The Sea-Girt Fortress: A Story of Heligoland, written by Percy F. Westerman and first published in 1914, is a juvenile adventure novel set during World War I. The story follows two young sailors, Sub-Lieutenant Jack Hamerton and his American friend Oswald Detroit, who embark on a yacht cruise to Kiel but accidentally enter a restricted naval zone near Heligoland. Their adventure takes a perilous turn when they are arrested by German authorities on suspicion of espionage, leading them into a world of international intrigue and naval operations.
