SEALION

SEALION was the operational name of the German Wehrmacht's plan to land an army in the United Kingdom during the Second World War. Due to difficulties in securing air superiority over the English Channel and the Straits of Dover, as well as over Kent and southeastern Britain, and the lack of landing craft and overall inadequacy of the German navy, Fuhrer and Reichschancellor Adolf Hitler called off the invasion in late 1940.

The invasion of Britain in the summer of 1940 posed one of the greatest and overused alternate history scenarios of modern times. Since it presents an obvious POD with some very large changes, it's usually one of the first AH ideas a noob entering the field would come up with. As a result, various threads on SEALION have been started on AH forums across the internet; this in addition to the many thousands of pages in books and on web sites devoted to the plans and the actual implementation of SEALION.