The Longwy (Wreck)

 shipwreck, invisible

The 2315 ton French steamer Longwy was one of the victims of a German UC-class mine-laying submarine engaged in setting a widespread field of mines across the approaches to Glasgow and the Clyde.
The Longwy, bound for the Clyde from Bilbao with a cargo of iron ore, was 3 miles off Corsewall Point on the Scottish shore of the North Channel out of the Irish Sea when the torpedo hit her, on the morning of 4 November, 1917.
Though it was a torpedo which sank the ship, the course set by Captain Yves Legall might well have ended with a mine explosion anyway. At this late stage of the war, the German mine-laying subs were planting their cargoes close inshore, to catch Allied shipping hugging the coast in an effort to dodge U-boats operating in deeper waters.
The Longwy was built in 1903 in Nantes and, when launched, was 282ft long with a beam of 40ft and a draught of 19ft. She was powered by a three-cylinder triple-expansion steam engine, made by Schneider and Co of Creusot.