M4 Sherman Duplex Drive Tanks
One of the problems confronting the planners was how to get tanks ashore in order to provide direct fire support for the infantry in attacking German strong points. The solution was the M4 Sherman Duplex Drive Tank (DD Tank). Getting a 32 ton tank to swim was a huge feat. As long as enough water is displaced, though, anything can float. So, canvas skirts were placed around the sides of the DD Tanks, and were held up with inflatable support tubes.
The tanks would be loaded into the LCTs and prepared for the mission. Then, they would be warmed up, the skirts would be raised, and the LCT door dropped. There was only two feet of clearance between the top of the skirt and the surface- freeboard. This meant that in rough seas the tanks could be easily swamped and sunk. At Utah Beach, the tanks were brought in 3,000 yards offshore as opposed to the planned 5,000 yards. This made all the difference. While still showing up 20 minutes late, the tanks did make it to shore because they had less distance to cover and the ocean was not as choppy. At Omaha, the tanks were unloaded 5,000 yards out, which lead to the majority sinking. In contrast, only one tank was swamped going in to Utah.
The tanks would be loaded into the LCTs and prepared for the mission. Then, they would be warmed up, the skirts would be raised, and the LCT door dropped. There was only two feet of clearance between the top of the skirt and the surface- freeboard. This meant that in rough seas the tanks could be easily swamped and sunk. At Utah Beach, the tanks were brought in 3,000 yards offshore as opposed to the planned 5,000 yards. This made all the difference. While still showing up 20 minutes late, the tanks did make it to shore because they had less distance to cover and the ocean was not as choppy. At Omaha, the tanks were unloaded 5,000 yards out, which lead to the majority sinking. In contrast, only one tank was swamped going in to Utah.
This video, courtesy of the NARA research facility, shows footage of DD Tanks, including the tubes inflating to raise the canvas skirts, and a tank swimming.