Operation Sea Lion is available on the issue nº 49 of the spanish miniatures magazine "Wargames, Soldados y Estrategia".
Its a small wargame that simulates a "what if?" invasion of Great Britain by the German forces in September 1940.
The board is sized as an A4 page (29,7x21 cm) with the counters on another page the same size.
The counters represent mostly Divisions, but a few Brigades and Battalions are also available.
Sea and Air units, as well as other counters (mines, damage, etc) are available as well.
The game is an easy to play and rather simple one, even for its size, with a very simple naval and air phases, and combat mechanics.
The board and counter pages are included in the magazine, and the rules can be downloaded on its site. (see link, below)