[4] Later that year O 13, with the Dutch vessels O 12, O 15, Hertog Hendrik, Van Ghent, Kortenaer and Z 5, sailed around the North Sea, stopping at Gothenburg and Oslo.

In 1937 O 13 did convoy duty in the Strait of Gibraltar during the Spanish Civil War,[5] along with Hertog Hendrik, Johan Maurits van Nassau, Nautilus, Java and O 15.

[9] Since there are no German records about O 13 having been sunk it is assumed that the submarine ran into a mine, a distinct possibility since O 13 was patrolling in an area known to have been mined,[10][11] possibly the same minefield where the Polish submarine ORP Orzeł was lost.

[12] Moreover, the newest analysis of the Wilk's damages shows the most probable possibility: that it collided with a German minefield protector buoy, rather than a submarine.

[16] In September 2012, the Royal Netherlands Navy announced they would renew the search with new, advanced equipment.