The Zebrina was an anachronistic design, a three-masted sailing barge operating in the late years of World War I alongside oil-burning warships and early submarines.
Advances in the development of ship rigging allowed the 189-ton Zebrina to operate with only five sailors. She ran a fairly simple course between England and France, so when the ship was found aground south of Cherbourg in good condition but completely lacking a crew, naval authorities were at a loss.
The easy explanation was a U-boat attack. Common German practice was to allow merchant crews to board lifeboats or the U-boat itself before sinking the target with cannon fire, and it was assumed that a Royal Navy patrol had discovered and sunk the sub before it had the chance to destroy the Zebrina.
This ignored several facts, chief among them that the captain’s log was still aboard and U-boat captains always claimed such documents as proof of their claim. At the height of the war, Allied commanders had little time to investigate the mystery, and the barge was subsequently broken up. Post-war research never definitively put a U-boat along the Zebrina’s course.