Operation Sea Lion, also written as Operation Sealion (German: Unternehmen Seelöwe), was Nazi Germany’s code name for the plan for an invasion of the United Kingdom during the Battle of Britain in the Second World War. Wikipedia

Operation Sea Lion
In preparing for the invasion of Great Britain (Operation Sea Lion), a vast amount of information, including maps and photographs, was assembled by the German military. This resulted in the production of a series of military/geographical assessments, showing what might be found by those arriving. This material was also used in a military evaluation of the regions of the British Isles, and considered each from the viewpoint of invasion.

The full assessment for England and Wales consists of three thick A5 sized folders containing books and maps, plus eleven A4 sized folders, each containing maps and a book of photographs. There are 144 six-inch town maps marked with strategic locations, and almost 1500 black and white photographs in a set of the eleven folders.