The details of this submarine do not match any British type. The only class that Wyllie could have seen with a sloping casing aft was the 'H' class of 1915-19, none of which had the narrow conning tower he has shown. However, there is a photograph in existence, on the Naval-history.net website, of the submarine E13 (1914) stranded on the Danish island of Saltholm in August 1915. After being attacked by two German destroyers she was abandoned by her crew and the stranded and badly damaged boat was interned by the Danish authorities. The photograph shows the vessel as listing to port and there are some other similarities with this drawing, so it is possible that Wyllie saw a photograph and used it to produce this impression. The E13 stranded in the early hours of 19 August 1915 after a compass failure. Ffteen of the crew were lost by gunfire or drowning until the Danish torpedo boat 'Soulven' intervened and the German ships departed: there were 23 survivors. The wreck of the E13 was sold to shipbreakers in Denmark in December 1921.