Erskine Childers 
The Riddle of the Sands [EPUB ebook] 
Illustrated

Considered the first proper spy novel, Riddle of the Sands is about two blokes floating about in a boat who suspect Germany is plotting an invasion from the Frisian Islands. The story may be fiction, but Childers knew both sailing and the Frisian Islands inside-out, and wrote non-fiction books and articles about how Britain needed to update its military strategy in the Baltic. It was Riddle of the Sands that made an impact, though.
Robert Erskine Childers (1870–1922), universally known as Erskine Childers, was the author of the influential novel The Riddle of the Sands and an Irish nationalist who smuggled guns to Ireland in his sailing yacht Asgard. He was executed by the authorities of the nascent Irish Free State during the Irish Civil War. He was the son of British Orientalist scholar Robert Caesar Childers; the cousin of Hugh Childers and Robert Barton; and the father of the fourth President of Ireland, Erskine Hamilton Childers.