Historically, the US Army did not use the LVT series vehicles in amphibious assaults in any number. There were a few present at the Normandy landings in use by the USMC and US Navy but these were a mere handful; less than a dozen or so. Anyway, what if the US Army had adopted the LVT series and had sufficent to land their first waves on Omaha and Utah beaches along with their use with the Rangers at Point du Hoc? I suspect that had these vehicles been bringing in the troops along with more supporting them with 75mm and 37mm guns that Omaha would have collapsed much faster and with far fewer casualties than occured historically. In several of the draws on that beach the first wave was pinned by little more than sustained machinegun fire. An armored vehicle crossing the beach to unload would have pretty much made that useless as a defense on its own.