Hi Alex,
Duchess of Cornwall, on a voyage from London to Le Havre, was indeed sunk by a submarine, it was UC-26. The sub had to make 2 attacks: the first torpedo she fired missed the target, she regained position and fied a second, which sank the ship, 5 nm N of P.te de Barfleur with 23 dead among the crew.
Can't help you with photographs,
good luck, Brian