. Unpowered barges would anchor near shore and wait for the falling tide to let troops unload. That left about two-thirds of the transport force stationary for hours, giving artillery time to find the range. Even powered barges depended on favorable tidal movement and reaching the intended landing sites. The predicted loss is at least 90 percent of the moored barges, a counterfactual judgment rather than an observed loss rate.
Chapter · 29:02-31:53
Towing barges across and waiting for the tide
The unloading plan left unpowered barges stationary for hours, giving British artillery time to destroy them.