Just why all but a couple of amphibious tanks were lost on Omaha is a mystery, but I saw show a few weeks ago that tried to explain it. The tanks were Shermans, with a propeller in the back, and very flimsy Rube Goldberg system of canvas floats and screens.
So long as the sea was calm, and the float didn't leak too badly, the Shermans could crawl along, straight towards the beach, at a few knots. They had to go straight towards the beach because the canvas screens were designed to be strong enough to be hit by waves in the stern, and to push through the water in the bow, but they could not take wave action against their long, flimsy, sides.
On Omaha, a cross current pushed the Shermans sideways, along the beach. If they had just kept going, and hit the beach down from where they intended to, they might have been OK.
But the high canvas screens blocked the crew's view in every direction, except up. Up, they could see the steeple of a French Church on top of the bluffs, and it is thought that they steered for the steeple. As the cross current pushed the Shermans further down the beach, they had to turn at an angle to keep their bows pointed at the steeple. Since the crews couldn't see the water in any direction, they didn't know that they were turning sideways, and one by one, waves hit their sides, collapsed the canvas screens, and they sank.
WOW! A fascinating and crushingly sad story. Thank you so much for taking the time to tell it.