Because the overwhelming strength of the Allied fleet has kept the German and Austrian battleships safely locked up behind shore batteries, mine-fields and nettings, the Allies’ submarines have had comparatively few targets to try their skill on. The activity of the British submarines in the North Sea at the outbreak of the war has already been referred to, and a year later they found another opportunity in the Baltic. There the German fleet had the same preponderance over the Russian as the English had over the German battleships in the North Sea, but the British dreadnoughts could not be sent through the long tortuous passage of the Skagerrack and Cattegat, thick-sown with German mines, without cutting the British fleet in half and giving the Germans a splendid chance to defeat either half and then slip back through the Kiel Canal and destroy the other. So England sent some of her submarines instead. One of these joined the Russian squadron defending the Gulf of Riga against a German fleet and decided the fight by disabling the great battle-cruiser _Moltke_. Another, the _E-13_, ran ashore on the Danish island of Saltholm on August 19, 1915, and was warned by the commander of a Danish torpedo-boat that she would be allowed twenty-four hours to get off. Before the time-limit had expired and while three Danish torpedo-boats were standing by, two German destroyers steamed up, torpedoed the _E-13_, and killed half her crew by gun-fire: an outrageous violation of Denmark’s neutrality.[24]