You may be interested in this answer I wrote earlier today actually about some of the issues, thought processes, and issues the US Army faced gearing up for ground combat in the war against the European Axis. Especially with earlier cross channel plans like ROUNDUP and SLEDGEHAMMER that were eventually cancelled or differed and from which OVERLORD was eventually developed.
But on the flip side the premise of your question is still factually incorrect. The first time US ground forces fought on the European continent in numbers would be 9 July 1943, as part of the Allied landings in Sicily as part of Operation HUSKY. Followed by the landings in Italy proper in September 1943.