If you&#x27;re not that familiar with D-day, you may not realize how extensive the logistic preparations were. This was Eisenhower&#x27;s achievement - his background was in logistics.  Moving an army across the English Channel was hard enough.  Forcing an opposed landing was hard. But once landed, supplying a huge mechanized army for an attack across France presented problems never before solved.<p>Preparations for the landing involved the development of landing craft of various sizes, amphibious vehicles, (including the DD Sherman, which floated, sort of, using canvas screens), and specialized vehicles such as flail tanks, for beating a path through minefields. That&#x27;s all well known.<p>Less well known are the second phase logistic innovations. There were the Mulberry portable harbors, barges which were towed across the Channel and sunk to provide breakwaters, along with jack-up rigs for wharfs and pontoon bridges for access. These provided the first way to get trucks and tanks across in quantity. The temporary harbors were destroyed in a storm, but by then enough soldiers and gear were in France to capture a real harbor at Cherbourg.<p>Fuel was in drums in the early phases. But 17 fuel pipelines were unwound from huge spools (&quot;Conundrums&quot;) across the channel. That took care of fuel supply. Mostly; there were still
shortages in-theater.<p>There were lots of other new logistic systems, including, in the later stages of the invasion, prepackaged Coca-Cola bottling plants.  (64 transportable bottling plants were eventually deployed.) The British fabricated low-cost railroad locomotives to be transported to Europe for the invasion. The US Army had railroad units which could quickly repair track and bridges.  The famous Red Ball Express, an endless chain of trucks traveling at 25MPH, did much inland supply.  The Allies had plenty of trucks.  The Germans were still using <i>horses</i> for road transport in WWII. They planned to ship 4000 horses across the channel for the invasion.<p>This may seem like overkill, but the Dieppe raid disaster convinced the Allies that invasion without heavy logistics backup would be very risky and could lead to huge armies being stranded and lost.<p>Sealion doesn&#x27;t seem to have included comparable plans for supplying German troops in Britain. Nor was the German invasion of Russia supplied adequately.  (German plans did not include supplying the troops with winter gear. It was supposed to be a blitzkreig. Didn&#x27;t work out that way.)<p>The WWII experience led to one of the great strengths of the American military - the ability to supply a sizable army almost anywhere.  Few armies worldwide can do that at all.  It&#x27;s insanely expensive to do this, but it&#x27;s a lot better than losing.<p>For a modern view of military logistics, see &quot;Moving Mountains&quot;, by Gen. Patronis, who managed logistics for the Gulf War in the 1990s.  Even though the combat part of the war lasted only 4 days, they were prepared and supplied for a long, hard war. Lots of supplies were unused and were shipped back to storage.  This is a lot better than underestimating the enemy.