Amphibious assaults, particularly against prepared opponents, are perhaps the single most difficult military operation you can contemplate. D-Day, arguably the most well-known such assault, required years of meticulous planning, prior experience with what to do and what not to do (Dieppe), a sophisticated buildup of materiel on UK, complete air and naval superiority, successful sabotaging by the French resistance to hamper German repulsive efforts, and one of the most impressive counterintelligence campaigns in history (Germany was transferring troops to Calais even after the assault started, because they were duped into believing it was merely a feint). Even then, it only barely succeeded.<p>Germany had absolutely none of those things. Most people arguing alternative history scenarios tend to suggest some way by which the RAF and RN basically cease to exist, and--as this article points out--even then, the plan was so half-baked that it would still have failed. Basically, it would have failed because the German high command had no idea how to do an amphibious invasion, had no preparation for it, had no preparation for how to maintain an invading force after the initial beach was cleared. In addition, the German blitzkrieg tactics masked the fact that Germany had poor logistics capability, which amphibious assaults are the poster child of: you need to carefully orchestrate obscene concentrations of soldiers and materiel in confined space and time (tide) restrictions.